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KavoshCom Asia R&DApril 9, 2007 1 WiMax RF chip Design Ali Fotowat, PhD. Managing Director KavoshCom Asia R&D April 9, 2007.

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Presentation on theme: "KavoshCom Asia R&DApril 9, 2007 1 WiMax RF chip Design Ali Fotowat, PhD. Managing Director KavoshCom Asia R&D April 9, 2007."— Presentation transcript:

1 KavoshCom Asia R&DApril 9, WiMax RF chip Design Ali Fotowat, PhD. Managing Director KavoshCom Asia R&D April 9, 2007

2 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way. Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

3 KavoshCom Asia R&D April 9, 2007 Issues

4 KavoshCom Asia R&D April 9, 2007 Issues

5 KavoshCom Asia R&D April 9, 2007 Issues

6 KavoshCom Asia R&D April 9, 2007 Wireless Technologies (source: Worldwide Interoperability for Microwave Access Forum)

7 KavoshCom Asia R&D April 9, 2007 Wireless Standards Mobility vs. User/Link Bit rate Mbps

8 KavoshCom Asia R&D April 9, 2007 WIMAX stands for Worldwide Interoperability for Microwave Access WiMAX refers to broadband wireless networks that are based on the IEEE standard, which ensures compatibility and interoperability between broadband wireless access equipment WiMAX, which will have a range of up to 31 miles, is primarily aimed at making broadband network access widely available without the expense of stringing wires (as in cable-access broadband) or the distance limitations of Digital Subscriber Line. What is WiMax?

9 KavoshCom Asia R&D April 9, a Uses the licensed frequencies from 2 to 11 GHz Supports Mesh network b Increase spectrum to 5 and 6 GHz Provides QoS( for real time voice and video service) c Represents a 10 to 66GHz d Improvement and fixes for a e Addresses Mobile needs Enable high-speed signal handoffs necessary for communications with users moving at vehicular speeds IEEE Specifications

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12 KavoshCom Asia R&D April 9, 2007 Point to Point BACKHAUL INTERNET BACKBONE Telco Core Network or Private (Fiber) Network Non Line of Sight Point to Multi- point FRACTIONAL E1/T1 for SMALL BUSINESS E1/T1+ LEVEL SERVICE ENTERPRISE Backhaul for Business

13 KavoshCom Asia R&D April 9, 2007 INTERNET BACKBONE Telco Core Network or Private (Fiber) Network Non Line of Sight Point to Multi- point OUTDOOR CPE INDOOR CPE Point to Point BACKHAUL & Consumer Last Mile

14 KavoshCom Asia R&D April 9, 2007 INTERNETBACKBONE Telco Core Network or Private (Fiber) Network Non Line of Sight Point to Multi-point e e SEEKS BEST CONNECTION Laptop Connected Through e 2 to 3 Kilometers Away Line of Sight BACKHAUL PC Card e Nomadic / Portable

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16 Issues

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19 Adaptive Modulation

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22 Issues

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27 Tolerance to Multipath and Self- Interference Scalable Channel Bandwidth Orthogonal Uplink Multiple Access Support for Spectrally-Efficient TDD Frequency Selective Scheduling Fractional Frequency Reuse Fine Quality of Service (QoS) Advanced Antenna Technology Key Advantages of Mobile WiMax to 3G

28 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

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32 KavoshCom Asia R&D April 9, 2007 Issues

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34 The shared channel concept

35 KavoshCom Asia R&D April 9, 2007 Key ideas in HSDPA The HSDPA concept is based on the following features: Shared channel transmission Higher-order modulation Short transmission time interval (TTI) Fast link adaptation Fast scheduling Fast hybrid automatic-repeat-request (ARQ).

36 KavoshCom Asia R&D April 9, 2007 Reduced latency Short TTI (Transmission time interval) Channel codes from the shared code resource are dynamically allocated every 2 ms or 500 times per second. A short TTI reduces roundtrip time and improves the tracking of channel variations—a feature that is exploited by link adaptation and channel- dependent scheduling.

