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Optimizing the Stimulus to Maximize System Performance

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Presentation on theme: "Optimizing the Stimulus to Maximize System Performance"— Presentation transcript:

1 Optimizing the Stimulus to Maximize System Performance
Hello and welcome to Agilent’s measurement seminar. My name is Neveia Chappell, and I will be presenting the “Optimizing the Stimulus to Maximize System Performance” paper. Transceivers are becoming more digitally implemented. Driving this trend is the consumer’s need for higher performance, lower cost, and better power efficiency. This shift creates new and different test challenges that did not exist with analog radios. Diverse test issues are encountered for the various subsystems and interfaces of the modern transceiver. This paper explores optimizing the signal stimulus to test the entire radio, its amplifiers, and the frequency conversion and baseband systems. Main Point: Introduce yourself and the paper

2 Main Point: Go over the agenda
Overview System functionality test and troubleshooting Amplifier test Frequency conversion system test considerations Baseband system test considerations Summary This presentation begins with a brief overview of the digital radio architecture. Next, the radio system functionality test issues are considered. Then the discussion will move from the system level to inside the radio. Amplifier stimulus and response measurements are examined. The next topic investigates how the signal generator’s level accuracy, spectral purity, and bandwidth impacts the radio’s frequency conversion system. Afterwards, baseband system test considerations are explored. Finally, the presentation is concluded with a brief summary. [Don’t say this: this is only in the application note->This application note assumes that you are familiar with basic analog measurements and technology basics. For more information on source basics see [1].] Main Point: Go over the agenda

3 Overview Superheterodyne radio architecture x + x x x x x Baseband
TRANSMITTER Digital signal processor/FPGA I x DAC Filter IF Filter FIR 0 deg Encoder + x Symbol Encoder PA IF LO 90 deg Q FIR DAC x Filter RF LO Baseband Frequency conversion Amplification Digital signal processor/FPGA I RECEIVER x Many modern digital radios have a basic block diagram similar to the one shown on this slide. The upper block diagram represents the transmitter, and the lower block diagram represents the receiver. Each block diagram has been divided into three sections. The first section, the baseband system, is mostly digital. Some of the digital components that are found in this section include the following: digital signal processor (DSP) application specific integrated circuit (ASIC) field programmable gate array (FPGA) digital to analog converters (DAC) or analog to digital converters (ADC) The baseband section also contains low pass analog filters. The next part of the block diagram is the frequency conversion section. The radios illustrated in this slide are superheterodyne radios. A superheterodyne radio mixes a transmitted or received signal with a swept local oscillator (LO) to produce an intermediate frequency (IF). This makes filter implementation easier. Typical superheterodyne transmitters and receivers have two different frequency conversion stages: an IF stage and a RF or microwave (MW) stage. The IF section typically consists of an I/Q modulator or demodulator, and is followed by a bandpass filter. Next is the RF/MW frequency conversion section. The transmitter will upconvert the IF signal to a higher frequency, and the receiver will downconvert the input frequency to an IF. The frequency conversion section consists of a RF or microwave mixer which will translate the frequency to the desired frequency range, and is followed by a bandpass filter. The last section of the block diagram is amplification. The transmitter contains a power amplifier, where as the receiver contains a low noise amplifier. Each section of this block diagram has different design and test challenges. Preselecting filter ADC Filter IF FILTER FIR 0 deg Decoder Symbol Decoder x LNA IF LO 90 deg ADC Q FIR x Filter RF LO Baseband Frequency conversion Amplification Main Point: Explain that radio can be divided up into 3 sections: baseband, frequency conversion, and amplification

4 Direct digital conversion
Overview Receiver architecture progression RF IF Baseband Superheterodyne ADC DSP RF LO IF LO Analog Digital Direct digital conversion RF Baseband Zero IF ADC DSP Digital radios are implemented in many different ways, and that is what these high-level block diagrams illustrate. The amount of digitization for a modern radio can vary. As DACs and ADCs become more advanced and as computational power increases, this digitization stage is moving closer to the antenna, and less analog components are required. This slide shows the digital progression of a receiver. Notice that in the Zero IF diagram, the downconversion section is completely digital and the IF stage is implemented digitally. This design eliminates the need for the analog IQ modulator and filter. As converter technology advances, it may be possible to bypass the analog conversion stage completely, as illustrated in the direct digital conversion implementation. This paper focuses on the superheterodyne radio design since this configuration remains common today. DAC RF LO Baseband to RF Analog Digital ADC DSP Analog Digital Main Point: Explain the digital radio evolution, and this paper will focus on the superheterodyne radio

5 Overview Common stimuli test points x + x x x x x 2 1 3 4 1 2 8 9 7 5
TRANSMITTER I Digital signal processor/FPGA 2 1 x DAC Filter IF Filter FIR 0 deg 3 4 Encoder + x Symbol Encoder PA IF LO 90 deg 1 2 DAC x FIR Filter Q RF LO Digital signal processor/FPGA 8 I 9 RECEIVER x Again, reviewing the superheterodyne radio, notice how similar the transmitter block diagram looks compared to the receiver block diagram. Similar types of stimuli and measurements are used for testing the transmitter and the receiver systems. For example, the amplifier in each section is tested for distortion, the IQ modulator needs analog IQ signals as a stimulus, the IQ demodulator needs an analog IF as the stimulus, the analog filters need an appropriate test signal to determine flatness and bandwidth, and a digital stimulus is needed to test the baseband subsystems. The numbered circles on the diagram illustrate common test points where a stimulus would be applied when testing the radio. There are corresponding points to measure the response to the applied stimulus. Because this paper will focus on how the test stimulus affects the test results, the measurement test points are not shown on the diagram. Another paper in this series, called“Using Innovative Signal Analysis Techniques to Assure Optimum System Performance”, focuses on measurement techniques. Preselecting filter ADC FIR Filter IF FILTER 0 deg 7 Decoder Symbol Decoder x LNA IF LO 5 9 90 deg 6 ADC Q FIR x Filter 8 RF LO Denotes test points Main Point: Explain all the stimuli test points and that the Tx and Rx both need a stimulus

6 Frequency conversion section Amplification section
System Functionality Test & Troubleshooting Agenda Frequency conversion section Baseband section Amplification section Overview System functionality test & troubleshooting Amplifier test Frequency conversion system test considerations Baseband system test considerations Summary This presentation will begin with the discussion of system level tests. Main Point: Transition to system functionality and troubleshooting section

7 Main Point: Explain what is system functionality test is
System Functionality Test & Troubleshooting What is system functionality test ? Fading Transmitter Receiver transmission channel What is system functionality test? Communication quality between a transmitter and a receiver depends on a number of factors, including the general quality of the propagation channel. As the transmitted signal gets absorbed by the atmosphere and reflects off of objects, it experiences fluctuations in its amplitude and phase and this phenomenon is generally referred to as fading. System functionality tests indicate how robust the radio performs under these conditions. These tests help determine how robust the radio is in its’ operating environment. Additionally, this is a good indicator of how well it will combat fading, interferers, and other environmental conditions. It is important to perform this testing efficiently and economically. For wireless and satellite communications, reliable performance is commonly verified by measuring bit-error-rate (BER) or packet-error-rate (PER), or some variation of these two metrics under realistic field conditions. Another paper in this series discusses measuring BER and PER. This paper is called “Shortening System Design Cycles; Combining Simulation and Test”. For radar applications, reliable performance is commonly verified by traditional sensitivity and selectivity tests using common metrics such as signal-to-noise (SNR) ratios and signal to noise including distortion (SINAD) ratios. BER/PER analysis Interferers Main Point: Explain what is system functionality test is

8 Main Point: Explain why system functionality testing is important
System Functionality Test & Troubleshooting Why is system functionality testing important? WLAN PCMCIA card WLAN Tx Interference WLAN cards are inexpensive Rework increases price “Perfect” quality is expected Interference Satellites are expensive Rework may not be possible A/D applications must be reliable Why is system functionality testing important? System functionality testing and troubleshooting is an economic necessity across a range of wireless technologies. For example, WLAN devices are very cost sensitive. Consumers expect these devices to perform well. If these cards are defective or fail, the already low price of these cards make post-sales support too expensive for the manufacturer. At the other end of the price spectrum, satellite devices are really expensive. This device must work reliably because it will be launched into space, and repair or adjustment may not be possible, and if it were it would be very expensive and limited. Aerospace and defense devices are costly and must be reliable. System failure of these devices can have a huge financial and security impact Main Point: Explain why system functionality testing is important

9 Record the test signal & play it back
System Functionality Test & Troubleshooting How to perform system functionality tests Field test Commercial fader DUT (Rx) DUT (Rx) Record the test signal & play it back How to perform system functionality test? There are basically two different ways system functionality test can be performed. One way to perform system functionality test is to try it in the environment in which it will be used. This type of test is referred to as a “field trial”. A more efficient and economical approach is to use a simulated test signal. Fading can be simulated with a commercial fader. There are a number of commercially available faders, with a wide range of features and prices. Depending upon their capability, faders offer a realistic simulation of actual conditions, usually at lower cost than a field trial. In addition, using a controlled stimulus enables the radio to be tested over a full range of repeatable conditions that may not be encountered during a field trial. If a radar or a satellite system is being tested, a commercial fader may not provide a realistic simulation of its actual operating environment, so another test alternative is to make an actual recording of the real signal, and use this recording as the test stimulus. This is frequently referred to as waveform capture and streaming. This application usually requires two separate pieces of test equipment; a vector signal analyzer to make a recording and a vector signal generator and a PC to play back it back. The vector signal analyzer makes a recording of the actual stimulus from a field trial. The recorded waveform is then saved to a PC for further analysis. Once the suspected cause of the radio problem is identified, streaming software and hardware is used for waveform streaming to play the problem segment repetitively until a solution to the problem is found. The waveform can be continuously streamed off the PC’s hard drive, upconverted to RF or MW, and applied to the receiver. This test is repeatable; you can play the signal as many times as needed, and the “field trial” only has to be done once. When deciding on which test approach to take, remember that the features and specifications of the test equipment influences the measurement results. DUT (Rx) Record Play back Main Point: Explain that there are three ways to perform system functionality tests: field test, commercial fader, and record the test signal and play it back

