24
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

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

  • Upload
    others

  • View
    3

  • Download
    0

Embed Size (px)

Citation preview

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)

��������������������������������������������������������������������������������������������������������������������������������

��������������������������������������������������������������������������������������������������������������������������������

���������������������������������

���������������������������������

������������

���������������������������������

���������������������������������

���������������������������������

���������������������������������

���������������������������������

���������������������������������

��������������

��������������

������

������

������

������

������������

������������������������������������������������������������������������������������������������

������������������������������������������������������������������������������������������������

���������������������������������

���������������������������������

����������������������

����������������������

��������������

��������������

������

������

������

������

��������������������������������������������������������������������������������������������������������������������������������

��������������������������������������������������������������������������������������������������������������������������������

��������������

��������������

������

������

������

������

������������

���������������������

���������������������

���������

���������

���������

���������

���������

���������

���������������������

���������������������

���������������������

���������������������

���������

���������

���������

���������

��������

��������

��������

���������

���������

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