37 KavoshCom Asia R&D April 9, 2007 Code sharing for shared channel Shared channel transmission HS-DSCH is based on shared-channel transmission, which means that some channel codes and the transmission power in a cell are seen as a common resource that is dynamically shared between users in the time and code domains. The shared code resource onto which the HS-DSCH is mapped consists of up to 15 codes. The spreading factor (SF) is fixed at 16.

38 KavoshCom Asia R&D April 9, 2007 Issues

39 KavoshCom Asia R&D April 9, 2007 Increase average speed by serving channels that can be best served!!

40 KavoshCom Asia R&D April 9, 2007 Issues

41 KavoshCom Asia R&D April 9, 2007 Issues QPSK, 16QAM

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43 KavoshCom Asia R&D April 9, 2007 Hybrid Automatic Repeat Request

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45 KavoshCom Asia R&D April 9, 2007 HSDPA Mutli-User Diversity Efficient scheduler High data rate Low data rate

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47 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

48 KavoshCom Asia R&D April 9, 2007 Transmitter test set-up

49 KavoshCom Asia R&D April 9, 2007 Transmitter requirements (IEEE , 8.5.2) Transmit power level control Transmit spectral flatness Transmit constellation error Transmit spectral mask ACPR, maximum output power, spurious and harmonics are also important

50 KavoshCom Asia R&D April 9, 2007 Transmitter Spectral Flatness Spectral linesSpectral flatness Spectral lines from -50 to -1 and +1 to +50 +/--2 dB from the measured energy averaged over all active tones Spectral lines from -100 to -1 and +1 to dB/--4dB from the measured energy averaged over all active tones Adjacent subcarriers+/--0.1dB

51 KavoshCom Asia R&D April 9, 2007 Burst typeRelative constellation error (dB) BPSK-1/ QPSK-1/ QPSK-3/ QAM-1/ QAM-3/ QAM-2/ QAM-3/ Transmitter Constellation Error

52 KavoshCom Asia R&D April 9, 2007 Receiver test set-up

53 KavoshCom Asia R&D April 9, 2007 Receiver requirements are defined in IEEE section Receiver sensitivity Receiver adjacent and alternate channel rejection Receiver maximum input signal Receiver maximum tolerable signal Receiver image rejection

54 KavoshCom Asia R&D April 9, 2007 Modulation type and coding rateBandwidth 64QAM16QAMQPSKBPSK 3/42/33/41/23/41/ MHz 3.5MHz 7.0MHz 10.0MHz 20.0MHz Rx SNR (dB) Receiver Sensitivity (dBm) for 10e-6 BER

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56 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

57 KavoshCom Asia R&D April 9, 2007 Almost all of the implementations use Direct Conversion method Direct Conversion pros and cons: Advantages: 1.High level of integration 2.Low power consumption Disadvantages: 1.DC offset problem 2.Higher flicker noise 3.Poor quadrature matching Examples of Implementation Trials

58 KavoshCom Asia R&D April 9, 2007 For WLAN / WiMAX [B. Farahani-05] Direct Conv Architecture

59 KavoshCom Asia R&D April 9, 2007 Frequency Synthesizer Specifications [B. Farahani-05] 1.The phase noise requirement for PLL : offset frequency 2.The settling time should be better than: 5µs Direct Conv Architecture

60 KavoshCom Asia R&D April 9, 2007 Block Requirements for Direct Conversion WiMAX Receiver [B. Farahani-05]

61 KavoshCom Asia R&D April 9, 2007 Block Requirements for Direct Conversion WiMAX Receiver [B. Farahani-05]

62 KavoshCom Asia R&D April 9, 2007 Different signal levels in Zero-IF receiver for WiMAX system [B. Farahani-05]

63 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

64 KavoshCom Asia R&D April 9, 2007 Good idea to support both WiMax and WLAN WiMAX needs are more stringent than WLAN: 1.Tx EVM requirement is smaller for WiMAX 2.Because of Higher number of subcarriers in WiMAX OFDM, Phase noise of the VCO should be smaller for WiMAX which is on the order of 1 ˚ at arbitrary channel centers 3.I/Q sideband rejection requirement is more stringent than WLAN which is of the order of 35dB. 4.To cover different BW in WiMAX, programmable analog channel selection filters are required

65 KavoshCom Asia R&D April 9, 2007 Multi-band RF front-end for 4G WiMAX and WLAN applications [C.Garuda-06] 1.Direct Conversion Receiver 2.Multi band including: GHz, GHz, GHz 3.Two stage & programmable LNA instead of wideband LNA 4.The gain of dB approximately constant for all bands 5.Utilizes Gilbert cell as a mixer 6.No report about synthesizer and filters 7.In 1.8v IBM 0.18µm CMOS process.