10 Main Point: Pros & cons of field tests
System Functionality Test & Troubleshooting Field trial considerations Advantages Real operational conditions Disadvantages Expensive Inefficient Non-repeatable Limited: cannot cycle through full range of conditions Rework may not be possible The advantages and disadvantages of each approach will be discussed now. Field trials are a great way to prove that the design works under normally expected conditions.However, there are many disadvantages associated with field trials. This test method can be quite costly and time consuming if the stimulus happens to be a jet airplane. Also, field trials may not be repeatable and are not an efficient way to troubleshoot design problems. Additionally, the full range of operating conditions are not likely to be cycled through. Moreover, if a device such as a launched satellite is not operational, rework is not likely or even possible. To guarantee that the design will not fail the field trial, pretesting should be performed. This will ensure that the design will function in normally expected and worst case operating conditions. Main Point: Pros & cons of field tests

11 System Functionality Test & Troubleshooting
Fading considerations Interference Multiple RF/MW channels Multiple RF/MW channels Fading Profiles & Multiple Paths If a fader is used, there are five key fading features that need to be considered. The first key feature is the various “fading profiles” available on the fader. Fading profiles are statistical fading channel models. They are also commonly referred to as the fading distribution models. The ability to simulate different fading profiles is essential for evaluating receiver performance in a variety of physical environments. The fader should support both small scale and large scale fading models or combinations of the two. The large scale fading is used to describe the signal level at the receiver after traveling over a large area (hundreds of wavelengths). Small scale fading is used to describe the signal level at the receiver after encountering obstacles near  (several wavelengths to fractions of wavelengths) the receiver. Testing for both large and small scale fading enables the simulation of rapid signal fluctuations, due to small movements of the receiver, and slow changes in average power, caused by shadowing effects of distant objects. Common fading profiles include: Rayleigh, Rician, log normal, Suzuki, and pure Doppler . The second important features faders offer is multipath. In a typical wireless environment, a signal will travel along multiple paths from the transmitter to the receiver. Each path can have a different amount of attenuation, delay, and fading type. Simulating different numbers of paths is important because indoor propagation typically generates more paths than outdoor propagation. Here again, it is important to be able to simulate both kinds of environments. The third feature is the number of channels available on the fader. The number of channels indicates how many RF or channels that can be simulated. This is important for antenna diversity testing. At least two channels are needed to test transmitter or receiver diversity. The fourth consideration is the available bandwidth on the fader. The bandwidth is important because a sufficient amount of bandwidth is needed to include the desired test signal. With today’s wideband signals, such as the 22 MHz wide WLAN signal, bandwidth is probably the most serious limitation of commercial faders. The fifth item that needs to be considered is the amount of fading provided with your fader. A realistic faded signal will likely undergo some amount of reflection, diffraction, and scattering. Additionally because the receiver is moving relative to the transmitter, some amount of Doppler shift will occur. In real fading conditions, these properties are continually changing relative to one another. Some commercial software products may only implement a simplistic fading model that simulates constant phase reflection. This one component of fading, which is referred to as either multipoint reflection or simply multipath, does not account for any dynamic refraction or scattering of the transmitted signal. Nor can Doppler shift be simulated with multipath alone. Multipoint reflection only simulates how the signal changes with a constant phase and no Doppler shift. This amount of fade can give the designer a rough estimate of how his receiver will perform under stationary operating conditions. However, if a more accurate simulation is needed, it is recommended to use a commercial fader. Required bandwidth increases as the number of paths increase Main Point: Key fading features: fading profiles, multipath, number of channels, bandwidth, and various levels of fading implementation

12 System Functionality Test & Troubleshooting
Waveform recording & streaming considerations Memory depth Impacts recording time (signal analyzer) Impacts play back time (PC and signal generator) Converter Resolution Impacts quantization noise, fidelity, and dynamic range Signal analyzer’s ADCs Signal generator’s DACs Bandwidth Wide enough for capture & playback Amplitude Sample time If the waveform capture and streaming setup is used, the choice of test equipment still influences the measurement results. Some items to consider when choosing what test equipment to use for this application are memory depth, converter resolution, and the test equipment’s available bandwidth. The vector signal generator and the vector signal analyzer each have their own different capabilities. Memory depth determines the maximum amount of record time on the vector signal analyzer and the maximum amount of time that a waveform can be played back on the vector signal generator. Enough memory is required to adequately capture a long enough time record to represent the actual range of signal conditions. Also BER tests need enough data to be statistically significant. Converter resolution is another important consideration. The converter's bit resolution determines the fidelity of the signal and the amount of dynamic range available. Bit numbers are used to describe the analog resolution of an ADC in the VSA, and the DAC in the vector signal generator. This resolution is the smallest amount of analog change that can be detected by the converter. The greater the number of bits available for each sample point, the more accurately it will be represented. The last consideration is bandwidth. The bandwidth each piece of test equipment needs to be wide enough to accurately record and play back the signal. It may be difficult to find a solution that has both enough bandwidth and memory depth to meet your need. Amplitude Frequency Main Point: 3 considerations to choosing a commerical fader: memory depth, convertor resolution, and bandwidth

13 Amplification section Amplification section
Amplifier Test Agenda Baseband section Frequency conversion section Amplification section Overview System functionality test and troubleshooting Amplifier test Frequency conversion system considerations Baseband system considerations Summary The next part of the discussion will focus on the inside of the radio. It will begin with testing the radio’s individual subsections. The amplifier section will be discussed first. Frequency conversion section Baseband section Amplification section Main Point: Transition slide to amplifier test

14 Why is amplifier characterization important?
Amplifier Test Why is amplifier characterization important? In-channel distortion Power Out Power In Amplitude Amplitude Amplifier Frequency Frequency Why is amplifier characterization important? Transmitter power amplifiers (PAs) play an important role in boosting signals and directly affect maximum range and antenna size. However, the non-linear response in PAs can produce intermodulation distortion (IMD) products that lead to in-channel and out-of-channel interference and degradation of the bit error rate. There are many methods that can be used to characterize nonlinear behavior. Out-of-channel distortion Main Point: Explain why amplifier characterization is important

15 Amplifier Test How to characterize nonlinear distortion Stimulus
Stimulus Response Traditional stimulus/response test Two-tones, multitone, noise TOI, IMD, NPR Complex stimulus/response test Digitally modulated single and multicarriers ACPR, SEM, EVM Evaluating a device's distortion due to its non-linear transfer characteristics is useful in determining the limits of an amplifier's response and the optimum operating range of a device. There are many different ways to characterize the amplifier’s nonlinear distortion. Many of you are probably familiar with the traditional stimulus/response tests, and these tests will be will be discussed first. These types of tests are used when actual test signal is not available or known. This section will be divided into testing narrow band components and broadband components. Common response metrics of these tests are third order intercept (TOI), IMD, and noise power ratio (NPR). The complex stimulus/response test discussion will follow. A complex stimulus should be used if the digitally modulated signal is available, and why this is important will be discussed. Common response metrics of these tests are adjacent channel power ratio (ACPR), spectral emission mask (SEM), and error vector magnitude (EVM). Main Point: Briefly explain the various ways nonlinear distortion is characterized

16 Amplifier Test Test narrow band components Two-tone TOI & IMD In-band
2f1- f2 2f2-f1 Amplitude DUT . . . f1 f2 f1 f2 Frequency A two-tone test is used to test narrow band components, for in-band distortion. Two-tone test signals are used to characterize the 3rd order IMD. This nonlinear behavior is important to quantify, as it can cause severe signal distortion. IMD is measured by examining the output of the device under test (DUT) with a spectrum analyzer while the DUT is being stimulated with two tones. Based on the measurements of the 3rd order IMD, the TOI can be determined. TOI a figure of merit that is used because it is mostly independent of the input power, meaning that as the two tones increase or decrease in power, the intercept point remains fairly constant 3rd order IMD Main Point: Explain how a two tone test is used to test narrow band components to measure TOI

17 Test broad band components
Amplifier Test Test broad band components Multitone test Noise power ratio test Broadband components cannot be tested with a two-tone stimulus. If the actual stimulus is not available to test the broadband device, then either a multitone or a noise power ratio test should be performed. These stimuli have a more realistic power characteristic than that of two tones. These power characteristics are needed to adequately test broadband components. The multitone and NPR stimuli stresses the amplifier with the required peak-to-average power ratio. The multitone test measures out-of-band distortion, whereas a noise power ratio test measures in-band distortion. Each of these tests will be discussed separately. Amplitude Amplitude Out-of-band tests Frequency In-band tests Frequency Main Point: Explain there are two types of stimulus to test broadband components: multitione for out of band tests, and NPR for in band tests.

