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

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Presentation on theme: "Special Topics in Electronics Engineering Emad Hegazi Professor, ECE Communication Circuits Research Group Spring 2014."— Presentation transcript:

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

2 17! E s /N o or E b /N o =? Spring 2014 Spring 2014 RF Systems and Circuits

3 Noise Figure Calculation receiver Baseband RF input Spring 2014 Spring 2014 RF Systems and Circuits

4 IP3 Calculation Spring 2014 Spring 2014 RF Systems and Circuits

5 Simplified Transceiver Architecture Spring 2014 Spring 2014 RF Systems and Circuits

6 Role of a Receiver 0 90 A D A D HPMX-2007 The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. Power Supply uP/ DSP Low Noise Amplifier Mixe r Oscillato r 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 Informatio n bias Antenn a Spring 2014 Spring 2014 RF Systems and Circuits

7 Can we use a BPF for channel selection? M. El-Nozahi7 B. Razavi: RF Microelectronics, 2 nd Edition Too large cannot be achieved Spring 2014 Spring 2014 RF Systems and Circuits

8 Band Selection 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-Nozahi8 B. Razavi: RF Microelectronics, 2 nd Edition Desired Band f Band Select filter Spring 2014 Spring 2014 RF Systems and Circuits

9 Band Selection 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-Nozahi9 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

10 Band Selection 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-Nozahi10 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

11 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-Nozahi11 Spring 2014 Spring 2014 RF Systems and Circuits

12 Superheterodyne Receiver Spring 2014 Spring 2014 RF Systems and Circuits

13 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 Spring 2014 Spring 2014 RF Systems and Circuits

14 Typical Superheterodyne Digital Receiver 14 Prof. E Sanchez-Sinencio RF course slides AdvantageDisadvantages Good selectivityHigh complexity Good sensitivityHigh power consumption Image problem External components Not suitable for multi- standard Spring 2014 Spring 2014 RF Systems and Circuits

15 The Image Problem The image could be another user or standard The image must be filtered out before going the mixer Frequency planning is key 15 Prof. E Sanchez-Sinencio RF course slides Spring 2014 Spring 2014 RF Systems and Circuits

16 Image Rejection Calculation SNR min f IF IR required f RF f LO P desired P Image (all in dB ’ s) Spring 2014 Spring 2014 RF Systems and Circuits

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

18 Super-heterodyne Receiver Spring 2014 Spring 2014 RF Systems and Circuits

19 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 Spring 2014 Spring 2014 RF Systems and Circuits

20 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?? Spring 2014 Spring 2014 RF Systems and Circuits

21 Image problem converting to IF A 1 cos( w RF t) A has desired signal at  IF plus an interference at  IM A 2 cos( w IM t) B is at  LO And:  RF -  LO =  LO -  IM =  IF Both converted to IF, Can ’ t be cleaned once corrupted Spring 2014 Spring 2014 RF Systems and Circuits

22 Image Problem Spring 2014 Spring 2014 RF Systems and Circuits

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

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

25 The Image Problem Image Reject filter versus channel selection: Larger IF frequencies requires channel select filter with higher Q M. El-Nozahi25 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

26 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-Nozahi26 Spring 2014 Spring 2014 RF Systems and Circuits

27 Down Conversion to IF M. El-Nozahi27 AM modulation: FM/ Digital..etc. modulations: Spring 2014 Spring 2014 RF Systems and Circuits

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

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

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

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

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

33 Image Reject Receivers-I M. El-Nozahi33 f fcfc -f c Re Im f fcfc -f c Re Im Spring 2014 Spring 2014 RF Systems and Circuits

34 Hilbert transform: A 90 o phase shift results in: –Rotating positive frequency components CW by 90 o –Rotating negative frequency components CCW by 90 o Multiplication by +j rotates all frequency components CCW by 90 o. Multiplication by -j rotates all frequency components CW by 90 o. Note that for DC frequencies these transformations do not have any meaning M. El-Nozahi34 Spring 2014 Spring 2014 RF Systems and Circuits

35 Hilbert transform Assume I(t) is shifted by 90 o to produce Q(t). Find I(t)+jQ(t). M. El-Nozahi35 f fcfc -f c Re{I} Im{I} f fcfc -f c Re{Q} Im{Q} f fcfc -f c Re{jQ} Im{jQ} Im{I+jQ} f fcfc -f c Re{I+jQ} Spring 2014 Spring 2014 RF Systems and Circuits