66 KavoshCom Asia R&D April 9, 2007 Two stage wide-band programmable LNA

67 KavoshCom Asia R&D April 9, 2007 Performance summary

68 KavoshCom Asia R&D April 9, 2007 Dual-band GHz, GHz, 0.18µm CMOS Transceiver for a/b/g and d/e(WiBro) [I.Vassiliou, et.al, Broadcom-06] 1.Direct Conversion double band transceiver is fabricated in a 0.18µm 1P6M CMOS 2.Fractional-N synthesizer achieves 0.6˚(0.7˚) integrated phase error at 5GHz (2.4GHz) 3.Digital calibration eliminates I/Q mismatch and carrier leakage 4.Programmable BW filters are used 5.Achieves EVM of -35dB in both transmit and receive paths 6.Achieves sideband suppression better than 45 dB & LO leakage lower than -30dBc

69 KavoshCom Asia R&D April 9, 2007 System Architecture uses TDD

70 KavoshCom Asia R&D April 9, 2007 GM-C filter and its OTA enable continuous tuning either 2-15 MHz or 10-25MHz

71 KavoshCom Asia R&D April 9, 2007 Programmable RF amplifier

72 KavoshCom Asia R&D April 9, 2007 Rx EVM vs. input power for different bands

73 KavoshCom Asia R&D April 9, 2007 Measured performance summary

74 KavoshCom Asia R&D April 9, GHz Dual-Mode WiMAX/WLAN Direct Conversion Receiver [Y. Zhou, Instit. for Infocom Res-06] 1.Direct Conversion architecture 2.The dual-mode receiver is fabricated in a 0.25µm IBM BiCMOS6HP SiGe process 3.The frequency synthesizer uses VCO running at half the RF frequency to help reduce dc offset due to LO feedthrough 4.DC offset calibration is performed on chip 5.The receiver employs GM-C base-band filter with tunable cut-off frequency of either 5 or 10 MHz 6.The chip adopts a 3 wire serial bus interface to control all the functions 7.The chip consumes 360mW from 3V power supply 8.Two mode double gain LNA is used

75 KavoshCom Asia R&D April 9, 2007 VCO with Auto Calibration Circuit 1.Frequency fine tuning is achieved by hyper-abrupt varactor 2.An auto calibration circuit is implemented to select the appropriate band based on process variations

76 KavoshCom Asia R&D April 9, 2007 Performance Summary

77 KavoshCom Asia R&D April 9, 2007 Old article but explains the integration problems A 2.4GHz Direct Conversion Transmitter for Wimax Applications, C. Masse, Analog Devices

78 KavoshCom Asia R&D April 9, 2007 The I & Q analog baseband Signal Generation Dual 14-bit DAC IQ modulator.direct up-conversion at the RF frequency remove the alias at multiples of the sampling frequency Low-pass Filters external fractional-N synthesizer LO (a continuous signal with minimal Phase error) VGA with about 50dB of gain control range. amplify or attenuate the composite RF signal out of the modulator Precise output power control is achieved. RMS power detector

79 KavoshCom Asia R&D April 9, 2007 A direct up-conversion architecture is attractive because: 1.Wimax OFDM has no active sub-carrier at the origin, direct up- conversion produces less mixing product spurs 2.Requires fewer filters which is important when dealing with such wideband signals 3.The lower number of parts helps minimize the current consumption.