18 Before: Non-compressed signal After: Compressed signal from distortion
Amplifier Test Complementary cumulative distribution curves AWGN (reference) Before: Non-compressed signal Probability Before each stimulus is discussed, the complementary cumulative distribution function (CCDF) curves will be briefly reviewed. The CCDF curve provides statistical insight into the percentage of time the DUT will be subjected to power deviations from the average with respect to the level of deviation This is useful if the peak power information is needed prior to applying the signal to the DUT, and also provides design insight into headroom tradeoff for devices like power amplifiers. CCDF curves have become standard tools for many companies that design, evaluate and use power amplifiers. They are a clear and easy indication of operation relative to distortion. This CCDF curve shows a signal both with compression and without. This is a convenient tool for designers because the radio does not need to be complete to evaluate if the component is in distortion. The actual test signal does not have to be used, but the power characteristic of the stimulus that is used should sufficiently represent the actual test signal. Typically the power amplifier designer compares the CCDF curve of a signal at the input and output of an RF amplifier. If the design is correct, the curves will coincide. However, if the amplifier compresses the signal, the peak-to-average ratio of the signal is lower at the output of the amplifier, which means the CCDF curve decreases. The amplifier designer would need to increase the range of the amplifier to account for the power peaks, or the system designer could lower the average power of the signal to meet the power limitations of the amplifier. Similarly, CCDF curves can also be used to troubleshoot a system or subsystem design. Making CCDF measurements at several points in the system allows system engineers to verify performance of individual subsystems and components. {For the application note only; don’t say this: For a more detailed explanation on CCDF curves see [3].} After: Compressed signal from distortion Peak/Average dB Main Point: Explain what the CCDF is and what it is used for

19 Amplifier Test Multitone: phase relationship impacts CCDF
Equal phase set: crest factor = dB When a multitone test signal is used to test the broadband component, the relative phase relationship between the tones impacts the CCDF characteristics of the signal. In the time domain, the composite waveform is the summation of each sinusoid (i.e. tone). Changing the phase the sinusoids with respect to one another will affect whether they sum constructively, increasing the crest factor, or destructively, decreasing the crest factor. Because a devices IMD performance varies depending upon the signal level that is applied to it, averaging measurement results from phase sets is recommended. The worst case scenario is using a constant phase set. The crest factor and peak-to-average characteristics of a multitone signal can quickly be determined by plotting the CCDF. Notice in the upper CCDF plot, tones that have equal phase relative to one another have a crest factor of dB. This is the worst case scenario, and is not a realistic operating condition. When the multitone signal was created with a random phase set, then the crest factor was reduced to 6.70 dB. Random phase set: crest-factor = 6.70 dB Main Point: Explain how the phase relationships between relative tones impact the CCDF

20 Multitone test setup: CW sources
Amplifier Test Multitone test setup: CW sources 1 CW source needed for each tone Spectrum analyzer CW source Isolator AMP LPF + CW source Combiner DUT Traditional two-tone and multitone signal generation methods that are used to perform IMD measurements are equipment intensive, particularly as the number of tones increases. Tones from multiple CW signal generators are summed together to create the desired test stimulus. + CW source + Denotes isolators Main Point: Explain the test setup for multitone using CW sources

21 Multitone test considerations: CW sources
Amplifier Test Multitone test considerations: CW sources Advantages Established test procedure Common test equipment Disadvantages The advantage of using CW sources as a multitione stimulus is that this has become a well established test procedure and can be accomplished with common test equipment found in a lab. However, there are many drawbacks to this approach. One disadvantage is that this is a relatively complicated test setup with a high overall cost of test, although this approach has been used for many years due to a lack of reasonable alternatives. To minimize measurement uncertainty, it is also important to ensure there is adequate isolation between the individual signal generators so that they do not intermodulate with each other prior to the input of the DUT. Additionally, signal parameters are not easily modified. Adding another tone requires significant amount of work, so tests can be time consuming. Accurate test results require the ability to systematically change the initial phase of each tone so that repeatable tests are possible. The main shortcoming associated with this test setup is the inability to initialize the phase of the CW signal generators. Monitoring the variability in IMD performance on a spectrum analyzer over a period of 5 to 10 minutes reveals that the phase relationships of the signal generators change over time. As previously discussed, this is desirable for gathering IMD results from CW sources with different relative phase relationships. However, the signal generators drift relatively slowly with respect to one another and cannot be systematically initialized. Consequently, this test approach requires too much time to obtain test results statistically representative of real world operating conditions. Finally, summing multiple CW signal generators can be very expensive. It is equipment and capital intensive. Complicated test setup Time-consuming to change signal parameters Difficult to generate repeatable random tones Expensive Main Point: Explain the Pros and cons of using CW sources for multitione tests

22 Multitone test setup: vector signal generator
Amplifier Test Multitone test setup: vector signal generator 1 vector signal generator creates many tones Reduce cost Simplify test procedure Save time Repeatable test setup Accurate test results Control signal parameters Utilize digital predistortion (DPD) capabilities of the multitione signal creation software Vector signal generator DUT Isolator Instead of using many different CW sources to create the test signal, just 1 vector signal generator can be used to create thousands of tones. There are many advantages to using a vector signal generator as a test stimulus. One advantage is that the cost of test is reduced. A multitone test signal traditionally required summing multiple CW signal generators. Now this can be accomplished with one vector signal generator. The second advantage is that it simplifies the test test procedure. Now, setting a few basic waveform parameters on the vector signal generator is all that is required to create custom two-tone and multitone IMD test signals. Additionally, time is saved. Less time is spent setting up the desired test stimulus and more time is spent making measurements. To optimize testing with multiple phase sets, use the waveform sequencing capability of the baseband generator to minimize the test waveform switching time. The fourth advantage is that this is a repeatable test setup. The first step to achieving repeatable test results is finding a repeatable test stimulus. With vector techniques, test waveforms can be easily stored and quickly recalled for playback ensuring that the DUT is subjected to an equivalent test signal every time. The fifth advantage is that this test setup gives accurate test results. A series of multitone signals with random phase sets are required to adequately simulate real world operating conditions. Random phase sets can easily generated directly from signal generator’s front panel or remotely using the GPIB or the LAN interface. The sixth advantage is that the signal parameters can be easily controlled. Tones can be enabled and disabled at will. Common signal parameters, like relative tone spacing and power, can be easily modified. Also, phase distributions can be set with digital accuracy. Finally, digital predistortion can be used to optimize the test signal. Spectrum analyzer Main Point: Explain the advantages of using a vector signal generator as the stimulus for multitione tests

23 Amplifier Test Multitone: example Minimize test stimulus IMD …
Signal Studio for enhanced multitone software Minimize test stimulus IMD … even at the output of an external power amplifier! Low IMD reduces test uncertainty To test the amplifier for distortion, a clean test signal is needed. Agilent’s Signal Studio for enhanced multitone software uses digital predistortion to create a clean signal. This slide shows an example of how Agilent uses digital predistortion to enhance the test signal. This software can improve the IMD performance not only from the signal generator, but also from devices, such as power amplifiers, inserted between the signal generator and the DUT. The ability to add devices and then correct the signal at the output of the devices, plus the signal generator, is an excellent benefit, saving time and providing a cleaner test signal to reduce measurement uncertainty! Vector signal generator DUT IMD products from DUT Spectrum analyzer Non-linear distortion measurement Main Point: Explain this example of using Signal Studio for enhanced multitone uses predistortion to clean up the test signal, and any components inserted into the system

24 Main Point: Explain how the IMD was improved by 25 dB
Amplifier Test Before & after digital predistortion 25 dB improvement Before… This slide shows how much the multitone test signal been improved with the digital predistortion applied with Signal Studio for enhanced multitone. Notice that the test signal has been improved by 25 dB. …and After Main Point: Explain how the IMD was improved by 25 dB

25 Amplifier Test Images v I/Q skew of baseband waveform I Q
Time, ns time skew, Q leads I Images resulting from I/Q skew In addition to IMD products, images can occur in systems that use I/Q modulators. If the tones are created in a non-symmetrical pattern with respect to carrier frequency, images can be visible. Images occur when there is a time skew between the baseband I and Q signals to be supplied to the I/Q modulator. However, images can be minimized with slight adjustments to the IQ modulator. Most vector signal generators give the user the ability to minimize the I/Q skew manually, or the signal generator can perform this adjustment automatically. Minimize images by adjusting the I/Q skew Main Point: Explain images are possible if the I signal is skewed with respect to the Q signal. This can be minimized with I/Q skew adjustments

26 Multitone test considerations: vector signal generator
Amplifier Test Multitone test considerations: vector signal generator Advantages Simple test setup and procedure Easy to modify signal parameters Improved signal quality Repeatable and accurate test results Save time and test equipment cost Disadvantages Up to now, only the advantages of the using the vector signal generator for multitone tests have been discussed. However, there are some disadvantages as well. One is is available output Power. It is important to note that when using a single signal generator, the total power available from the signal generator is divided into each enabled tone based on the relative tone power settings. As a result, there is less power available per tone as compared to the traditional analog approach. Also, as the number of tones is increased, the peak-to-average ratio of the signal may increase. This must be taken into account in both the signal generator and with any booster amplifiers used to increase the composite signal power. The signal generator output power level should be backed off to account for the peak power of the multitone signal. This will ensure that additional distortion is not introduced by overdriving the signal generator’s power amplifier. When using external booster amplifiers, the same concern applies. In addition, a linear amplifier with a flat passband that is wide enough to accommodate the multitone signal should be used to avoid introducing additional distortion to the signal prior to the input of the DUT. Another issue is carrier feed through. Because an I/Q modulator is used to create the desired multitone signal, carrier feed through may be visible when an even number of tones are enabled, or with an odd number of tones and no tone placed at the center frequency. A high level of carrier feed through is undesirable since it will result in intermodulation products at one-half the tone spacing interval rather than at intervals equal to the tone spacing. Although carrier feed through cannot be eliminated, it can be minimized through a simple procedure. The IQ modulator consists of balanced mixers that combine the I, or in phase, and Q, or quadrature phase, signals. The I and Q signals use different identical paths and mixers in the signal generator but these paths are not perfectly symmetrical. Carrier feed through is created when this mismatch causes a DC offset that mixes with the carrier frequency and appears at the RF output of the signal generator causing the carrier to appear at the output. The carrier feed through is unstable over temperature and time. This feed through can be minimized by performing an I/Q calibration and adjusting the I/Q modulator’s offsets. The third issue is setting random tone spacing. Some multitione software does not allow directly setting arbitrary tones. However, this is overcome by turning on more tones than desired, and disabling select tones. This method enables random tone spacing to be set. Output power distributed Carrier feedthrough Main Point: Pros and cons of using a vector signal generator for multitone test

