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Wide-band Receiver Architecture with Flexible Blocker Filtering Techniques

Wide-band Receiver Architecture with Flexible Blocker Filtering Techniques. AUTHORS: Christian IZQUIERDO Franck MONTAUDON Philippe CATHELIN Andreas KAISER. Outline. Introduction BB-RF Feedback Receiver Negative Feedback Architectures Low pass filter configuration

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Wide-band Receiver Architecture with Flexible Blocker Filtering Techniques

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  1. Wide-band Receiver Architecture with Flexible Blocker Filtering Techniques AUTHORS: Christian IZQUIERDO Franck MONTAUDON Philippe CATHELIN Andreas KAISER

  2. Outline • Introduction • BB-RF Feedback Receiver • Negative Feedback Architectures • Low pass filter configuration • High pass filter configuration • Positive Feedback Architecture • Stability Analysis • Noise Figure • Conclusions

  3. Introduction Software Defined Radio Wide-band LNA + Mixer + Configurable BB filter → Multi-standard application * Ref: ISSCC2006 – R. Bagheri, “An 800MHz to 5GHz SDR receiver in 90nm CMOS” SAW GSM External components to obtain good linearity performances (specially in cellular application) → Duplexer + SAW Filter Wide-band LNA SAW WCDMA SAW LTE

  4. Typical Multi-standard RX-TX On-chip • On-chip circuit • Too many SAW filters SAW Filter: Attenuation@40MHz=45dB  Expensive  Big area  2-3dB signal loss  1 Band = 1 SAW Filter Focus on: Relaxing RF filter requirements * Ref: ISSCC2009 – T. Sowlati – Skyworks Solutions

  5. State of the art – On-chip interferer rejection • Translation feed-forward loop receiver • Linearity enhancement scheme with IM3 cancellation Blockers signals Carrier signal * Ref: ISSCC2008 – E. Keehr * Ref: JSSC2007 – H. Darabi Requirement of a very high linearity LNA!!!

  6. BB-RF Feedback Receiver Wide-band Mixer Ampli BB Filter ADC LNA (Gmix) (Gamp) GLNA I/Q Path FLO gOTA Feedback Feedback Feedback Current Mixer (Gmix) Filter (Gfil) I/Q Path Idea: Translate BB filtering to RF input thanks to the feedback • RF Filtering at the LNA input Blocker signals are attenuated

  7. Model of BB-RF Negative Feedback Receiver G: forward voltage gain gR: feedback loop transconductance gain RF Filtering at the LNA input Matching to the antenna impedance in-band. Mismatching out-band RF Central frequency = FLO

  8. LPF fLO fBB fRF fRF Low Pass filter configuration – Theorical Analysis Mixer Ampli (Gmix) (Gamp) Blocker signal fRF Carrier signal LNA + Voie I/Q FLO - gOTA LPF FLO Ampli Feedback V / I Mixer(Gmix) I/Q Path Openloop: ZIN=ZLNA > ZANT Closeloop: ZIN(fLO) = ZANT Input Impedance Mathematical expression

  9. ZIN=50Ω LPF Configuration – Simulation results Input Impedance Input Voltage ZLNA=1KΩ Over voltage • Matching in-band (ZIN=50Ω) and mismatching out-band (ZIN>50Ω) • Over voltage for out-of-band signals in LNA input

  10. HPF fLO fBB fRF High Pass filter configuration – Theorical Analysis Mixer Ampli (Gmix) (Gamp) fRF Blocker signal Carrier signal LNA + Voie I/Q FLO - FLO gOTA HPF Ampli Feedback V / I Mixer(Gmix) I/Q Path fRF Openloop: ZIN=ZLNA > ZANT (Image Frequency) Closeloop: ZIN(fLO) = ZANT Input Impedance Mathematical expression

  11. HPF Configuration – Simulation results Input Impedance Input Voltage ZLNA=1KΩ ZIN=50Ω Att=2.5dB • Matching in-band (ZIN=50Ω) and mismatching out-band (ZIN<50Ω) • Image Frequency of first mixer superposed with BB signal. • Attenuation is not good (<3dB)

  12. LPF fLO fBB fRF fRF fRF Positive Feedback Architecture Mixer Ampli LNA (Gmix) (Gamp) Blocker signal Carrier signal + GLNA + Voie I/Q FLO FLO gOTA LPF Ampli Feedback V / I Mixer(Gmix) I/Q Path Openloop: ZIN=ZLNA < ZANT In-band signal enhanced Input Impedance Mathematical expression:

  13. Results simulation Input Impedance Input Voltage ZLNA=10Ω ZLNA=3Ω Att=19dB • Matching in-band (ZIN=50Ω) and mismatching out-band (ZIN<50Ω) • Good attenuation. It depends of initial ZLNA

  14. Stability Analysis Feed-back Gain: Stability condition For f=fLO: S2=-1.07 S1=-0.88 (-1,0) • Stable for S1 • Unstable for S2

  15. Noise Figure X1 A: forward voltage gain B: feedback loop voltage gain FA: NF of forward path FB: NF of feedback loop + XA XS XO A + B XB X2 Feedback path contribution Forward path contribution

  16. Application Example For ZLNA=3: If A=36dB  gR=4.9mS, B=gR*ZIN(fLO) = 0.245 With these values, S=-0.88>-1 System is stable!!! NFCL to be compared to NF of SAW+ Typical Receiver

  17. Conclusions • BB-RF Positive Feedback Receiver • Channel Filtering in RF • Good blocker rejection (19 dB) • Adjustable BW and center frequency • Attenuation depending on Design Trade-offs: ZLNA, NF and Stability • Though not yet sufficient to remove the SAW filter, this technique • Relaxes filtering requirements • Allows more compact and less expensive receivers

  18. Thank you!!!

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