80 KavoshCom Asia R&D April 9, 2007 Performance Summary WiMax OFDM modulation used here is a10MHz, 64QAM, 256-OFDM signal

81 KavoshCom Asia R&D April 9, 2007

82 A CMOS transmitter front-end with digital power control for WiMAX e applications Y.H. Liu, H.C. Chen

83 KavoshCom Asia R&D April 9, 2007 VGA First Stage of VGA: The gain control is realized with a current steering structure Second Stage of VGA: The primary coil of the on-chip transformer serves as the load inductor for a differential-to-single-ended conversion Totally: 16 gain steps are achieved

84 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

85 KavoshCom Asia R&D April 9, 2007 Complexities in Quadrature signal generation for OFDM Transmitters and Receivers What is Quadrature Modulation? First-Order Error Sources Individual Effects of error sources Proposed New Calibration Procedure Slides in this section based on Dr. Earl McCune’s presentation

86 KavoshCom Asia R&D April 9, 2007 Quadrature Modulator Converting the quadrature modulation equation as a block diagram gives the familiar form

87 KavoshCom Asia R&D April 9, 2007 Realistic QM Model There are nine different first-order error terms

88 KavoshCom Asia R&D April 9, 2007 Realistic QM Math Gain mismatch & Quadrature error Carrier leakages Data leakages DC offsets

89 KavoshCom Asia R&D April 9, 2007 ‘Ideal’ Error Values

90 KavoshCom Asia R&D April 9, 2007 Individual Error Analyses Modulation offsets Carrier Offsets Modulation gain errors Carrier magnitude errors LO quadrature error Modulator output compression

91 KavoshCom Asia R&D April 9, 2007 Standard - Use SSB Case A simple, constant- envelope signal (LSB is shown)

92 KavoshCom Asia R&D April 9, 2007 Modulation (I,Q) Offsets Cause carrier leakage AM also results

93 KavoshCom Asia R&D April 9, 2007 Carrier Offsets No effect on RF spectrum data leakage present amplitude variations on output signal

94 KavoshCom Asia R&D April 9, 2007 Modulation Gain Errors Causes image sideband AM at double the ‘data’ frequency

95 KavoshCom Asia R&D April 9, 2007 Carrier Magnitude Errors Carrier magnitude mismatch - looks identical to IQ gain mismatch

96 KavoshCom Asia R&D April 9, 2007 LO Quadrature Error Causes image sideband AM is phase shifted from gain-mismatch cases

97 KavoshCom Asia R&D April 9, 2007 Output Compression P1dB effect on QM output adds intermodulation sidebands gain mismatch casedata leakage case

98 KavoshCom Asia R&D April 9, 2007 Proposed CAL Procedure Minimize interactivity among adjustments Based on simple SSB signal Five steps (in order!): –null data leakage –null carrier leakage –zero quadrature error –match path gains –set signal level (for signals with AM)

99 KavoshCom Asia R&D April 9, 2007 Error-Combination Case data leakageRF signal

100 KavoshCom Asia R&D April 9, Ideal Modulator Drive Begin with ideal modulator SSB drive signals

101 KavoshCom Asia R&D April 9, Null Data Leakage Zero the carrier offset terms O C and O S data leakageRF signal

102 KavoshCom Asia R&D April 9, Null Carrier Leakage Adjust data offsets tradeoff until carrier is nulled RF signal

103 KavoshCom Asia R&D April 9, Minimize Image Sideband Adjust quadrature error image sideband minimizes at  e = 0 may need 0.1 dB resolution RF signal

104 KavoshCom Asia R&D April 9, Match Path Gains Adjust one data-gain term (choose A I, for example) null the image sideband compression distortion also disappears RF signal

105 KavoshCom Asia R&D April 9, Set Overall Gain Apply I(t) and Q(t) for an envelope-varying signal Turn down gains A I and A Q together to drop sidebands effects a backoff from the P1dB of the summer

106 KavoshCom Asia R&D April 9, 2007 Limited-Access Bounds Ex. : quad error limitation (no access to quadrature error) If full access to all error terms is not available, then the achievable performance will be limited. 1 degree2 degrees

107 KavoshCom Asia R&D April 9, 2007 Conclusions Quadrature modulation is a rectangular (Cartesian) method of implementing signals Real Quadrature-Modulators are not as simple as the textbooks (or databooks!) claim Quadrature modulators can be tamed if all ports are available to the design engineer Output Noise Figure is a major problem Linear modulations tend to require large output (and input) backoffs All error terms are, in general, functions of temperature!

