1. 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

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 2 2 2 2 2

3. 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

4. Typical Multi-standard RX-TX
On-chip
On-chip circuit
Too many SAW filters
SAW Filter: 
 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

5. 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

6. 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

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. 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

9. 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

10. 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

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)
titre

12. 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

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

15. A B Noise Figure A: forward voltage gain B: feedback loop voltage gainXS 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

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!!!
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

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 17 17 17 17 17

18. Thank you!!!