Wide-band Receiver Architecture with Flexible Blocker Filtering Techniques

AUTHORS: Christian IZQUIERDOFranck MONTAUDONPhilippe CATHELINAndreas KAISER

15/12/102

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

15/12/103

Software Defined RadioWide-band LNA + Mixer + Configurable BB filter

→ Multi-standard application

External components to obtain good linearity performances (specially in cellular application) → Duplexer + SAW Filter

Introduction

* Ref: ISSCC2006 – R. Bagheri, “An 800MHz to 5GHz SDR receiver in 90nm CMOS”

SAW GSM

Wide-band LNA

SAW LTE

SAW WCDMA

15/12/104

• On-chip circuit• Too many SAW filters

* Ref: ISSCC2009 – T. Sowlati – Skyworks Solutions

On-chip

SAW Filter: Attenuation@40MHz=45dB Expensive Big area 2-3dB signal loss 1 Band = 1 SAW Filter

Typical Multi-standard RX-TX

Focus on:Relaxing RF filter requirements

15/12/105

* Ref: ISSCC2008 – E. Keehr * Ref: JSSC2007 – H. Darabi

• Linearity enhancement scheme with IM3 cancellation

Requirement of a very high linearity LNA!!!

Carrier signal

Blockers signals

• Translation feed-forward loop receiver

State of the art – On-chip interferer rejection

15/12/106

Wide-band Mixer Ampli BB Filter ADC LNA (Gmix) (Gamp)

Feedback Feedback FeedbackCurrent Mixer (Gmix) Filter (Gfil) I/Q Path

FLO

GLNA

gOTA

Idea: Translate BB filtering to RF input thanks to the feedback

BB-RF Feedback Receiver

• RF Filtering at the LNA input Blocker signals are attenuated

I/Q Path

15/12/107

Model of BB-RF Negative Feedback Receiver

RF Filtering at the LNA input

Matching to the antenna impedance in-band. Mismatching out-band

RF Central frequency = FLO

IN

BB

V

VG

OTALOBB

FBR gGmixffGfil

V

ifg )()(

)(

1)(

fgGi

VfZ

RFB

INFB

LNAFB

LNAFBIN ZfZ

ZfZfZ

)(

)()(

G: forward voltage gaingR: feedback loop transconductance gain

15/12/108

Mixer Ampli (Gmix) (Gamp)

Ampli Feedback V / I Mixer(Gmix)

FLO

LNA

gOTA

Voie I/Q

LPF

I/Q Path

-+

FLO

Low Pass filter configuration – Theorical Analysis

Open loop: ZIN=ZLNA > ZANT

fRF

Blocker signal

Carrier signal

1

1 )(1

)(

K

ffLZZ

fZLOBPLNA

LNAIN

Input Impedance Mathematical expression

fLOfBB

fRF

fRF

Close loop: ZIN(fLO) = ZANT

LPF

15/12/109

LPF Configuration – Simulation results

ZIN=50Ω

• Matching in-band (ZIN=50Ω) and mismatching out-band (ZIN>50Ω)• Over voltage for out-of-band signals in LNA input

Input Impedance Input Voltage

ZLNA=1KΩ

Over voltage

15/12/1010

Mixer Ampli (Gmix) (Gamp)

Ampli Feedback V / I Mixer(Gmix)

FLO

LNA

gOTA

Voie I/Q

HPF

I/Q Path

-+

FLO

High Pass filter configuration – Theorical Analysis

fRF

fLOfBB

HPF

fRFfRF

Blocker signal

Carrier signal

Input Impedance Mathematical expression2

2 )(1

)(

K

ffHZZ

fZLOBPLNA

LNAIN

Open loop: ZIN=ZLNA > ZANT (Image Frequency)

Close loop: ZIN(fLO) = ZANT

15/12/1011

HPF Configuration – Simulation results

• 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)

ZLNA=1KΩ

ZIN=50ΩAtt=2.5dB

Input Impedance Input Voltage

15/12/1012

Mixer Ampli LNA (Gmix) (Gamp)

Ampli Feedback V / I Mixer(Gmix)

FLO

GLNA

gOTA

Voie I/Q

LPF

I/Q Path

+

+

FLO

fRF fLOfBB

LPF

fRF

Blocker signal

Carrier signal

fRF

3

3 )(1

)(

K

ffLZZ

fZLOBPLNA

LNAIN

Input Impedance Mathematical expression:

Positive Feedback Architecture

Open loop: ZIN=ZLNA < ZANT

In-band signal enhanced

15/12/1013

Results simulation

• Matching in-band (ZIN=50Ω) and mismatching out-band (ZIN<50Ω)• Good attenuation. It depends of initial ZLNA

LNA

LNAANT

LOINANT

LOIN

Z

ZZ

fZZ

fZdBAT

)(

)(log20)(

3

3

ZLNA=10Ω

ZLNA=3Ω

Att=19dB

Input Impedance Input Voltage

15/12/1014

Stability Analysis

)(1)(1

)(fS

G

KffL

ZZZZ

GfG

LOFPB

LNAANT

LNAANTFB

11

KZZ

ZZ

LNAANT

LNAANT

Stability condition

For f=fLO:

• Stable for S1

• Unstable for S2

S2=-1.07

S1=-0.88(-1,0)

Feed-back Gain:

OTALNA gGampGmixGK

2

1

15/12/1015

Noise Figure

XS

X1

XA

XB

X2

XOA

B

+

+

A: forward voltage gain B: feedback loop voltage gainFA: NF of forward pathFB: NF of feedback loop

)1(1 22

222

2

21 BACL FBF

Xs

XB

Xs

XF

Forward path contribution

Feedback path contribution

15/12/1016

NFA B NFB NFCL

3.4 0.245 4.7 3.52

3.4 0.245 6.9 3.75

3.4 0.245 10.4 4.36

3.4 0.245 13.2 5.23

Application Example

For ZLNA=3: If A=36dB gR=4.9mS, B=gR*ZIN(fLO) = 0.245

With these values, S=-0.88>-1

NFCL to be compared to NF of SAW+ Typical Receiver

System is stable!!!

15/12/1017

• 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

Conclusions

15/12/1018

Thank you!!!