36 Image Reject Receivers Idea: From the previous example it seems that one could remove the image with the help of quadrature components. M. El-Nozahi36 f fsfs -f s Re{I} Im{I} -f i fifi f Re{I} Im{I}} -f IF f IF f LO f Re{Q} Im{Q} -f IF f IF Spring 2014 Spring 2014 RF Systems and Circuits

37 Hartley Image Reject Architecture A Hilbert transform is used to cancel the image I&Q (quadrature) signals are generated for image rejection. The generation of the 90 o could be achieved using RC phase shifter each providing 45 o phase shift (narrow band solution) M. El-Nozahi37 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

38 Hartley Image Reject Architecture 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-Nozahi38 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

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

40

41

42

43 Spring 2014 Spring 2014 RF Systems and Circuits

44 IRR

45 Input image power ratio

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

47 Weaver Image Reject Architecture Hilbert transform is obtained using another quadrature (complex) mixing stage Advantages compared to Hartley: –Better accuracy in generating the additional 90 o phase shift –IRR is limited to 40 dB, which is higher than Hartley architecture Disadvantages: –Secondary image problem M. El-Nozahi47 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

48 Direct Conversion Receiver A single step down conversion is used. The output frequency is at DC M. El-Nozahi48 B. Razavi: RF Microelectronics, 2 nd Edition AdvantagesDisadvantages No image problemLO leakage Less complex / low power consumption DC offset Channel selection is done with a LPFEven order distortion Effect of mixer spurs are reducedFlicker noise IQ mismatch Spring 2014 Spring 2014 RF Systems and Circuits

49 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) M. El-Nozahi49 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

50 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) M. El-Nozahi50 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

51 Even Order Distortion M. El-Nozahi51 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

52 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 M. El-Nozahi52 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits

53 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 M. El-Nozahi53 Amplitude mismatch: Phase mismatch: Spring 2014 Spring 2014 RF Systems and Circuits

54 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 54 Complex Filter Large Requires matching Power hungry Spring 2014 Spring 2014 RF Systems and Circuits

55 Low IF receiver - 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 + Eliminate IF SAW, IF PLL and image filtering + Integration + Relaxes image rejection requirements + Avoids DC problems, relaxes 1/f noise problem Spring 2014 Spring 2014 RF Systems and Circuits

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

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

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

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

60 Complex Mixing Spring 2014 Spring 2014 RF Systems and Circuits

61 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 61 Spring 2014 Spring 2014 RF Systems and Circuits

62 Direct Conversion Receiver Little image problem No IQ IF Spring 2014 Spring 2014 RF Systems and Circuits

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

64 DC Offset (Self-mixing) A D  c a LO (t)=A LO cos(  c +  ) 0  c capacitive coupling substrate coupling bondwire coupling Saturates the following stages A D  c 0 Spring 2014 Spring 2014 RF Systems and Circuits

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

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

67 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 Spring 2014 Spring 2014 RF Systems and Circuits

68 Even-Order Distortion Direct feed through Interferers y(t) =  1 x(t) +  2 x 2 (t)   2 A 1 A 2 cos(  ) Spring 2014 Spring 2014 RF Systems and Circuits

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

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

71 Mirror Signal Suppression Quadrature Down Conversion A D 0 90 A D a(t) u i (t) u q (t) v i (t) v q (t) I Q Spring 2014 Spring 2014 RF Systems and Circuits

72 Quadrature Conversion Spring 2014 Spring 2014 RF Systems and Circuits

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

74 I/Q Mismatch 0 90 I Q Phase & Gain Error a(t) Spring 2014 Spring 2014 RF Systems and Circuits

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

76 Spring 2014 Spring 2014 RF Systems and Circuits

77 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 Spring 2014 RF Systems and Circuits

78 0 90 a(t) A/D Base Band DSP Phase and gain mismatch compensation DC and 1/f cancellation Spring 2014 Spring 2014 RF Systems and Circuits

79 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 Spring 2014 RF Systems and Circuits

80 Balun Spring 2014 Spring 2014 RF Systems and Circuits Texas Instruments 2006

81 Phase Noise Spring 2014 Spring 2014 RF Systems and Circuits Texas Instruments 2006

82 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. Spring 2014 Spring 2014 RF Systems and Circuits