27 Main Point: Explains what NPR is
Amplifier Test What is noise power ratio (NPR)? Noise Stimulus DUT Amplitude Amplitude Earlier in the presentation, there was mention to a second type of amplifier test that is called noise power ratio. For wideband components, two-tone tests do not adequately characterize the non-linear behavior in the amplifier's pass band. Test results tend to vary considerably depending on where tones are placed in the passband of the DUT. As a result, NPR is commonly used for this purpose instead. NPR measurements are used to characterize in-channel distortion of wideband amplifiers. Since the amplifier’s large output masks the in-band distortion, a notch, or band stop, filter is required to remove a slice of input signal spectrum corresponding to the passband. NPR is the ratio of the power of the spectral components in the passband of a single channel to the power of those in the notch of a single channel at the output of the device. Both measurements should have the same bandwidth. Frequency Notch Frequency Noise generated By DUT Main Point: Explains what NPR is

28 NPR test setup: CW and noise source
Amplifier Test NPR test setup: CW and noise source NPR stimulus requirements Band Stop Filter Up converter DUT Noise Source IF RF LO What does an NPR test setup look like? Traditionally, a CW source and a noise source are used to generate a stimulus for NPR measurements. Next, the noise signal is up-converted to the desired frequency using a CW source and an external mixer. Then, a band-stop filter corresponding to the amplifier passband is used to create a notch in the signal. Finally, NPR is measured by comparing the relative power of the spectral components in the notch with and without the amplifier in the circuit. This test setup requires a lot of components, can be time consuming to setup, and the test results are not very repeatable. Additionally, to test different frequencies requires using different filters. CW source Spectrum analyzer Main Point: Explain the test setup using using a CW and noise source for NPR measurements

29 NPR test setup: vector signal generator
Amplifier Test NPR test setup: vector signal generator NPR stimulus requirements DUT LAN or GPIB Vector signal generator Signal Studio for NPR software Save time with simplified test setup Accurate test results Movable notch without analog filters Better dynamic range Repeatable results Phase and CCDF Another way to perform an NPR test is to use a vector signal generator as the test stimulus. This is an easier method to create the stimulus required for this test. NPR signal creation software can be used create this test signal, which is then downloaded to the vector signal generator to be played back at RF or MW. The advantages of this setup is that it saves you time because the setup is simpler, has a moveable notch without using analog filters, and generally has better dynamic range than the traditional approach. Additionally, it is repeatable in terms of exact phase and CCDF characteristics. Spectrum analyzer Main Point: Explain the advantages of using a vector signal generator for NPR tests

30 Advantages of pseudo-random tones over analog noise
Amplifier Test Advantages of pseudo-random tones over analog noise Pseudo-random tones Analog noise Better dynamic range Amplitude Amplitude Frequency Frequency Agilent’s Signal Studio for NPR software does not actually create a true noise signal, but thousands of pseudo-random phase tones. It has similar power characteristics as analog noise. Additionally, with the pseudo-random tones, better dynamic range is achieved because it is possible to use digital predistortion to improve the quality of the original signal. Moreover, the notch is created digitally, which results in a steeper filter. One other advantage the NPR software offers, is that it has a flatter amplitude, which is made possible with digital predistortion. Better signal-to-noise ratio Steeper filter Flatter amplitude Main Point: Explain that Signal Studio for NPR is not really a true noise signal but pseudo-random phase tones. However, there is better dynamic range, ect…

31 Digitally modulated single and multicarrier
Amplifier Test Complex stimulus/response Digitally modulated single and multicarrier ACPR, SEM, EVM Power In Power Out Amplitude Amplitude Amplifier Up to now, two types of generalized methods of testing amplifiers has been discussed. Of course, ultimately it is desired to test with the actual complex digitally modulated signal. Many wireless communication standards have specific types of tests that the device must pass. Some of the more common tests are ACPR, SEM and EVM. The purpose of ACPR and SEM measurements, is to ensure that the device does not create interference to other devices. For a & g WLAN amplifiers, EVM has been used as a figure-of-merit to characterize non-linear distortion. This is because some of the WLAN signals use a 64-QAM modulated signal, and in-band distortion is especially critical. WLAN signals are tested for out-of-band distortion using SEM. If the complex stimulus can be created using commercially available software packages, generating this stimulus is straightforward. However, to get valid measurements for ACPR, SEM, and EVM the test signal must be properly constructed. The CCDF curve shows whether or not the signal has been correctly generated. These considerations will be discussed now. Frequency Frequency Main Point: Introduce the concept of complex/stimulus response. Should use this test signal if available because it is most realistic

32 Amplifier Test Timing and phase offsets impacts the crest factor
AWGN signal (used as a reference) Multicarrier W-CDMA with no offsets applied 18 dB crest factor! In code-division multiple access (CDMA) systems, the power statistics of the signal vary according to how the signal is configured. Notice the 18 dB crest factor in this CCDF plot. This is because the signal was not correctly configured. If the CDMA code channels are not offset in time relative to each other, the CCDF will be higher than expected. To minimize the CCDF curve, it is recommended to randomize the timing relationship between the code channels, as well as randomizing the code channel numbers. Both of these are simple adjustments in the signal generator. It is also recommended to randomize the phase relationships between multicarrier signals to minimize the crest factor. If the phase relationships are not randomized, the CCDF curve will increase. This also applies to systems that use constant amplitude modulation schemes, such as GSM. Multicarrier signals are commonly used for base station transmitters used for cellular communications. If the timing and phase offsets are ignored, then the peak to average power can be higher than expected, and may not be accounted for in the design. Signals with different peak-to-average statistics can stress the components in the radio in different ways, causing different levels of distortion. High peak-to-average ratios can cause cumulative damage in some components. Apply timing & phase offsets for CDMA Randomize code channels for CDMA Apply phase offsets for multicarrier Main Point: Timing and phase offsets of the waveform impacts the crest factor. To minimize the crest factor randomize the timing & phase offsets, randomize code channels, and apply phase offsets for multicarrier signals

33 Signal before clipping
Amplifier Test Use clipping to limit the signal peaks Signal after clipping Signal before clipping Gaussian noise Another way to decrease the power peaks of the waveform is to artificially limit the peaks by waveform clipping. High power peaks can cause intermodulation distortion, which generates spectral regrowth. This is a condition that causes interference with signals in adjacent frequency bands. This slide shows the impact of clipping the waveform, and not clipping it. Notice that after clipping, the CCDF curve has been been reduced. Main Point: Use clipping to reduce the signal peaks on the waveform. This is an example

34 Common techniques to clip waveforms
Amplifier Test Common techniques to clip waveforms Circular Clipping Rectangular Clipping Peak power without clipping Peak power without clipping (clipping set to 100%) Vector representation of clipped I & Q I waveform Signal generators offer two common ways to clip the power peaks. Clipping may be applied to the composite I/Q signal, which is referred to as circular clipping. Alternatively, clipping may be applied individually to the I and Q signals. This is referred to as rectangular clipping. This slide illustrates the differences between rectangular clipping and circular clipping. Signal generators offer the option of clipping the peak power of signals before or after baseband FIR filtering. Clipping the signal before filtering smoothes any discontinuities in the resulting signal that can generate distortion. Optionally, the signal can be clipped after FIR filtering to simulate base stations that operate in this mode. It is suggested to perform the baseband clipping prior to the transmit filter to prevent sending square waves into the amplifier causing spurs. Baseband waveform Vector representation of clipped peak Clipping applied Clipping set to 80% Q waveform Main Point: Two common techniques to clip waveforms: circular clipping & rectangular clipping

35 Frequency conversion section Frequency conversion section
Frequency Conversion System Agenda Baseband section Frequency conversion section Amplification section Overview System functionality test and troubleshooting Amplifier test Frequency conversion system considerations Baseband system test considerations Summary The discussion of the amplifier section is now complete. Now the frequency conversion system will be examined. This system includes both the RF and IF frequency conversion sections. Frequency conversion section Amplification section Baseband section Main Point: transition slide to the frequency conversion system consideration

36 Frequency Conversion System
Frequency conversion system impacts measurements Vector signal generator Amplification section Baseband section Level accuracy Spectral Purity Bandwidth Many of the same test equipment characteristics that influence the amplifier’s test results also have a significant impact on the frequency conversion system. When testing the digital device, more than the basic analog specifications of the signal generator should be considered. The signal generator’s analog characteristics are different for wideband digital modulation, and these differences will be explored. Whether testing the entire receiver system with a signal generator, or using the signal generator to test subsystems within the radio, the signal generator’s specifications will impact the measurement results. Level accuracy, spectral purity, and bandwidth have the greatest impact on the test results. Amplification section Baseband section Vector signal generator Main Point: The signal generator’s frequency conversion system impacts measurement results: key considerations are level accuracy, spectral purity, and bandwidth of the signal genarator