108 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

109 KavoshCom Asia R&D April 9, 2007 How much spur rejection is needed?  For 45 dB rejection, the gain matching should be better than 0.1 dB and the phase matching better than 0.5 degree.  Some manufacturers require better than 55 dB for individual blocks!

110 KavoshCom Asia R&D April 9, 2007 Strong and weak duo A St cos(w St t) + A We cos (w We t) A two tone signal in time domain.

111 KavoshCom Asia R&D April 9, 2007 A quadrature transmitter overall block diagram

112 KavoshCom Asia R&D April 9, 2007 Transmitter features 1. Allow offset adjustment blocks at the inputs 2.A programmable low pass filter corner frequency for all WiMax needs 3.Baseband gain with  G adjustment (1 dB range in 0.1 dB resolution) 4.Control on the local oscillator phase (3 degree range with 0.1 degree control) 5.A very linear transmit mixer 6.A very linear combiner 7.A programmable attenuator (20 dB range in 1 dB steps) 8.An integrated power level detector

113 KavoshCom Asia R&D April 9, 2007 Strong and weak duo is not a duo! f Strong 3 rd Harmonic Weak 3 rd Harmonic Undesired sideband Desired sideband LO feed- through A typical shape of spectrum out of a quadrature transmitter

114 KavoshCom Asia R&D April 9, 2007 LO feed through minimization process  Use a 4 MHz baseband tone. Reduce the input level so that the upper side band is more than 60 dB down or into the noise level.  The detector gives a 4 MHz LO feed-through, and a 8 MHz upper side band.  Use a low frequency bandpass filter to detect the LO feed-through  Adjust offset controls till lo feed-through is minimized (2 dimensional search) f 4 MHz LO Feed- through

115 KavoshCom Asia R&D April 9, 2007 The Side-band minimization process f 4 MHz Minimized LO feed- through Undesired sideband Desired sideband Change the input frequency to 2 MHz In crease the input level. The LSB and USB will both increase. The detector detects a 4MHz USB, a 8 MHz USB 3 rd harmonic. The 4 MHz LSB 3 rd harmonic falls on the undesired signal! Adjust  G and  to minimize the USB. The rejection is limited by the 3 rd harmonic levels which is set by the transmit mixer

116 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

117 KavoshCom Asia R&D April 9, 2007 Will this calibration work across the band?  In single carrier systems single frequency interference and even non-flat noise spectrum can be tolerated.  In OFDM systems S/N has to be fixed across the band  Optimum  G and  do not stay the same vs. frequency!  What are the sources of the error vs. frequency?

118 KavoshCom Asia R&D April 9, 2007 Edge of the band matching in filters  In a 1 st order filter 0.5% mismatch in components results in 1.14 degree phase error at the edge of the band.  In a 5 th order filter assuming random component values the expected phase error will be 3.6 degrees at the edge of the band. R I C C+  C R+  R Q I out Q out

119 KavoshCom Asia R&D April 9, 2007 Filter gain response Filter phase response System gain mismatch System phase mismatch OFDM base-band spectrum

120 KavoshCom Asia R&D April 9, 2007 Broadband gain mismatch compensated by  G but residual gain error still at the band edge! Broadband phase mismatch compensated by  control with LLL, but residual phase error still at the band edge!

121 KavoshCom Asia R&D April 9, 2007 The solution is using base-band filter loop back techniques and saving frequency dependent calibration values in the DSP

122 KavoshCom Asia R&D April 9, 2007 What is WiMax Is 3G dead? No way! Basic WiMax RF Specs RF System level analysis Multiband front-end, filter, Tx design Quadrature errors Quadrature calibration Remaining Subcarrier Errors Conclusions Outline

123 KavoshCom Asia R&D April 9, WiMax is the best the telecom technology offers, but 3G is in hot pursuit! The testing methodology to separate the RF and DSP designers is very critical. Direct Conv. with new VCO/synthesizer techniques is the way to go. The Quadrature calibrations issues are the key to success. What did we learn?


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