Special Topics in Electronics Engineering

Special Topics in Electronics Engineering
Spring 2014 RF Systems and Circuits Special Topics in Electronics Engineering Emad Hegazi Professor, ECE Communication Circuits Research Group

Spring 2014 RF Systems and Circuits Es/No or Eb/No=? 17!

Noise Figure Calculation
Spring 2014 RF Systems and Circuits Noise Figure Calculation RF input Baseband receiver 利用先前的公式可以計算出接收器的Noise Figure需要多小才能符合系統規格。

IP3 Calculation RF Systems and Circuits
Spring 2014 RF Systems and Circuits IP3 Calculation 利用系統規格的動態範圍以及所需的SNR可以計算出接收器的IP3規格。

Simplified Transceiver Architecture
Spring 2014 RF Systems and Circuits Simplified Transceiver Architecture In Hartley architecture, it translates the RF signal to IF signal by the different phase of the local oscillator, sinwt and coswt. Finally, the i-phase and the q-phase signal with 90 degree phase shifter are combined at the output. Thus the image signal has been suppressed.

Role of a Receiver RF Systems and Circuits Power Supply
Spring 2014 RF Systems and Circuits Role of a Receiver 90 A D HPMX-2007 The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q Power Supply uP/ DSP Low Noise Amplifier Mixer Oscillator Baseband Processor De-Modulator bias I Data Q Data 1. amplify received signal with min. added noise 2. shift to lower frequency (cost and/or performance) 3. LO for down conversion 4. discard carrier and recover data Information Antenna

Can we use a BPF for channel selection?
Spring 2014 RF Systems and Circuits Can we use a BPF for channel selection? The adjacent channels are always considered as interferers. These interferes could affect the reception of the signal. It is important to filter the unnecessary channels Example: It is desired to filter the alternate channel by 35 dB using an LC-BPF. Determine the quality factor of the tank. Solution: 𝑍 𝑠 = 𝑅𝐿𝑠 𝑅𝐿𝐶 𝑠 2 +𝐿𝑠+𝑅 𝑍 𝑠 𝑅 ≈ 1 1+2𝑗𝑄 ∆𝑓 𝑓 𝑜 𝑄=63,200 B. Razavi: RF Microelectronics, 2nd Edition Too large cannot be achieved M. El-Nozahi

Band Selection The BPF before the LNA is used as a band select filter
Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition Band Select filter f Desired Band The BPF before the LNA is used as a band select filter Specification is relaxed compared to the case where it is used as a channel select filter It has a constant frequency response and does not need to be tunable The BPF is implemented using: SAW technology for frequencies below 10 GHZ MEMS technology for mm-wave frequencies M. El-Nozahi

Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition TX-RX feedthrough can limit the performance of the receiver Typically the received signal is in the order of -70 dBm Feedthrough may saturate the BB blocks because of the high gain Is an issue in full duplex transceivers Design Targets: LNA must tolerate this high input level A BPF is usually included at the output of LNA provide additional filtering M. El-Nozahi

Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition Band select filters are usually implemented in a duplexer Single antenna transceivers use a duplexer to isolate between TX and RX Duplexers are two BPF, one for RX and the other for TX M. El-Nozahi

Channel Selection Remarks
Spring 2014 RF Systems and Circuits Channel Selection Remarks Channel selection cannot be done before the LNA because: It is hard to find a BPF with large quality factor, and achieving a very small loss Having a tunable BPF with high quality factor is hard to obtained Usually, there are two steps to select a channel: Band selection: In which the entire band is selected. This step usually comes before the LNA. Channel selection: In which the desired channel is selected. This step is usually done after the first mixer. M. El-Nozahi

Superheterodyne Receiver
Spring 2014 RF Systems and Circuits Superheterodyne Receiver