37 Absolute Amplitude (dBm) Relative level accuracy (dB)
Frequency Conversion System What is level accuracy? 1 Absolute Amplitude (dBm) 2 Repeatability (dB) -10 dBm -10 dBm A B Amplitude Amplitude f1 f1 f2 Frequency Frequency 3 Relative level accuracy (dB) 4 Linearity (dB) What is level accuracy? Basically, level accuracy indicates how accurately the signal generator’s output power can be set. This is the absolute level accuracy, as shown on figure 1. Today’s high performance signal generators have absolute level accuracy of around 0.5 dB for certain operating conditions. Level accuracy varies according to the frequency range and power level. The signal generator’s level accuracy is maintained by monitoring the output power and adjusting the power as needed. This is usually done with an automatic level control (ALC) loop. Maintaining level accuracy for many different types of test signals is very complicated. In many types of tests, a number of level-related characteristics are more important than absolute level accuracy. These other characteristics will be discussed. The first of these is repeatability. Repeatability measures the ability of the signal generator to return to a given power setting after the frequency and/or power setting is changed. See figure 2. This figure shows starting at point A –10 dBm and at a frequency of f1, then the power and frequency are changed to –100 dBm and f2 respectively. Repeatability indicates how accurately the signal returns to point A again. This number is often 5 to 10 times better than the absolute level accuracy. Repeatability is important if you need to switch to a different frequency, and you need better level accuracy. The known systematic power errors can be calibrated out with a power meter. The second of these characteristics is relative level accuracy. This measures the accuracy of a step change from any power level to any other power level. This example is illustrated in figure 3. Like repeatability, it can be 5 to 10 times better than absolute level accuracy. Level accuracy is important when you need to switch power levels, and you need better level accuracy. The systematic error at the set power level can be calibrated out with a power meter. Relative level accuracy is particularly important to basestation power amplifier designers. These designers frequently add various components to their system, which results in power losses. For example, the PA designer has set his output power on the signal generator to 0 dBm. Since his system is so lossey, he is not as concerned about absolute level accuracy as relative level accuracy. When he changes his power level, he wants the same relative level accuracy. The last characteristic is linearity. This measures the accuracy of small power changes while the attenuator is held in a steady state (to avoid power glitches). It is similar to relative level accuracy, but this parameter is specified for modulated signals, because the type modulation and bandwidth of the signal strongly influences the linearity. -10 dBm 1 dB Amplitude Amplitude Amplitude 24 dB -100 dBm Frequency f1 f1 Frequency Frequency Attenuator hold on Main Point: Explain absolute level accuracy. Additionally, relative accuracy, repeatability or linearity may be more important than absolute level accuracy.

38 Frequency Conversion System
Why is level accuracy important? -110dBm spec. -110dBm spec. -110.5dBm actual -111dBm setting Power Output Power Output -114dBm actual -115dBm setting Frequency Frequency Why is level accuracy important? Level accuracy is important because it affects yield. When making a sensitivity measurement, the level accuracy of the signal generator is extremely important. For example, a particular receiver has a specified sensitivity level of -110 dBm. For this example, there are two different cases. For case 1, the source only has a +/- 5 dB level accuracy. Thus, the signal generator’s level is set to –115 dBm to ensure that all bad products are rejected. For this example, notice how 4 units failed the test that should have passed. To increase yield, a signal generator with a more accurate level is needed. For case 2, a signal generator is used that has +/- 1 dB of level accuracy specified. In this case, only 1 of the devices fails that should have passed. Case 1: Source has +/-5 dB of output power accuracy. Case 2: Source has +/-1 dB of output power accuracy. Passes test Should pass but fails Fails test Main Point: Explain that level accuracy is important because it affects test yields

39 Frequency Conversion System
What impacts level accuracy? Automatic level control (ALC) Flatness Crest factor ALC/Burst Modulator ALC Driver ALC Detector Output Attenuator from frequency conversion section The level accuracy of the signal generator varies. This variance can be attributed to the ALC parameters, the modulation bandwidth, and the crest factor of the signal Power Flatness Frequency Entire frequency range Main Point: Explain the three things that impact level accuracy are the ALC, flatness, and crest factor

40 Frequency Conversion System
How to control level accuracy? ALC/Burst Modulator For non-bursted signals Use the ALC For bursted signals Use ALC hold Use ALC hold with RF blanking Use power search Output Attenuator from frequency conversion section ALC Driver There are different ways to control the level accuracy of the signal generator. As mentioned previously, the ALC is commonly used to control the level accuracy. When the ALC is on, it is continuously monitoring and correcting the average power. For non-bursted signals, the ALC should be turned on to improve level accuracy. For bursted test signals the ALC should be used in a different way. Data that is packetized or arranged in time slots, is generally transmitted as a bursted signal. For this case, three different ALC options exist which are power search, ALC hold, and ALC hold with RF blanking. These three parameters will be discussed more in detail later. ALC Detector Main Point: Level accuracy is controlled differently for non-bursted (continuous) versus bursted signals

41 The smaller the ALC BW, the less it impacts EVM
Frequency Conversion System ALC considerations ALC/Burst Modulator ALC Driver ALC Detector Output Attenuator from frequency conversion section ALC degrades EVM Depends on loop bandwidth chosen and bandwidth of modulated signal ALC detector bandwidth smaller than what it is trying to detect, otherwise level accuracy suffers ALC BW =100 Hz The smaller the ALC BW, the less it impacts EVM ALC BW =10 kHz ALC BW =1 kHz Typically, the ALC has different loop bandwidths that can be chosen. Some common ALC loop bandwidths are listed on this slide. Since digital modulation schemes typically have some amount of amplitude modulation, such as QAM for example, the ALC will degrade the EVM some. Therefore it is suggested to use the smallest ALC bandwidth available. Since digitally modulated signals are relatively wide compared to the ALC loop bandwidth, the impact to EVM is minimal. The other bandwidths are useful for pulse modulation, without any modulation within the pulses. When using the signal generator’s pulse modulation feature, the ALC bandwidth will automatically be set. One other consideration when using the ALC is the detector bandwidth is the detector bandwidth. The detector bandwidth is fixed and cannot be modified. Thus the signal that is being transmitted should be smaller than the detector’s bandwidth. Otherwise level accuracy will suffer because the ALC will not be able to detect these power changes as accurately. This means the ALC is not able to measure (detect) all the power being delivered, so the power accuracy for wideband signals tends to be not as accurate. Amplitude Modulated signal frequency Main Point: For continuous signals use the ALC on, and use the smallest ALC loop bandwidth. EVM will be slightly degraded. The desired signal should be smaller than the detector bandwidth, otherwise level accuracy suffers.

42 Frequency Conversion System
Level control for bursted signals using the ALC Bursted signal 1 Amplitude, V time ALC on: ALC will try to correct the power of the off period RF power envelope of the bursted signal 2 Power, dBm Average power time If the test signal is bursted, a different leveling approach needs to be taken. Figure 1 is the bursted waveform that is desired to be transmitted. Figure 2 shows the RF envelope of the waveform. If the ALC were on, the ALC would try to level the off portion of the burst. The best way to level a bursted signal is to enable ALC hold. This is done by creating a marker signal and routing this to the ALC hold. The desired marker signal is shown in figure 3. When the marker signal is low, ALC hold is enabled, and the output power leveling does not respond to changes in the signal amplitude. If desired, the ALC hold can be enabled with RF blanking applied. The RF blank feature will disable the RF output during the ALC hold section, thus improving the on/off ratio of the signal. A second way to level power on a bursted signal is with the power search feature. Power search sets the power at one defined power level, and this set point is only updated during frequency or power changes. ALC hold and RF blanking cannot be used with power search. Power search is not as accurate as ALC hold because the ALC hold feature levels continuously during the on portion of the burst, and power search does not. However, the ALC requires a minimum pulse width to function. This minimum required pulse width is usually published in the data sheets. If the transmitted pulse width is less than specified by the signal generator, then power search should be used. ALC is on during this time Marker Logic level 3 ALC hold: ALC power is held for this duration Marker route to ALC hold or Pulse/RF blank Pulse/RF blank: ALC is held for this duration and the RF output is blanked, thus resulting in a greater on/off ratio time Main Point: Use the ALC hold or power search for bursted signals

43 As bandwidth increases, the more power flatness impacts level accuracy
Frequency Conversion System Power flatness affects accuracy of wideband signals As bandwidth increases, the more power flatness impacts level accuracy BW=200 MHz One other factor that affects level accuracy is the signal generator’s power flatness. This mostly affects wideband signals. This is illustrated with a graph of available power for a typical signal generator. The ALC controls the power only at a single point on this power curve. So, while the average power is still accurate for wideband signals, the power accuracy at the band edges can be very poor because of amplitude tilt or ripple in the signal generator. f1=2500 f2=2700 Main Point: Power flatness impacts the level accuracy of wideband signals. However, the rms power is still accurate, but accuracy at band edges is degraded

44 Frequency Conversion System
Flatness varies by frequency & I/Q source type Absolute level accuracy Flatness Power Entire frequency range Frequency Flatness varies according to the center frequency setting, and whether or not an internal or external IQ source is being used. Ideally it is desired to have a flat bandwidth across the entire frequency range. Even though many signal generators have level accuracy of .5 dB, this does not mean that the bandwidth is flat across the entire frequency range, as is shown on this slide. Main Point: Flatness varies according to the center frequency and the I/Q source (internal or external I/Q)

45 Average (RMS) power –23.5 dBM
Frequency Conversion System How level accuracy is impacted by the crest factor Crest factor = 10.5 dB Peak power –13 dBm Average (RMS) power –23.5 dBM The third consideration regarding level accuracy, is the crest factor of the transmitted signal. As shown in this slide, measurement of the RF envelope shows that the peak power is –13 dBm, and the average power is – dBm. This makes the crest factor 10.5 dB. To understand why crest factor affects level accuracy, the difference between RMS or average power and peak envelope power needs to be further discussed. Average power is defined as the energy transfer rate averaged over many periods of the lowest frequency in the signal. The peak envelope power represents the maximum excursion of the signal due to multiple signal components aligning in phase. Peak power is generally much higher than the average power for non-constant amplitude modulation formats such as for CDMA formats and a/g WLAN. When the ALC is on, average power is the amplitude value displayed on the front panel of most signal generators. However, when the ALC is off, the amplitude value that is displayed on the front panel of the signal generator may be the peak power or average power. Regardless of how the power is reported on the signal generator’s front display, it is still important to know the crest factor of the signal. If only the peak power is known, then the crest factor is needed to compute the average power. If the average power is known, the crest factor is needed to compute the peak power. If this information is not known, then the frequency conversion system may be underdriven leading to unrealistic distortion performance. On the other hand, the signal generator may be overdriven, leading to distortion stemming from the source itself which would cause misleading test results. Amplitude time Main Point: You need to know the crest factor of your signal, other wise you can overdrive or underdrive your device under test

