Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford...

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FA 8.1: A 115mW CMOS GPS Receiver D. Shaeffer, A. Shahani, S.S. Mohan, H. Samavati, H. Rategh M. Hershenson, M. Xu, C.P. Yue, D. Eddleman, and T.H. Lee Stanford University

Transcript of Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford...

Page 1: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

FA 8.1: A 115mW CMOS GPS Receiver

D. Shaeffer, A. Shahani, S.S. Mohan, H. Samavati, H. Rategh

M. Hershenson, M. Xu, C.P. Yue, D. Eddleman, and T.H. Lee

Stanford University

Page 2: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

OVERVIEW

� GPS Overview

� Architecture

� Circuits� Experimental Results

� Summary

Page 3: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

GPS OVERVIEW: TYPICAL RECEIVER ARCHITECTURES

Distinguishing Features:

� Typical on-chip PD

is 100mW – 500mW

� Off-chip LNA oractive antenna

� Off-chip IF filtering

� 1 or 2 bit quantization

PLL

Off-Chip

2

1- OR -

Dual-Conversion

2

PLL

Off-Chip

Single-Conversion

Page 4: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

GPS OVERVIEW: SIGNAL STRUCTURE

� C/A code is a BPSK, D.S. spread-spectrum signal. Tc = 1�s, Tb = 20ms.

� Large processing gain. Gp = 10 log�

TbTc

�= 43dB

� Important fact: SNR� 0 dB at antenna! (PR � -130dBm)

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Subsequent image

this sideband.rejection suppresses

~ 20dB (Tr = 290K)Channel FilterGPS C/A Code

GPS P-Code

1.57542 GHz

2 MHz20MHz

-12 MHz -8 MHz -2 MHz 2 MHz 12 MHz8 MHz

2 MHz

Thermal Noise Floor

DownconvertIF RF

Page 5: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

ARCHITECTURE: LOW-IF RECEIVER

Primary Goal: Make choices to minimize PD, maximize integration.

� Low-IF) On-chipactive channel filter.

� Image in GPS band )

Relaxed I/Q matching.

� Eliminate PLL prescaler

) Saves power / noise.

� 1-bit quantizationfor simplicity.

BandGap

π/2

M*f0

N*f0

I[n]

Q[n]

PLL(M=17)

(N=23)

f0=4.024MHz

2.036MHz

Signal Path

1.57542GHz

APD

APD=1.573384GHzN*M*f0

Page 6: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

ARCHITECTURE: WEAVER IMAGE REJECTION

Question: Can we use 1-bit quantization in an image-reject architecture?

Key: Show that summing the two output channels yields 3dB improvement.

BA

+

-

I

Q

n(t)

I

Q� A: �IQ(t) = sgn [sin(2!t)]

� B: �IQ(t) = 0

� I/Q channels are de-correlatedafter the lowpass filter!

Answer: Yes, if the noise has equal sidebands and SNR � 0 dB. (As in GPS.)

Page 7: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: LNA / MIXER

Vb

LOp LOm

RFm

IFA

Ibias

RFp

LNA Mixer

1550 1560 1570 1580 1590 1600Frequency (MHz)

2.0

2.2

2.4

2.6

2.8

3.0

Noi

se F

igur

e (d

B)

Measured LNA Noise Figure

NF = 2.4dB @ 1575MHz

Ibias = 4.9mA

Shahani, Shaeffer and Lee, ”A 12mW Wide Dynamic Range CMOS GPS Receiver,” ISSCC 1997

Page 8: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: IFA

� Low input capacitance, high linearity.

� Load resistors terminate the active filter input.

Inp InmM1

M3

Ibias

Outp

M4

M2Outm

Ibias

-0.2 -0.1 0.0 0.1 0.2DC Input Voltage (V)

-40

-30

-20

-10

0

10

20

30

Vol

tage

Gai

n (d

B)

Simulated IFA Voltage Gain

Page 9: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: GM-C FILTER (ARCHITECTURE)

� Design based on a 5th-order L-C elliptical prototype.

� The dynamic-range limiting block in the system.

Gy Gy Gy Gy

Bias CircuitReplica

Gyrators (2 Transconductors, ea.)

IFA

Gm

Gm-C Filter (LC Ladder Prototype)

Page 10: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: GM-C FILTER (DESIGN APPROACH)

The filter is the most critical signal path element, and therefore requires the mostattention to detail. Some relevant ideas:

� Interesting fact: Fmin = 2 (1 + N). Independent of filter Z0!This implies a fixed amount of power gain to suppress filter noise.

� Fixed GP ) AV /p

Z0.Need to minimize Z0 to maximize dynamic-range.

� Seek linearization techniques that maximize Gm=Ibias .One sub-optimal approach would be linearization by degeneration.

� Use Class-AB techniques, if possible, to maximize power efficiency.

In short: It all depends on the transconductor!

Page 11: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: GM-C FILTER (TRANSCONDUCTOR)

Use two square-law transconductors to build a linear, class-AB transconductor.A little positive feedback (M10) compensates for mobility degradation in M1.

M2

M10

M1

M5Ibias

M6

Inp InmOutp Outm

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4DC Input Voltage (V)

0.90

0.95

1.00

1.05

1.10

Rel

ativ

e G

m

Simulated Gyrator Transconductance

With Positive FB (M10)Without Positive FB+/- 10% M10 Variation

Page 12: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: PLL OVERVIEW

A research goal: Explore techniques that reduce PLL power consumption.