Example: AM Radio AM radio band: 530 to 1610 KHz
Spring 2014 RF Systems and Circuits Example: AM Radio AM radio band: 530 to 1610 KHz BW/2 = ( )/2=1080/2=540, in band IF has to be lower. Commonly: 455kHz Image can be in AM band If LO is on low side, LO tuning range is: (530 to 1610) – 455 = (75 to 1155) LO lowest to highest is a factor of 15.4 If LO is on high side, LO tuning range is: (530 to 1610) = (985 to 2065) LO lowest to highest is a factor of 2.01

Typical Superheterodyne Digital Receiver
Spring 2014 RF Systems and Circuits Typical Superheterodyne Digital Receiver Prof. E Sanchez-Sinencio RF course slides Advantage Disadvantages Good selectivity High complexity Good sensitivity High power consumption Image problem External components Not suitable for multi-standard

The Image Problem The image could be another user or standard
Spring 2014 RF Systems and Circuits The Image Problem Prof. E Sanchez-Sinencio RF course slides The image could be another user or standard The image must be filtered out before going the mixer Frequency planning is key

Image Rejection Calculation
Spring 2014 RF Systems and Circuits Image Rejection Calculation PImage IRrequired Pdesired SNRmin 決定了中頻之後，依據系統的規格可以計算出鏡像消除的規格。 fIF fRF fLO (all in dB’s)

Mixer = Multiplying  up/down conversion
Spring 2014 RF Systems and Circuits Mixer = Multiplying  up/down conversion Frequency translation device Ideal mixer: Doesn’t “mix”; it multiplies AB A B

Super-heterodyne Receiver
Spring 2014 RF Systems and Circuits Super-heterodyne Receiver In Hartley architecture, it translates the RF signal to IF signal by the different phase of the local oscillator, sinwt and coswt. Finally, the i-phase and the q-phase signal with 90 degree phase shifter are combined at the output. Thus the image signal has been suppressed.

Selection of IF If IF is large, Other IF selection criteria
Spring 2014 RF Systems and Circuits Selection of IF If IF is large, better separation between RF and image better image rejection easier image rejection filter design More stages of down conversion Other IF selection criteria Select IF so that image freq is outside of RF band IF >= (RF BW)/2 Sometime may not be possible, if (RF BW)/2 is within RF Band

Q: should LO > RF, or LO < RF??
Spring 2014 RF Systems and Circuits For each channel assignment, there are two choices of LO freq that meets the requirement |RF–LO|=IF. Q: should LO > RF, or LO < RF??

Image problem converting to IF
Spring 2014 RF Systems and Circuits Image problem converting to IF A has desired signal at wIF A1cos(wRFt) plus an interference at wIM A2cos(wIMt) B is at wLO And: In Hartley architecture, it translates the RF signal to IF signal by the different phase of the local oscillator, sinwt and coswt. Finally, the i-phase and the q-phase signal with 90 degree phase shifter are combined at the output. Thus the image signal has been suppressed. wRF - wLO = wLO - wIM = wIF Both converted to IF, Can’t be cleaned once corrupted

Spring 2014 RF Systems and Circuits Image Problem

Problem of Image Signal
Spring 2014 RF Systems and Circuits Problem of Image Signal

Spring 2014 RF Systems and Circuits Problem of Image Signal Solution: Image Rejection Filter

The Image Problem Image Reject filter versus channel selection:
Spring 2014 RF Systems and Circuits The Image Problem Image Reject filter versus channel selection: Larger IF frequencies requires channel select filter with higher Q B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Dual-IF Heterodyne Receiver
Spring 2014 RF Systems and Circuits Dual-IF Heterodyne Receiver Channel selection is done in two stages, hence relaxing the specification for each stage Secondary image problem To avoid the problem, the second IF frequency is set to zero Is it possible to have a zero IF? M. El-Nozahi

Down Conversion to IF AM modulation: RF Systems and Circuits
Spring 2014 RF Systems and Circuits Down Conversion to IF AM modulation: FM/ Digital ..etc . modulations: M. El-Nozahi

High Q Alternatives What is really needed is not really a filter.
Spring 2014 RF Systems and Circuits High Q Alternatives What is really needed is not really a filter. A cancellation scheme to reject noise is good enough Cosine wave