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

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

85 Transmitter Architectures Direct Conversion Transmitter Two-step Conversion Transmitter Offset PLL Transmitter Spring 2014 Spring 2014 RF Systems and Circuits

86 Direct-conversion transmitter 0 90 I Q  LO Pros: less spurious synthesized Cons: more LO pulling Spring 2014 Spring 2014 RF Systems and Circuits

87 Direct-conversion transmitter with offset LO 0 90 I Q  LO 11 22 Pros: less LO pulling Cons: more spurious synthesized Spring 2014 Spring 2014 RF Systems and Circuits

88 0 90 I Q cos  1 t cos  2 t 1212 Pros: less LO pulling superior IQ matching Cons: required high-Q bandpass filter Two-step transmitter Spring 2014 Spring 2014 RF Systems and Circuits

89 Offset PLL Transmitter 0 90 I Q cos  1 t PD/LPF VCO 1/N Spring 2014 Spring 2014 RF Systems and Circuits

90 Simplified Transceiver Architecture Spring 2014 Spring 2014 RF Systems and Circuits 90

91 Role of a Receiver 0 90 A D A D HPMX-2007 The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw The lkhefw wlkhq wilehr wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. esjlkh qwh wlh lihewrw wklhjr qlih qilh q q3wih q wejklh wajkhrqwilu wae. Power Supply uP/ DSP Low Noise Amplifier Mixe r Oscillato r 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 Informatio n bias Antenn a Spring 2014 Spring 2014 RF Systems and Circuits 91

92 Can we use a BPF for channel selection? B. Razavi: RF Microelectronics, 2 nd Edition Too large cannot be achieved Spring 2014 Spring 2014 RF Systems and Circuits 92

93 Band Selection 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 B. Razavi: RF Microelectronics, 2 nd Edition Desired Band f Band Select filter Spring 2014 Spring 2014 RF Systems and Circuits 93

94 Band Selection 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 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 94

95 Band Selection 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 B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 95

96 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. Spring 2014 Spring 2014 RF Systems and Circuits 96

97 Superheterodyne Receiver Spring 2014 Spring 2014 RF Systems and Circuits 97

98 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 Spring 2014 Spring 2014 RF Systems and Circuits 98

99 Typical Superheterodyne Digital Receiver Prof. E Sanchez-Sinencio RF course slides AdvantageDisadvantages Good selectivityHigh complexity Good sensitivityHigh power consumption Image problem External components Not suitable for multi- standard Spring 2014 Spring 2014 RF Systems and Circuits 99

100 The Image Problem The image could be another user or standard The image must be filtered out before going the mixer Frequency planning is key Prof. E Sanchez-Sinencio RF course slides Spring 2014 Spring 2014 RF Systems and Circuits 100

101 Image Rejection Calculation SNR min f IF IR required f RF f LO P desired P Image (all in dB ’ s) Spring 2014 Spring 2014 RF Systems and Circuits 101

102 Mixer = Multiplying  up/down conversion Frequency translation device Ideal mixer: Doesn’t “mix”; it multiplies A B AB Spring 2014 Spring 2014 RF Systems and Circuits 102

103 Super-heterodyne Receiver Spring 2014 Spring 2014 RF Systems and Circuits 103

104 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 Spring 2014 Spring 2014 RF Systems and Circuits 104

105 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?? Spring 2014 Spring 2014 RF Systems and Circuits 105

106 Image problem converting to IF A 1 cos( w RF t) A has desired signal at  IF plus an interference at  IM A 2 cos( w IM t) B is at  LO And:  RF -  LO =  LO -  IM =  IF Both converted to IF, Can ’ t be cleaned once corrupted Spring 2014 Spring 2014 RF Systems and Circuits 106

107 Image Problem Spring 2014 Spring 2014 RF Systems and Circuits 107

108 Problem of Image Signal Spring 2014 Spring 2014 RF Systems and Circuits 108

109 Problem of Image Signal Solution: Image Rejection Filter Spring 2014 Spring 2014 RF Systems and Circuits 109

110 The Image Problem Image Reject filter versus channel selection: Larger IF frequencies requires channel select filter with higher Q B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 110

111 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? Spring 2014 Spring 2014 RF Systems and Circuits 111

112 Down Conversion to IF AM modulation: FM/ Digital..etc. modulations: Spring 2014 Spring 2014 RF Systems and Circuits 112

113 High Q Alternatives What is really needed is not really a filter. A cancellation scheme to reject noise is good enough Spring 2014 Spring 2014 RF Systems and Circuits Cosine wave 113