46 Phase noise is expressed as jitter in the time domain
Frequency Conversion System What is spectral purity? Harmonic Spur CW signal Phase Noise Non-Harmonic Spur Amplitude Broadband noise f0 2f0 frequency Another important issue that impacts the frequency conversion system is the spectral purity of the signal generator. Spectral purity is the term used to describe how free the signal is from undesired characteristics. In this example, only the CW signal is desired. The undesired characteristics are the harmonics, non-harmonic spurs, phase noise and jitter. These characteristics degrade spectral purity. {Not to be said: added for the application note-> For more information about spectral purity see [4].} Phase noise is expressed as jitter in the time domain Amplitude time Main Point: Spectral purity is degraded by phase noise, jitter, harmonics and broadband noise

47 Frequency Conversion System
Why is phase noise important? Channel Separation Impacts ACPR tests Adjacent Channel Amplitude Phase noise frequency Blocking signal Impacts blocking tests The first spectral purity issue to be discussed is phase noise. First of all, why is phase noise important? Phase noise is important because it will impact your adjacent channel power ratio measurements and blocking tests. These measurements are illustrated in this slide. Notice that in the blocking test illustration, the desired signal is completely masked by the blocking signal’s phase noise. The phase noise of the test signal is negatively impacting the measurement results. Amplitude Desired signal Phase noise frequency Main Point: phase noise impacts ACPR and blocking tests

48 Phase noise results in rotation of the constellation
Frequency Conversion System Phase noise degrades signal quality Phase Noise I Test Signal Q Error Vector f Ideal Signal Additionally, phase noise degrades the EVM. Looking at the I/Q constellation, phase noise appears a rotation of the constellation points. For higher-order modulation formats, such as 64-QAM, the signal is more sensitive to phase noise. If the phase noise is severe enough, then bit errors can occur. RMS Constellation Phase Error Phase noise results in rotation of the constellation Main Point: Phase noise degrades in band signal quality. It can rotate your constellation points

49 Frequency Conversion System
Phase noise versus offset frequency from carrier 4 ó 10 A= B= ô - 10 - 7 C= 10 d f = 9.9 10 ô õ 2 10 7 ó 10 ô 4 -70 - 10 10 - 6 ô 10 d f = 6.868 10 A ô f B õ 4 10 10 dB/decade L(f) ,SSB phase noise (dBc,/Hz) -100 D Digital modulation on The most common and meaningful method specifying phase noise is plotting of the signal generator’s single-sideband (SSB) phase noise in a 1 Hz bandwidth versus the offset from the carrier. The SSB phase noise is expressed in dB relative to the carrier (dBc). Different sections of the phase noise plot contribute a different amount to the over all phase noise. A simple example is shown to illustrate how much each section contributes to over all phase noise. The first part of the graph, part A, is mostly dominated by the phase noise of the reference oscillator. On a log-log plot, this noise is usually modeled at a slope of 1/f3, which translates to a slope of 30 dB per decade. Part B is the contribution to the phase noise of the PLL. Part C is phase noise results from the VCO noise and the broadband noise floor. This can be modeled as 1/f2, which translates to a slope of 20 dB per decade. The bold black lines illustrates the phase noise of a CW source. When the digital modulation is switched on, typically the far out phase noise increases compared to that of the phase noise of a CW source only. When the I/Q modulator is switched on for digital modulation, the signal passes through the I/Q modulator and other components, and the CW signal bypasses these components. In this example, the broadband phase noise is modeled as 10 dB per decade to illustrate the increase in broadband noise. This is an orange dashed line. However, a real signal generator does not contribute this much phase noise. Broadband noise raises the overall noise floor, which causes interference with low-level measurements such as blocking tests. Alternate channel performance is dominated by broadband noise. The farther that you move away from the carrier frequency, the more that broadband noise is a contributing factor. Broadband noise will increase if modulation is on. Modulation is usually off for a blocking tests. The main issue to be aware of is that most signal generator’s data sheet list phase noise at one offset, using a CW signal. Additionally, showing the phase noise at one offset is not the best indicator to illustrate how much phase noise will be added to your system. It is best to look at the SSB phase noise plots. 30 dB/decade CW only -130 C -140 20 dB/decade 10 102 103 104 105 106 107 Frequency, offset from carrier Main Point: Each section of the phase noise plot contributes a different amount to the phase noise. Notice that when digital modulation is on, this increases the broadband phase noise, and this will add to the overall phase nosie

50 RMS= (  2•L(f) •df )  Frequency Conversion System
What does the source’s phase noise do to my signal? f2 RMS = RMS= (  2•L(f) •df ) radians (9.87 x °) f1 Root mean square angular deviation -70 A B L(f) ,SSB phase noise (dBc,/Hz) Test Signal -100 Error Vector To determine how much the signal generator’s phase noise will contribute to your test signal, you need to know your filter’s characteristics, such as filter type, bandwidth, filter coefficient, etc. This simple example illustrates an ideal low pass filter. Basically, the noise that falls within the filters bandwidth will contribute to your signal’s EVM. The rms phase noise can be calculated as shown using the equation on this slide. It is computed and expressed as a percentage of the square root of the mean power of an ideal signal. Depending on your design, the signal generator’s phase noise may not be an issue. However it may be for signals where the symbols are spaced close together, such as for a 64-QAM. ideal low pass filter f Ideal Signal RMS -140 10 102 103 104 105 106 Frequency, offset from carrier Main Point: To determine how much the signal generator’s SSB phase noise impacts your signal, integrate the area under the phase noise curve for the bandwidth of your filter

51 Multiple phase locked loops
Frequency Conversion System What improves phase noise performance? Multiple cascaded phase locked loops PLL’s oscillator YIG or VCO Reference oscillator TCXO or OCXO 1 phase locked loop 30 dB improvement Phase locked loop Many different signal generators are available that offer different phase noise performance. What improves a signal generator’s phase noise? A phase locked loop improves phase noise. The most basic phase locked loop starts with a reference oscillator. This reference oscillator feeds the phase locked loop, which controls the primary oscillator. The reference oscillator affects the close in phase noise performance and the primary oscillator affects the far from carrier phase noise performance. Additional PLLs can reduce the phase noise of a signal generator. This slide illustrates that the signal generator with multiple phase locked loops has 30 dB better phase noise than the signal generator with only one phase locked loop. Another design element that improves phase noise is the type of primary oscillator used in the phase locked loop. Generally, there are two types of primary oscillators available. The Yttrium-iron-garnet (YIG) oscillator has much better phase noise than a voltage controlled oscillator (VCO) oscillator. Additionally, the reference oscillator impacts the phase noise performance. The reference oscillator is generally either a temperature compensated crystal oscillators or TCXO's or oven controlled crystal oscillators ( OCXO) which are crystals that have been placed in an oven controlled environment. This environment maintains a constant temperature and provides shielding from the effects of line voltage. The OCXO is more stable than the TCXO. Frac-N Multiple phase locked loops 1 GHz Ref f Phase Detector Primary Oscillator Reference Oscillator Main Point: The signal generator’s phase noise is improved by multiple PLLs, the PLLs oscillator, and the reference oscillator

52 Distortion products contribute to ACPR
Frequency Conversion System Harmonics & non-harmonics Contributes to distortion ACPR dominated by distortion products Reported on data sheet as a single value for a particular frequency range Distortion products contribute to ACPR Harmonic and non-harmonic signals are non-random or deterministic signals that are created from mixing and dividing signals to get the carrier frequency. These signals may be harmonically related to the carrier and are called harmonics. The non-harmonic spectral line is called a spurious signal, or a spur for short. It is specified in amplitude in relation to the carrier (dBc). Harmonic & non-harmonic signals contribute to distortion. However, the harmonics can usually be filtered out before transmission, if the test signal is not swept. The non-harmonics, or spurious signals often cannot be filtered because they fall into the bandwidth of interest. A signal generator’s data sheet commonly lists the value in dBc for ALL the spurs. However, it does not list how many spurs that are generated, or if one of these spurs fall into a critical frequency range of your measurement. Some people assume that the spurs are plotted on the SSB plot but they are not. Main Point: harmonics and non harmonics contributes to distortion. Harmonics & non-harmonics are not plotted on the SSB phase noise plot

53 Frequency Conversion System
Why is bandwidth important? BW m 3rd order spectral regrowth 5th order spectral regrowth Amplified 4 carrier W-CDMA 20 MHz 60 MHz 100 MHz Another factor that impacts measurement results, is the bandwidth of the signal. Modern communication signal bandwidths are becoming wider. The channel bandwidth for AM is 10 kHz, for FM is 200 kHz, for W-CDMA is 5 MHz, and b is 25 MHz. When performing tests, you not only want to test the in-band test signals, but the interferers in-band, out-of-band, and out-of-channel. Rapid frequency hopping can be simulated within the wide modulation bandwidth by generating waveforms with multiple preset frequency offsets. Wide bandwidth gives you the ability to add multiple carriers to simulate a system that is loaded to capacity. This is important to determine how your receiver will operate under fully loaded conditions . Thus you usually want a signal generator with wide bandwidth. This example shows a common wideband signal that is used to test W-CDMA multi-carrier power amplifiers. The bandwidth required to transmit the 4 carriers is 20 MHz. Additionally, it is desired to transmit the 3rd and 5th order distortion products to provide a realistic test signal. This requires a total bandwidth of 100 MHz. The BW of the transmitting signal generator should be 3 to 5 times the desired signal’s BW to accurately represent the 3rd order and 5th order products of the signal. Example: enough bandwidth to transmit 3rd , 5th order distortion products for a 20MHz wide 4 carrier W-CDMA signal = 100 MHz Main Point: You need enough bandwidth to transmit the desired signal, as well as 3rd and 5th order distortion products