High Q Alternatives What if we use a sine wave instead
Spring 2014 RF Systems and Circuits High Q Alternatives What if we use a sine wave instead j j -j -j

Complex Signal Representation
Spring 2014 RF Systems and Circuits Complex Signal Representation Niknejad and Shana’a

Orthogonality of I and Q
Spring 2014 RF Systems and Circuits Orthogonality of I and Q Niknejad and Shana’a

Orthogonality Design of RF Circuits & Systems RF Systems and Circuits
Spring 2014 RF Systems and Circuits Orthogonality Spring 2014 Design of RF Circuits & Systems

Image Reject Receivers-I
Spring 2014 RF Systems and Circuits Image Reject Receivers-I What is a shift by 90o? 𝐴 cos 𝜔 𝑐 𝑡−90 =−𝑗 𝐴 2 𝑒 𝑗 𝜔 𝑐 𝑡 +𝑗 𝐴 2 𝑒 −𝑗 𝜔 𝑐 𝑡 The 90o phase shift is also called Hilbert transform Im Im 𝑗 𝐴 2 Re Re 𝐴 2 𝐴 2 fc f -fc fc f -fc −𝑗 𝐴 2 𝑋90(𝜔)=𝑋(𝜔) −𝑗 𝑠𝑔𝑛(𝜔) M. El-Nozahi

Hilbert transform: A 90o phase shift results in:
Spring 2014 RF Systems and Circuits Hilbert transform: A 90o phase shift results in: Rotating positive frequency components CW by 90o Rotating negative frequency components CCW by 90o Multiplication by +j rotates all frequency components CCW by 90o. Multiplication by -j rotates all frequency components CW by 90o. Note that for DC frequencies these transformations do not have any meaning M. El-Nozahi

Spring 2014 RF Systems and Circuits Hilbert transform Assume I(t) is shifted by 90o to produce Q(t). Find I(t)+jQ(t). f fc -fc Re{I} Im{I} f fc -fc Re{Q} Im{Q} f fc -fc Re{jQ} Im{jQ} Im{I+jQ} f fc -fc Re{I+jQ} M. El-Nozahi

Image Reject Receivers
Spring 2014 RF Systems and Circuits Image Reject Receivers Idea: From the previous example it seems that one could remove the image with the help of quadrature components. Im{I}} Re{I} Im{I} Re{I} f -fIF fIF Im{Q} Re{Q} f -fs -fi fi fs fLO f -fIF fIF M. El-Nozahi

Hartley Image Reject Architecture
Spring 2014 RF Systems and Circuits Hartley Image Reject Architecture B. Razavi: RF Microelectronics, 2nd Edition A Hilbert transform is used to cancel the image I&Q (quadrature) signals are generated for image rejection. The generation of the 90o could be achieved using RC phase shifter each providing 45o phase shift (narrow band solution) M. El-Nozahi

Spring 2014 RF Systems and Circuits Hartley Image Reject Architecture B. Razavi: RF Microelectronics, 2nd Edition Still in the BB we must generate another I&Q for digital demodulation Drawbacks: Mismatch between the two path will result in finite image rejection The RC solution can be used for narrow-band architectures. Wideband architecture will result in degraded performance for the image rejection (IRR) Typical values for IRR is lower than 35 dB. M. El-Nozahi

Implementing the Phase Shift
Spring 2014 RF Systems and Circuits Implementing the Phase Shift Hartley Architecture with simple 90 deg phase shiftor

RF Systems and Circuits
Spring 2014 RF Systems and Circuits

Input image power ratio

Gain Mismatch due to R, C errors
Spring 2014 RF Systems and Circuits Gain Mismatch due to R, C errors At w = 1/RC:

Weaver Image Reject Architecture
Spring 2014 RF Systems and Circuits Weaver Image Reject Architecture Hilbert transform is obtained using another quadrature (complex) mixing stage Advantages compared to Hartley: Better accuracy in generating the additional 90o phase shift IRR is limited to 40 dB, which is higher than Hartley architecture Disadvantages: Secondary image problem B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Direct Conversion Receiver
Spring 2014 RF Systems and Circuits Direct Conversion Receiver A single step down conversion is used. The output frequency is at DC B. Razavi: RF Microelectronics, 2nd Edition Advantages Disadvantages No image problem LO leakage Less complex / low power consumption DC offset Channel selection is done with a LPF Even order distortion Effect of mixer spurs are reduced Flicker noise IQ mismatch M. El-Nozahi

Spring 2014 RF Systems and Circuits LO Leakage The LO signal can be leaked to the antenna by the capacitive coupling or substrate For singled ended Los, the LO leakage can reach -60 dBm Differential LO architectures have lower LO leakage (better than dBm) B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Spring 2014 RF Systems and Circuits Direct Conversion Receiver DC Offset: The leaked LO signal can go through the antenna, LNA and down converted Because of the LO signal and its feedthrough signal carry the same frequency, a DC offset is produced (this phenomena is called LO self mixing). BB blocks usually have high again, hence the LO self mixing may saturate the receiver HPF are not common because they require a very low cut-off frequency (large components, slow settling) B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Even Order Distortion RF Systems and Circuits
Spring 2014 RF Systems and Circuits Even Order Distortion B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Spring 2014 RF Systems and Circuits Direct Conversion Receiver Flicker Noise: For g the channel bandwidth is 10MHz. With a noise corner frequency of 200kHz For GSM, the channel bandwidth is 100 kHz and therefore a large portion of noise appears due to flicker noise B. Razavi: RF Microelectronics, 2nd Edition M. El-Nozahi

Spring 2014 RF Systems and Circuits Direct Conversion Receiver IQ mismatch: mismatch in I and Q path affects SNR of received signals Mismatch effects are more dominate at high frequencies. Reducing the frequency at which the I and Q signal are generated enhances the SNR Digital calibration is used to correct these mismatches Amplitude mismatch: Phase mismatch: M. El-Nozahi

Low-IF Receiver Has all the advantages of direct conversion receivers
Spring 2014 RF Systems and Circuits Low-IF Receiver Has all the advantages of direct conversion receivers More difficult image rejection requirements Minimum IF frequency is channel bandwidth DC offset is outside the signal bandwidth Complex Filter Large Requires matching Power hungry

Low IF receiver - Quadrature RF down conversion required
Spring 2014 RF Systems and Circuits Low IF receiver + Eliminate IF SAW, IF PLL and image filtering + Integration + Relaxes image rejection requirements + Avoids DC problems, relaxes 1/f noise problem - Quadrature RF down conversion required - Require higher performance ADC Additional mixer Slower RF PLL settling Even order distortion still problem Low freq IF filters require large chip area

Low-IF Down Conversion
Spring 2014 RF Systems and Circuits Low-IF Down Conversion Complex BPF Mirror signal, needs removal

Mirror Signal Suppression
Spring 2014 RF Systems and Circuits Mirror Signal Suppression Complex Bandpass Filter I Q I Q LO1 LO2

Complex Mixing- Real LO
Spring 2014 RF Systems and Circuits Complex Mixing- Real LO

Complex Mixing-Complex LO
Spring 2014 RF Systems and Circuits Complex Mixing-Complex LO

Spring 2014 RF Systems and Circuits Complex Mixing

Spring 2014 RF Systems and Circuits Bluetooth Receiver Has all the advantages of direct conversion receivers More difficult image rejection requirements Minimum IF frequency is channel bandwidth DC offset is outside the signal bandwidth

Spring 2014 RF Systems and Circuits Direct Conversion Receiver In Hartley architecture, it translates the RF signal to IF signal by the different phase of the local oscillator, sinwt and coswt. Finally, the i-phase and the q-phase signal with 90 degree phase shifter are combined at the output. Thus the image signal has been suppressed. Little image problem No IQ IF