114 High Q Alternatives What if we use a sine wave instead Spring 2014 Spring 2014 RF Systems and Circuits 114

115 Complex Signal Representation Niknejad and Shana’a Spring 2014 Spring 2014 RF Systems and Circuits 115

116 Orthognality of I and Q Niknejad and Shana’a Spring 2014 Spring 2014 RF Systems and Circuits 116

117 Orthogonality Spring 2014 Spring 2014 Design of RF Circuits & Systems Spring 2014 Spring 2014 RF Systems and Circuits 117

118 Image Reject Receivers-I f fcfc -f c Re Im f fcfc -f c Re Im Spring 2014 Spring 2014 RF Systems and Circuits 118

119 Hilbert transform: A 90 o phase shift results in: –Rotating positive frequency components CW by 90 o –Rotating negative frequency components CCW by 90 o Multiplication by +j rotates all frequency components CCW by 90 o. Multiplication by -j rotates all frequency components CW by 90 o. Note that for DC frequencies these transformations do not have any meaning Spring 2014 Spring 2014 RF Systems and Circuits 119

120 Hilbert transform Assume I(t) is shifted by 90 o to produce Q(t). Find I(t)+jQ(t). f fcfc -f c Re{I} Im{I} f fcfc -f c Re{Q} Im{Q} f fcfc -f c Re{jQ} Im{jQ} Im{I+jQ} f fcfc -f c Re{I+jQ} Spring 2014 Spring 2014 RF Systems and Circuits 120

121 Image Reject Receivers Idea: From the previous example it seems that one could remove the image with the help of quadrature components. f fsfs -f s Re{I} Im{I} -f i fifi f Re{I} Im{I}} -f IF f IF f LO f Re{Q} Im{Q} -f IF f IF Spring 2014 Spring 2014 RF Systems and Circuits 121

122 Hartley Image Reject Architecture A Hilbert transform is used to cancel the image I&Q (quadrature) signals are generated for image rejection. The generation of the 90 o could be achieved using RC phase shifter each providing 45 o phase shift (narrow band solution) B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 122

123 Hartley Image Reject Architecture 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. B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 123

124 Implementing the Phase Shift Hartley Architecture with simple 90 deg phase shiftor Spring 2014 Spring 2014 RF Systems and Circuits 124

125 Weaver 125

126 126

127 127

128 Spring 2014 Spring 2014 RF Systems and Circuits 128

129 IRR 129

130 Input image power ratio 130

131 Gain Mismatch due to R, C errors At w = 1/RC: Spring 2014 Spring 2014 RF Systems and Circuits 131

132 Weaver or Hartley? Hilbert transform is obtained using another quadrature (complex) mixing stage Advantages compared to Hartley: –Better accuracy in generating the additional 90 o phase shift –IRR is limited to 40 dB, which is higher than Hartley architecture Disadvantages: –Secondary image problem B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 132

133 Direct Conversion Receiver A single step down conversion is used. The output frequency is at DC B. Razavi: RF Microelectronics, 2 nd Edition AdvantagesDisadvantages No image problemLO leakage Less complex / low power consumption DC offset Channel selection is done with a LPFEven order distortion Effect of mixer spurs are reducedFlicker noise IQ mismatch Spring 2014 Spring 2014 RF Systems and Circuits 133

134 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, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 134

135 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, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 135

136 Even Order Distortion B. Razavi: RF Microelectronics, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 136

137 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, 2 nd Edition Spring 2014 Spring 2014 RF Systems and Circuits 137

138 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: Spring 2014 Spring 2014 RF Systems and Circuits 138

139 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 Spring 2014 Spring 2014 RF Systems and Circuits 139

140 Low IF receiver - 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 + Eliminate IF SAW, IF PLL and image filtering + Integration + Relaxes image rejection requirements + Avoids DC problems, relaxes 1/f noise problem Spring 2014 Spring 2014 RF Systems and Circuits 140

141 Low-IF Down Conversion Complex BPF Mirror signal, needs removal Spring 2014 Spring 2014 RF Systems and Circuits 141

142 Mirror Signal Suppression Complex Bandpass Filter I Q I Q LO1 LO2 Spring 2014 Spring 2014 RF Systems and Circuits 142