54 Frequency Conversion System
What is bandwidth? Baseband bandwidth RF bandwidth Amplitude -20 MHz 0 Hz +20 MHz frequency 3 dB bandwidth What limits the signal generator’s bandwidth? Both the baseband generator and the IQ modulator have a certain amount of bandwidth, and they are usually not the same. Because IQ modulation is used in a vector signal generator, negative frequencies exist at baseband, as illustrated on this slide. When the baseband frequency is translated RF, the bandwidth is twice that of the baseband bandwidth. A vector signal generator’s bandwidth can be listed many ways on the data sheet, and the terminology can vary. Bandwidth is typically described as the frequency at which an instrument's amplitude response has declined by some set amount, usually listed 1 or 3 dB, from the response at the center frequency. However, how do you know if the data sheet is describing the baseband bandwidth or the RF bandwidth? Baseband designers are interested in the bandwidth of the baseband generator. The baseband bandwidth is usually not explicitly stated on the data sheet, but the bandwidth can be determined from the sampling rate. The sample rate is the frequency that the DAC samples the input digital signal and produces an analog output. The sampling rate can be divided by 2.6 to determine the baseband bandwidth available. This fulfills Nyquist’s rule, as well as providing some guard band for the roll-off of the reconstruction filter. RF designers are usually interested in the RF bandwidth of the signal generator. A signal generator’s specification for RF bandwidth can be misleading because it may listed in different ways, such as I/Q modulator bandwidth, external or internal I/Q bandwidth, or simply RF bandwidth. Sometimes bandwidth is expressed as using the internal IQ signals from the built-in baseband generator, or external analog IQ signals from an independent baseband generator. Fundamentally, the maximum bandwidth of the source is usually limited by the IQ modulator. Usually the vector signal generator’s IQ modulator receives its’ input signal from the internal baseband generator. Many signal generators allow the built-in baseband generator to be bypassed, and analog IQ inputs from another baseband generator to be applied directly to the IQ modulator. By driving the external IQ modulator inputs with an external I/Q source, a much wider bandwidth can usually be obtained. The external baseband generator should have a higher clock rate than the internal baseband generator. 40 MHz occupied bandwidth Main Point: Bandwidth is confusing,. Different signal generator companies list bandwidth in different ways. What is my baseband bandwidth, and what is my RF bandwidth?

55 Baseband System Agenda Baseband system test considerations Overview
Frequency conversion section Baseband section Amplification section Overview System functionality test and troubleshooting Amplifier test Frequency conversion system test considerations Baseband system test considerations Summary RF system The last section to be discussed is the baseband section. This section covers what issues need to be considered when testing a baseband device. RF system Frequency conversion section Amplification section Baseband section Main Point: Transition slide to the baseband system test considerations

56 Mechanical connection Stimulus requirements
Baseband System What is needed from the test equipment? 3 Clock source Sample clock 4 Data format ADC FPGAs, DSPs, & ASICS ADC Memory 5 Bus configuration Every new project brings its own demands for different types of baseband devices with different operating parameters. Each device has different requirements for interfaces. When choosing test equipment to test your baseband device there are 6 different parameters that should be considered. The first parameter is the stimulus. In this example, the FPGA is being tested. What type of stimulus or test patterns should be used access the FPGA’s performance? Is it okay to use a simple test pattern, or is a more complex signal required? A simple pattern can not test the FPGA’s decoding algorithms. The second item to consider is how to mechanically connect the test equipment to the FPGA circuit. The mechanical connector from the test device has to match the FPGA to provide a good physical connection. The third consideration is how is the device going to be synchronized with the test equipment? What if a clock source is not available from the FPGA, can the test equipment’s clock be used instead? Fourth, what is the data format required for the FPGA? Some FPGAs require digital data formatted with 2’s complement, others with binary offset, some 12-bit words, other 16 bits. Is the test equipment able to generate this data format? Another consideration is what type of bus configuration is required? You may need to transmit data over a serial or a parallel bus to test the FPGA. Lastly, the test equipment should create the proper electrical and voltage signals to match the logic type of the FPGA. 2 Mechanical connection 6 Logic type 1 Stimulus requirements Main Point: What do I need to think about when selecting the test equipment for my digital baseband section?

57 Mechanical connection
Baseband System Stimuli provided by various baseband generators Function generator simple test stimulus sinusoid, ramp, pulse, triangle Pattern generator pseudo-random bit patterns custom data pattern Waveform generator Complex “real-world” test stimulus Mechanical connection Bus configuration Logic type Sample clock FPGAs, DSPs, & ASICS ADC Clock source Data format 2 6 5 4 3 Memory 1 Stimulus requirements The first consideration to be discussed is what type of stimuli is needed. Different baseband generators produce different types of stimuli. The three basic types of baseband generators that are available are function generators, pattern generators, and waveform generators. A function generator can only provide simple test signals such as a sinusoid, ramp, pulse, and triangle waves. These waveforms do not represent a realistic type of test signal that a digital device that uses digital modulation will encounter. Additionally, a function generator typically provides simple analog outputs, which will not interface easily with a digital device. The next generator is the pattern generator. This type of generator provides bit patterns and custom data patterns. Digital designs engineers have traditionally used a pattern generator to perform digital functionality test. These tests only verify whether the digital implementation works as intended. Simple data patterns are not sufficient to realistically represent a complex modulated format with various peak-to-average ratios. As digital communications systems advance, the modulation and access schemes are becoming more complex. The simple signal that function generators and pattern generators provide do not give the same results as the actual “real-world” test signal. Thus a baseband generator that creates this type of stimuli needs to be used. The waveform generator is capable of creating complex stimuli. This type of baseband generator is popular with RF designers, and is gaining more popularity with baseband designers. Given the complexity of today’s radio systems, designers need to verify more of the end-user performance at the baseband design phase than has been traditionally done. This test approach enables the designer to test the baseband device in complex environments in which baseband systems must operate. Baseband designers who test with a complex stimulus, determine early in the design cycle where the device can fail when operating in a radio. For example, a common design problem for communications DACs is headroom. If the DAC is tested with a high-stress, multi-channel radio signal, you can see what power levels will overextend your DAC range to cause clipping. Or if you test WLAN chipsets, you can now verify at baseband that this section can correctly decode WLAN frames before the frequency conversion system is developed. A coded baseband signal is needed to generate the test signal used in the final configuration. Additionally, if you are performing receiver tests, you will need the correct amount of encoding applied to the signal to enable BER and PER measurements to be performed. Main Point: 3 common types of stimuli, simple functions for function generator, simple patterns from pattern generator, or real world complex stimuli from a waveform generator

58 Baseband System Waveform generators Two types of waveform generators
Real-time generation Two types of waveform generators Real-time baseband generator Arbitrary waveform generator (AWG or arb) Waveform generated Waveform played in real-time Waveform generation with an arb Two different types of waveform generators are available. The first type of waveform generator is the real-time baseband generator. The real-time baseband generator creates and processes signals in real-time. The waveforms created by this type of generator are unconstrained by signal generator memory limitations. The signals are not stored in memory; they are continually generated and transmitted. Whether one or one million frames are needed, the signal is always continuously created, with no repetition of the data fields. This allows seamless data sequences for BER tests. The real-time signal is updated immediately when signal parameters are changed, and you don’t have to wait for the signal to be rebuilt. The types of waveforms available for a real-time baseband generator are specific to wireless communication’s standards, with fixed data framing. However, there is usually a custom mode available. The custom mode gives you access to the baseband generators symbol builder, FIR filters, and various data parameters. Some disadvantages are custom framing is not available, and you are limited to the signal creation software provided for this type of generator. Additionally, the real time generator cannot create as many carriers, and can only create a limited number of channels. The second type of waveform generator is the arbitrary waveform generator. With the arb, the waveform can be more complex. The arb is used to simulate wide bandwidth multicarrier signals containing hundreds of channels, add impairments, and vary parameters between the carriers. Additionally, you can use general purpose software to create custom waveforms to be downloaded to the arb. Some disadvantages of the arb the waveform is not created instantaneously like that with the real-time generator. Waveform build time depends on the complexity of the waveform. Another disadvantage is that the data is not continuously distributed across the payload portion of the frames. This is an issue with BER tests, when the BER analyzer expects a non-truncated data sequence. Compact disc Waveform generated Waveform stored to memory Waveform played back from storage medium Main Point: Two types of waveform generators: real-time and arb. Pros and cons of real-time generator versus the arb

59 Baseband System Waveform generator hardware considerations
frequency Amplitude Bandwidth wide enough to transmit: desired signal 3rd and 5th harmonics Waveform play back memory Enough to play back desired signal Waveform storage memory Large enough to conveniently store your test signals When deciding which waveform generator to use, you will need to consider parameters such as bandwidth and memory depth. The baseband bandwidth needs to be large enough to transmit the desired signal, as well as the 3rd and 5th harmonics. The playback memory and bandwidth needs to be large enough to adequately play back the test signal. Playback memory if frequently expressed as memory depth, or volatile memory, in units of mega samples. Sometimes the available memory is expressed in bytes, or bits. To compute the number of bytes for the play back memory, you need to know how many bits are represented for each sample point. For example, if a sample point consists of 16 bits for I and 16 bits for Q and 8 bits for the marker, then one sample point equals 40 bits, or 5 bytes. If you are creating your own test signal for the arb, you will need to know how many bits are represented by each sample point to ensure you have enough memory on your signal generator. If the baseband generator’s volatile RAM is not sufficient to playback your test signal, then waveform streaming can be used. This enables allows you to stream a waveform directly off a PC’s hard drive, and your memory is limited by the PC’s hard drive and not your baseband generator. The last consideration is available non-volatile memory available for waveform storage. A library of waveforms can be stored to the waveform storage memory, which is usually a hard drive inside the signal generator. This enables you to quickly recall your waveforms at a touch of a few buttons, instead of re-creating them. Main Point: hardware considerations when selecting your baseband generator: bandwidth, playback memory, and waveform storage memory

