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

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 2 2 2 2 2

Introduction Software Defined Radio → Multi-standard application 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 Wide-band LNA SAW LTE SAW WCDMA External components to obtain good linearity performances (specially in cellular application) → Duplexer + SAW Filter Replace figure

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 Souligner le recepteur en etude * Ref: ISSCC2009 – T. Sowlati – Skyworks Solutions

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

BB-RF Feedback Receiver I/Q Path Wide-band Mixer Ampli BB Filter ADC LNA (Gmix) (Gamp) GLNA 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

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

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

LPF Configuration – Simulation results Input Impedance Input Voltage ZIN=50Ω 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

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

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) titre

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

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

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

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

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!!! NFA B NFB NFCL 3.4 0.245 4.7 3.52 6.9 3.75 10.4 4.36 13.2 5.23 NFCL to be compared to NF of SAW+ Typical Receiver

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 17 17 17 17 17

Thank you!!!