143 Complex Mixing- Real LO Spring 2014 Spring 2014 RF Systems and Circuits 143

144 Complex Mixing-Complex LO Spring 2014 Spring 2014 RF Systems and Circuits 144

145 Complex Mixing Spring 2014 Spring 2014 RF Systems and Circuits 145

146 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 Spring 2014 RF Systems and Circuits 146

147 Direct Conversion Receiver Little image problem No IQ IF Spring 2014 Spring 2014 RF Systems and Circuits 147

148 Direct Conversion Receiver LO is at same frequency as RF 1/f noise here can end up in channel Self mixing cause DC problem + Eliminate IF SAW, IF PLL and image filtering + Integration + easier image problem - Quadrature RF down conversion required - DC problem - Typically requires offset or 2x LO to avoid coupling Spring 2014 Spring 2014 RF Systems and Circuits 148

149 DC Offset (Self-mixing) A D  c a LO (t)=A LO cos(  c +  ) 0  c capacitive coupling substrate coupling bondwire coupling Saturates the following stages A D  c 0 Spring 2014 Spring 2014 RF Systems and Circuits 149

150 DC Offset (Self-mixing) level DC Offset + - t Spring 2014 Spring 2014 RF Systems and Circuits 150

151 DC Offset Cancellation Capacitive Coupling –Requires a large capacitor Negative Feedback –Nonlinear -A Spring 2014 Spring 2014 RF Systems and Circuits 151

152 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 Spring 2014 Spring 2014 RF Systems and Circuits 152

153 Even-Order Distortion Direct feed through Interferers y(t) =  1 x(t) +  2 x 2 (t)   2 A 1 A 2 cos(  ) Spring 2014 Spring 2014 RF Systems and Circuits 153

154 Mirror Signal Upper sideband and lower sideband are identical Spring 2014 Spring 2014 RF Systems and Circuits 154

155 Mirror Signal Upper sideband and lower sideband are not identical Spring 2014 Spring 2014 RF Systems and Circuits 155

156 Mirror Signal Suppression Quadrature Down Conversion A D 0 90 A D a(t) u i (t) u q (t) v i (t) v q (t) I Q Spring 2014 Spring 2014 RF Systems and Circuits 156

157 Quadrature Conversion Spring 2014 Spring 2014 RF Systems and Circuits 157

158 Quadrature Down Conversion Spring 2014 Spring 2014 RF Systems and Circuits 158

159 I/Q Mismatch 0 90 I Q Phase & Gain Error a(t) Spring 2014 Spring 2014 RF Systems and Circuits 159

160 I/Q Mismatch due to LO errors Spring 2014 Spring 2014 RF Systems and Circuits 160

161 Spring 2014 Spring 2014 RF Systems and Circuits 161

162 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 Spring 2014 RF Systems and Circuits 162

163 0 90 a(t) A/D Base Band DSP Phase and gain mismatch compensation DC and 1/f cancellation Spring 2014 Spring 2014 RF Systems and Circuits 163

164 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 Spring 2014 RF Systems and Circuits 164

165 Outline Friis Formula Merits of LNAs Common Gate LNA Common Source LNA Highly Linear LNA Wideband LNAs Mixers Spring 2014 Spring 2014 RF Systems and Circuits

166 Cascaded Noise Figure In a line-up of receiver stages, use Friis equation G i is the power gain Says that the noise factor ‘F’ is more influenced by earlier stages Spring 2014 Spring 2014 RF Systems and Circuits

167 LNA Merits Gain Low Noise (NF) High Linearity (IIP3) Low Reflection (S11) High reverse isolation (S12) High Stability (K) Spring 2014 Spring 2014 RF Systems and Circuits

168 Common Gate LNA Input impedance is resistive (except for parasitics) Offers good impedance match even at low frequencies Spring 2014 Spring 2014 RF Systems and Circuits

169 Common Gate LNA tunes out transistor and board parasitics. Channel resistance offers good reverse isolation Spring 2014 Spring 2014 RF Systems and Circuits

170 Common Gate LNA At matching condition, Zin = 1/gm Spring 2014 Spring 2014 RF Systems and Circuits

171 Common Gate LNA: Lowering Power II Narrowband impedance transformer (L Section) allows the LNA to have Zin>50 . Transformer amplifies input signal by: Spring 2014 Spring 2014 RF Systems and Circuits

172 Common Gate LNA: Lowering Power II For same IIP3, V eff has to increase by Current is reduced by the same factor Bias current is given by: Spring 2014 Spring 2014 RF Systems and Circuits