Spring 2014 RF Systems and Circuits Direct Conversion Receiver LO is at same frequency as RF 1/f noise here can end up in channel Self mixing cause DC problem - Quadrature RF down conversion required - DC problem - Typically requires offset or 2x LO to avoid coupling + Eliminate IF SAW, IF PLL and image filtering + Integration + easier image problem

DC Offset (Self-mixing)
Spring 2014 RF Systems and Circuits DC Offset (Self-mixing) A D w c aLO(t)=ALOcos(w c+q) capacitive coupling substrate coupling bondwire coupling Saturates the following stages A D w c

Spring 2014 RF Systems and Circuits DC Offset (Self-mixing) level DC Offset + - t

DC Offset Cancellation
Spring 2014 RF Systems and Circuits DC Offset Cancellation Capacitive Coupling Requires a large capacitor Negative Feedback Nonlinear -A

Spring 2014 RF Systems and Circuits 1/f noise effect CMOS transistors has significant 1/f noise at low to DC frequency Significantly noise performance of direct conversion receivers Receive signal 1/f noise f

Even-Order Distortion
Spring 2014 RF Systems and Circuits Even-Order Distortion Interferers Dw y(t) = a1 x(t) + a2 x2(t) a2 A1A2 cos(Dw) Direct feed through Dw Direct feed through

Mirror Signal Upper sideband and lower sideband are identical
Spring 2014 RF Systems and Circuits Mirror Signal Upper sideband and lower sideband are identical

Mirror Signal Upper sideband and lower sideband are not identical
Spring 2014 RF Systems and Circuits Mirror Signal Upper sideband and lower sideband are not identical

Spring 2014 RF Systems and Circuits Mirror Signal Suppression Quadrature Down Conversion A D 90 a(t) ui(t) uq(t) vi(t) vq(t) I Q

Quadrature Conversion
Spring 2014 RF Systems and Circuits Quadrature Conversion

Quadrature Down Conversion
Spring 2014 RF Systems and Circuits Quadrature Down Conversion

I/Q Mismatch RF Systems and Circuits I Phase & Gain Error a(t) Q 90
Spring 2014 RF Systems and Circuits I/Q Mismatch 90 I Q Phase & Gain Error a(t)

I/Q Mismatch due to LO errors
Spring 2014 RF Systems and Circuits I/Q Mismatch due to LO errors

Spring 2014 RF Systems and Circuits Use of I/Q down conversion recovers the nonsymmetrical receive signal spectrum But port isolation becomes more challenging Selfmixing and even order distortion may affect both channels and affect each other, causing additional I/Q mismatch

Spring 2014 RF Systems and Circuits 90 a(t) A/D Base Band DSP Phase and gain mismatch compensation DC and 1/f cancellation

Summary of Direct Conversion Receiver
Spring 2014 RF Systems and Circuits Summary of Direct Conversion Receiver No need for imager reject filter Suitable for monolithic integration with baseband DC offsets due to crosstalk of input ports of mixer Even order IM direct feed through to baseband Quadrature down conversion suppresses mirror I/Q mismatch due to mismatches in parasitics Low power consumption attributes to less hardware

Spring 2014 RF Systems and Circuits Balun Texas Instruments 2006

Spring 2014 RF Systems and Circuits Phase Noise Texas Instruments 2006

Trsnmitter Paradigms Signal is strong.
Spring 2014 RF Systems and Circuits Trsnmitter Paradigms Signal is strong. We need to make sure efficient delivery of power to the antenna. Spectral content should be contained to its specified limits. Linearity matters if modulation is linear. 傳送器的結構有直接升頻與二次升頻結構。

Transmit Specifications
Spring 2014 RF Systems and Circuits Transmit Specifications Transmit spectrum mask

Transmitter Specifications
Spring 2014 RF Systems and Circuits Transmitter Specifications alternate adjacent channel Adjacent channel 20 20 40 40

Transmitter Architectures
Spring 2014 RF Systems and Circuits Transmitter Architectures Direct Conversion Transmitter Two-step Conversion Transmitter Offset PLL Transmitter 傳送器的結構有直接升頻與二次升頻結構。