� Maximize Q of spiral inductors in RF section.

) Use patterned ground shields (PGS). (Also aids isolation.)C.Yue and S. Wong, ”On-chip spiral inductors with patterned ground shields for Si-based RF IC’s,”

VLSI Symposium, 1997

� Prescaler consumes a large amount of power, and generates noise.

) Eliminate prescaler by only doing phase comparisons during periodic“apertures” positioned around reference edges. This saves power andreduces switching noise.

� Accomplished with an “Aperture Phase Detector” (APD).

Page 13: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: APERTURE PHASE DETECTOR (APD)

� Aperture opens when pre-charge period ends.

� Aperture closes when the first edge arrives, discharging the circuit.

ApertureOpens

DelayedReference

(Implicitly)

ApertureCloses

REFin

D

U

LOin

FFE1

FFE2

FFE3 Delay

ApertureTiming Diagram

t

DelayLOin

Phase Error

Problem: Loop can lock to any harmonic of reference!

Page 14: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

CIRCUITS: PLL ARCHITECTURE

An interesting idea: With dual APDs, the loop should lock to the least-commonharmonic of the two references.

� Works in theory, if APDdetects frequency.

� Problem in practice:APD only detects phase.

) Acquisition problem.

� Better solution:Use acquisition aidplus APD.

fRF=15*f0

Apertures

f2=3*f0

f1=5*f0

1 period of f0

Example: N=5, M=3

N*M*f0 I

Q

f1=N*f0

f2=M*f0

PLL Architecture

Page 15: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: FREQUENCY RESPONSE

0 5 10 15 20Frequency (MHz)

-80

-60

-40

-20

0F

requ

ency

Res

pons

e (d

B)

Signal Path Frequency Response

I ChannelQ ChannelSimulated

1.0 3.5

01

-3

Passband Detail

Page 16: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: NOISE FIGURE

1.0 1.5 2.0 2.5 3.0 3.5 4.0IF Frequency (MHz)

3.0

6.0

9.0

12.0N

oise

Fig

ure

(dB

)

Coherent Receiver Spot Noise Figure(Pre-Limiter)

Fine Quantization1-bit Quantization

Page 17: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: LINEARITY

-45 -40 -35 -30 -25 -20 -15 -10Input Power (dBm)

-80

-60

-40

-20

0

20

40O

utpu

t Vol

tage

(dB

Vrm

s)

Signal Path 3rd Order Intermodulation

Slope=3

Page 18: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: BLOCKING PERFORMANCE

0 10 20 30 40 50 60Offset Frequency (MHz)

-60

-50

-40

-30

-20B

lock

ing

Sou

rce

Pow

er (

dBm

)

Receiver 1-dB Blocking De-Sensitization(No Front-End RF Filter)

INMARSATUplink Band

Page 19: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: PLL SPURIOUS

1475 1525 1575 1625 1675Frequency (MHz)

-80

-70

-60

-50

-40

-30

-20

-10

0

10R

elat

ive

Pow

er (

dBc)

PLL Spurious

INMARSATUplink

f1 f2

f1-f2

Page 20: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: PLL PHASE NOISE

104

105

106

107

108

Offset Frequency (Hz)

-140

-130

-120

-110

-100

-90N

oise

Pow

er D

ensi

ty (

dBc/

Hz)

PLL Phase Noise

HP8780A

HP8664A

PLL

Page 21: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: OUTPUT SPECTRUM

0 1 2 3 4 5 6 7 8Frequency (MHz)

-120

-100

-80

-60

-40

-20

0M

agni

tude

(dB

FS

)

Receiver Output Spectrum(Pre-Correlation)

HP8664ASpur

Page 22: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

EXPERIMENTAL RESULTS: CODE CORRELATION

-512 -384 -256 -128 0 128 256 384 512Code Phase

0.000

0.005

0.010

0.015

0.020N

orm

aliz

ed C

ross

-Cor

rela

tion

Mag

nitu

de

Non-Coherent Receiver OutputGold Code Cross-Correlation

SNR = 15dB

Page 23: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

PERFORMANCE SUMMARY

Signal Path Performance PLL PerformanceLNA Noise Figure 2.4dB Loop Bandwidth 5MHzLNA S11 � -15dB Spurious Tones � -42dBcCoherent Receiver NF 4.1dB VCO Tuning Range 240MHz (� 7.6%)IIP3 (Filter-limited) -16dBm @ -43dBm Ps VCO Gain Constant 240MHz/VPeak SFDR 57dB LO Leakage @ LNA < -53dBmFilter Cutoff Freq. 3.5MHzFilter PB Peaking � 1dB Power/TechnologyFilter SB Atten. � 52dB @ 8MHz Signal Path 79mW

� 68dB @ 10MHz PLL / VCO 36mWPre-FilterGp 19dB Supply Voltage 2.5VPre-FilterAv 32dBTotalGp � 82dB Die Area 11.2mm2

TotalAv � 107dB Technology 0.5�m CMOSNon-Coherent Output SNR 15dB

Page 24: Stanford Universitysmirc.stanford.edu/papers/isscc98s-derek.pdf · 2009-08-19 · Stanford University. O VERVIEW GPS Overview Architecture Circuits Experimental Results Summary. GPS

ACKNOWLEDGMENTS

Rockwell InternationalDr. Christopher HullDr. Paramjit Singh

Tektronix, Inc.Ernie McReynolds

Defense Advanced Research Projects Agency