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
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• 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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!!!