Direct-conversion transmitter
Spring 2014 RF Systems and Circuits Direct-conversion transmitter I 90 Q 直接升頻的缺點是LO的信號會透過天線發射出去。 wLO Pros: less spurious synthesized Cons: more LO pulling

Direct-conversion transmitter with offset LO
Spring 2014 RF Systems and Circuits Direct-conversion transmitter with offset LO I wLO 90 w1 Q w2 Pros: less LO pulling Cons: more spurious synthesized

Two-step transmitter RF Systems and Circuits I w1+w2 cosw1t cosw2t Q
Spring 2014 RF Systems and Circuits Two-step transmitter I 90 w1+w2 cosw1t cosw2t Q 二次升頻則先升至中頻，再往上升頻至所要的頻率，是較常見的結構。 Pros: less LO pulling superior IQ matching Cons: required high-Q bandpass filter

Offset PLL Transmitter
Spring 2014 RF Systems and Circuits Offset PLL Transmitter I PD/LPF VCO 90 cosw1t Q 1/N

Simplified Transceiver Architecture
Spring 2014 RF Systems and Circuits Simplified Transceiver Architecture In Hartley architecture, it translates the RF signal to IF signal by the different phase of the local oscillator, sinwt and coswt. Finally, the i-phase and the q-phase signal with 90 degree phase shifter are combined at the output. Thus the image signal has been suppressed.

Role of a Receiver RF Systems and Circuits Power Supply
Spring 2014 RF Systems and Circuits Role of a Receiver 90 A D HPMX-2007 The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q Power Supply uP/ DSP Low Noise Amplifier Mixer Oscillator Baseband Processor De-Modulator bias I Data Q Data 1. amplify received signal with min. added noise 2. shift to lower frequency (cost and/or performance) 3. LO for down conversion 4. discard carrier and recover data Information Antenna

Can we use a BPF for channel selection?
Spring 2014 RF Systems and Circuits Can we use a BPF for channel selection? The adjacent channels are always considered as interferers. These interferes could affect the reception of the signal. It is important to filter the unnecessary channels Example: It is desired to filter the alternate channel by 35 dB using an LC-BPF. Determine the quality factor of the tank. Solution: 𝑍 𝑠 = 𝑅𝐿𝑠 𝑅𝐿𝐶 𝑠 2 +𝐿𝑠+𝑅 𝑍 𝑠 𝑅 ≈ 1 1+2𝑗𝑄 ∆𝑓 𝑓 𝑜 𝑄=63,200 B. Razavi: RF Microelectronics, 2nd Edition Too large cannot be achieved

Band Selection The BPF before the LNA is used as a band select filter
Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition Band Select filter f Desired Band The BPF before the LNA is used as a band select filter Specification is relaxed compared to the case where it is used as a channel select filter It has a constant frequency response and does not need to be tunable The BPF is implemented using: SAW technology for frequencies below 10 GHZ MEMS technology for mm-wave frequencies

Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition TX-RX feedthrough can limit the performance of the receiver Typically the received signal is in the order of -70 dBm Feedthrough may saturate the BB blocks because of the high gain Is an issue in full duplex transceivers Design Targets: LNA must tolerate this high input level A BPF is usually included at the output of LNA provide additional filtering

Spring 2014 RF Systems and Circuits Band Selection B. Razavi: RF Microelectronics, 2nd Edition Band select filters are usually implemented in a duplexer Single antenna transceivers use a duplexer to isolate between TX and RX Duplexers are two BPF, one for RX and the other for TX

Channel Selection Remarks
Spring 2014 RF Systems and Circuits Channel Selection Remarks Channel selection cannot be done before the LNA because: It is hard to find a BPF with large quality factor, and achieving a very small loss Having a tunable BPF with high quality factor is hard to obtained Usually, there are two steps to select a channel: Band selection: In which the entire band is selected. This step usually comes before the LNA. Channel selection: In which the desired channel is selected. This step is usually done after the first mixer.