60 Baseband System Signal creation software considerations
Waveform signal creation Commercially available software Create your own waveform Frame header Payload Preamble Sync Word Trailer Payload header CRC Address Type Length ACK NACK FEC Signal creation software is available for both types of waveform generators. The waveform generator can generate a complex waveforms that emulate real world test signals. There are basically two ways to a waveform is created for the baseband generator. One way to create a waveform is to use a commercial signal creation software package. This software is usually provided by the waveform generator vendor to create a specific type of test signal. Usually these test signals are based on popular wireless communication standards such as W-CDMA or WLAN and many others. The advantages of this approach is that the software is generally easy to use and conforms to known standards. Plus, you save time from having to build your own standards-based waveform. The disadvantages to this choice is that this software is typically for a single purpose, which makes it inflexible for using the same software to create other waveforms. Additionally, the standards-based waveforms can be implemented to varying degrees. For example, the software may not provide the level of channel coding that you require for your specific test. Alternatively, you can use a general purpose software package such as C, Visual basic, or Matlab to create your own waveforms. These waveforms can only be used with the arbitrary waveform generator or arb. More about the arb will be discussed below. The advantages are that this gives you more flexibility and control over what level of implementation is incorporated. Additionally, general purpose software can be used to create any type of waveforms, and they do not have to comply to any particular wireless communication standard. The disadvantages are that it may take a long time learn how to use the general purpose software and time to interpret and read through the wireless communication’s standard. This lost time results in a longer time to market for your device. Main Point: How do I create a waveform. Should a commercially available software package be purchased, or should I create my own using C++?

61 Baseband System Test the baseband system with a complex stimulus
Transmitter test Vector signal generator Baseband section Test the baseband system with the same complex stimulus used by the RF system Identify baseband problems before RF integration Avoid costly rework Reduce uncertainty Use same test equipment for baseband & RF tests RF system Digital inputs Frequency conversion section Amplification section Receiver test Vector signal generator Complex digitally modulated test signals are available on RF and MW vector signal generators.These type of test signals are traditionally used to test the RF system of the radio. So why use a signal generator to test the baseband system. These complex test signals are also needed to test the baseband system to ensure that the baseband device will pass the RF tests. A common problem that designers experience is that the baseband device tests okay with a pattern generator, and the RF system tests okay with a signal generator, but the integrated product fails the same RF test. The baseband system can be tested independent of the radio’s RF system. A vector signal generator can accept digital inputs and can substitute for the transmitter’s RF system. This test solution enables transmitter designers to test the baseband section at RF and to identify problems such as low EVM or clipping, early in the design process. Alternatively, baseband receiver designers can use the vector signal generator to test the decoding algorithm of the baseband system. The vector signal generator can provide either digital IQ and digital IF outputs to the digital baseband system. Finding design issues early in the design process prevents costly rework later. Additionally, using the same signals for the baseband and RF phases of the design cycle reduces design uncertainty. When selecting test equipment to test your digital baseband design, there are many issues to consider, and these will be discussed in this section. Baseband section RF system Frequency conversion section Amplification section Digital outputs Main Point: The baseband generator should be tested with the same complex signal that is used to test the RF section. This will help avoid costly rework of the baseband section.

62 PRBS signal (supplied by pattern generator)
Baseband System Complex stimulus versus PRBS W-CDMA test signal PRBS signal (supplied by pattern generator) 18 dB crest factor! As shown in this CCDF curve, a complex stimulus has different power characteristics than the pseudo-random binary sequence (PRBS) signal provided by a pattern generator. An actual communications signal, such as W-CDMA, has a different crest factor than random test patterns. If only a simple pattern generator is used for testing the digital baseband section, then problems can arise during the RF integration stage. you may have some unexpected performance issues that could result in expensive rework and more troubleshooting. Main Point: A simple pattern generator does not provide a realistic signal, like that of a a complex stimulus. If a simple pattern is used to test the baseband section, it may fail tests when it is integrated into the RF system.

63 Stimulus requirements
Baseband System Data integrity Bus configuration Logic type Stimulus requirements Sample clock FPGAs, DSPs, & ASICS ADC Clock source Data format 1 6 5 4 3 Memory 2 Mechanical connection Mechanical connection Short interconnect Variety of break-out-boards Vector signal generator Digital outputs Baseband section The key criteria for the signal stimulus has been identified. Next, the data integrity of the signal will be discussed. Data integrity is ensured by the mechanical connection from the test equipment to the device under test. The cable between the digital output from the test equipment and the tested device should be short so that cross talk is not a problem. Additionally, a variety of break out boards are desired, to reduce the amount of customized fixtures. With a variety of break out boards, you can choose a connector that is most similar to your type of device. Variety of break-out boards Short interconnect cable Main Point: The data integrity is dependent on good mechanical connection from the test equipment to the DUT. The cable should be short and the test equipment should provide multiple break out boards so you don’t have to waste time doing customization

64 Mechanical connection Stimulus requirements
Baseband System Flexible clocking 3 Clock source Clock source Provides timing between clock & data Need to adjust for any skew Need a variety of clock sources available From device under test, test equipment, or other clock source Mechanical connection Bus configuration Logic type Stimulus requirements Sample clock FPGAs, DSPs, & ASICS ADC Data format 1 2 6 5 4 Memory Data after Data before Clock To synchronize your devices, you need a common clock. The clock source should be adjustable to correct for any skew between the data and clock. Other wise the data will not be sampled correctly. An adjustable skew is needed so that you can meet sample and hold criteria of your device. You need to align the clock edges to the valid portion of the data that is being sampled. Skew adjustments are needed to meet sample and hold criteria of device Main Point: A flexible clocking source is needed to adjust for any skew between the data and clock. A variety of clock sources are needed in case future tests need them

65 Stimulus requirements
Baseband System Adaptability Data format 2’s complement, offset binary, 4-16 bit word size, MSB, LSB Bus configuration Serial, parallel Logic type TTL, CMOS, LVDS Configurable test equipment Flexible enough to test current & future designs 4 Stimulus requirements Sample clock FPGAs, DSPs, & ASICS ADC Clock source 1 3 Memory Data format 5 Bus configuration 6 Logic type Data standards, data formats, bus configurations, and logic types will vary for each baseband device that is tested. When selecting a baseband generator to test your digital devices, ensure it has a variety of data formats and electrical interfaces so that it is adaptable enough to meet your current, and future digital test needs. This amount of configurability on the test equipment saves you time from building adapters and converters for each new project. Main Point: You want configurable test equipment that is flexible. You want to be able to easy change the data format, bus configuration, and logic types

66 Conclusion Summary Optimizing the Stimulus to Maximize System Performance Realistic stimulus helps to ensure your radio will work in in its operating environment Stimulus requirements have changed for amplifiers Traditional specifications are different for digital modulation Digital baseband system needs a complex stimulus Agilent has flexible test equipment to meet all your stimulus needs To summarize, increased digitization of the transceiver has changed how testing is done. Digital radios require a complex stimulus that exercises the full range of environmental and signal conditions. Additionally, increased signal complexity has changed the stimulus requirements for amplifier testing. The amplifier needs to be stimulated with a realistic test signal with the correct power characteristics. Moreover, the signal generator’s analog specifications behave differently when digital modulation is turned on. These differences need to be understood so that the proper signal generator is selected and the test results are properly interpreted. Furthermore, simple digital stimulus is not adequate for baseband tests. A complex digital stimulus helps you to find design problems before the RF integration stage. When choosing a stimulus to test the digital radio, it is important to understand how the signal stimulus specifications affects the performance of the radio system. Otherwise, differences between the stimulus you are using, and the stimulus that other groups of people are using may differ enough to cause unexpected measurement results, and possible product failure. Main Point: Summary: To close you want a realistic stimulus for every section of the radio, otherwise you may get unexpected measurement results

67 Agilent’s Vector Signal Generators
RF and Microwave Vector Signal Generation E4438C ESG Vector signal generator Frequency to 6 GHz Bandwidth up to 160 MHz E8267C PSG Vector signal generator Frequency up to 20 GHz Bandwidth up to 1 GHz For Further Information More information can be found at the following web site: or Main Point: Our main vector signal generators: high frequency range and bandwidth

68 Agilent Baseband Studio
N5110A Baseband Studio for waveform streaming Virtually unlimited playback memory N5115A Baseband Studio for fading Optimize number of paths versus bandwidth Up to 48 paths or 30 MHz bandwidth N5102A Baseband Studio digital signal interface module Digital I/Q & digital IF output Extremely flexible For Further Information: studio More information can be found at the following web site: Main Point: Product slide for Baseband Studio. Streaming offers unlimited playback memory. Baseband Studio for fading enables you to trade off bandwidth for number of paths. The digital signal interface quickly and easily enables you to get digital IQ or IF from your vector signal generator

69 Thank You for Attending
Main Point: Thank the audience and accept questions

70 Main Point: Reference section.
[1] “RF Source Basics”; CD # EE [2] “Digital Modulation in Communications - An Introduction”; application note 1298:  # E [3] “Characterizing Digitally Modulated Signals with CCDF Curves”; application note: # E [4] “Agilent Signal Generator Spectral Purity”; application Note 388: # Main Point: Reference section.

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