173 Common Source Amplifier Input impedance is purely capacitive Resistive part appears at high frequency No input matching is possible Spring 2014 Spring 2014 RF Systems and Circuits

174 Common Source Amplifier Rg is set to 50  => Input Matching Miller Effect due to C gd => Limited Bandwidth Spring 2014 Spring 2014 RF Systems and Circuits

175 Common Source Amplifier Cascode reduces Miller Effect Resistive Load limits linearity Spring 2014 Spring 2014 RF Systems and Circuits

176 Common Source Amplifier Parallel Resonance at output boasts narrow band gain without impacting linearity R g produces a lot of Noise NF>3 dB Spring 2014 Spring 2014 RF Systems and Circuits

177 Common Source Amplifier Series resonance at input creates a resistive term I in = j  C gs V gs V in =V gs +j  L s (I in +g m V gs ) g m V gs I in Spring 2014 Spring 2014 RF Systems and Circuits

178 Common Source Amplifier Series resonance at input creates a resistive RF, input is still capacitive because L s is very small to give 50  with high  T Spring 2014 Spring 2014 RF Systems and Circuits

179 Common Source Amplifier Gate inductance offers one more degree of freedom to allow matching and series resonance at the same time Valid for Spring 2014 Spring 2014 RF Systems and Circuits

180 Parasitics Ali Niknejad ECE142 Spring 2014 Spring 2014 RF Systems and Circuits

181 Design Procedure for Common Source LNAs Spring 2014 Spring 2014 RF Systems and Circuits

182 Common Source Amplifier Assume an equivalent resistive load R resonance Spring 2014 Spring 2014 RF Systems and Circuits

183 Common Source Amplifier Noise Figure (F) is given by Decreases with  T Use samll L s Source CoilsTransistor Spring 2014 Spring 2014 RF Systems and Circuits

184 Optimization of CS LNA Input matching condition Spring 2014 Spring 2014 RF Systems and Circuits

185 Optimization of CS LNA  T Increases L g Noise dominates Higher power Spring 2014 Spring 2014 RF Systems and Circuits

186 Another Way to Look at It If Q is input quality factor Spring 2014 Spring 2014 RF Systems and Circuits

187 Another Way to Look at It The input is amplified by Q before it reaches the transistor This reduces linearity Spring 2014 Spring 2014 RF Systems and Circuits

188 Other Losses: Inductor Losses Typically L g losses dominate Adds in series to source noise Independent of FET gain Spring 2014 Spring 2014 RF Systems and Circuits

189 Other Losses: Gate Resistance Gate Resistance creates additional noise (uncorrelated with channel noise) Use inter-digitated layout to reduce gate electrode resistance Spring 2014 Spring 2014 RF Systems and Circuits

190 Other Losses: Gate Induced Noise Due to inversion layer resistance Partly correlated with conventional thermal noise Modeled as a resistance in series with gate Spring 2014 Spring 2014 RF Systems and Circuits

191 Other Losses: Gate Induced Noise The effective Q is lowered by losses Higher Q is achieved through lower C gs Smaller C gs raises rinv and also gate resistance There is an optimum W at each current Spring 2014 Spring 2014 RF Systems and Circuits

192 Other Losses: Substrate Coupling BSIM3V3 models do NOT capture Cgb Gate to bulk capacitance is an additional path for noise Spring 2014 Spring 2014 RF Systems and Circuits

193 Other Losses: Substrate Coupling Hole distribution in the depletion layer are modulated by gate voltage Same effect on electrons in the inversion layer which reflects back on depletion region Spring 2014 Spring 2014 RF Systems and Circuits

194 Wideband CS LNA Uses an LC ladder filter to widen BW Uses a large number of inductors Excellent noise performance Spring 2014 Spring 2014 RF Systems and Circuits

195 Resistive Feedback Feedback widens BW and lowers Z in Power consumption is very high Noise Cancellation can be employed Spring 2014 Spring 2014 RF Systems and Circuits

196 Capacitive Cross Coupling Technique Differential input impedance: Two voltage noise sources: v ns & v n1 in each half circuit Spring 2014 Spring 2014 RF Systems and Circuits

197 The output differential noise current square due to each noise source is given by: Then: Using the input power matching condition: Capacitive Cross-Coupling Technique Spring 2014 Spring 2014 RF Systems and Circuits


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