Real-time Adaptation to Antenna

Impedance Mismatch for CDMA

Transceivers

Dongjiang Qiao, *David Choi, Yu Zhao, **Dylan Kelly,

Tsaipi Hung, Donald Kimball, Mingyuan Li, and Peter Asbeck

University of California, San Diego*Nokia Research Center, **Peregrine Semiconductor

Outline

Introduction

Design of Tunable Matching Network

Antenna Load Impedance Measurement Using Sectioned

Transmission Line

Closed-loop Measurement Results

Conclusions

Introduction

-1 dBVSWR = 4:1 VSWR = 10:1

PA Duplexer Antenna Switch Antenna

TX

RX

VSWR at antenna ref. plane can vary up to 10:1 with any phase.

It is a challenge to maintain optimum operation of the transmitter with such a wide range of impedance.

Performance of PA with Different Load

ADS simulation results for a class AB amplifier designed for 50 ohm

Mismatch Also Impacts:Stability: Possible oscillation of power

amplifier thus damaging the amplifierDuplexer insertion loss

5 10 15 20 25 30 350

5

10

15

20

25

Gai

n (d

B)

Pout (dBm)5 10 15 20 25 30 35

0

20

40

60

80 50 ohm 12.5 ohm 200 ohm

PA

E (%

)

Pout (dBm)

5 10 15 20 25 30 35-50

-40

-30

-20

IMD

3 (d

Bc)

Pout (dBm)

Adaptive Transmitter

PA Duplexer

Antenna

Controller

TX

RXLNA

Impedance measurement

Tunable matching network

Tunable Matching Network With Silicon-on-Sapphire Switches

L1 L2

C1 C2

L1 L2

C11 C22C12 C13 C21 C23

S21 S22 S23S13S12S11

– Stack of 6×6 parallel available – W/L = 6000um/0.5um per FET– Ron and Coff scale linearly with stacking /

adding parallel devices– BVDSS (2 nA/um) = 2 V– Recommend +/- 2 to 3 V bias– Ron = 0.5 ohm (2.75 ohm-mm) @ 3 V– Coff = 1.8 pF (300 fF/mm)– Gate is ESD protected

Compared to bulk CMOS, SOS has:Reduced component-substrate

parasitic capacitanceImproved isolation between

transistors

Characteristics of Tunable Matching Network

Average VSWR Reduction by

Tunable Matching Network

0 2 4 6 81.0

1.2

1.4

1.6

1.8

2.0

VSW

R w

Cor

rect

ion

VSWR w/o Correction

Available impedance of the tuner

Linearity and Insertion Loss

For switch setting close to 50 Ω, insertion loss ~ -0.36 dB. Could be reduced further if tuned to 50 ohm

Maximum available gain varies for different switch settings. Average maximum available gain ~ -0.25 dB.

Without TunableMatching Network

ACPR = -59.5 dBc ACPR = -59.2 dBc

With Tunable Matching Network

No harmonic generation observed

Class A PA

CDMA IS-95, 29 dBm

Signal Generator Spectrum

Analyzer

(for the switch setting close to 50 Ω)

Measurement of Load Impedance Using Transmission Line

( ) [ ]zjzjo eeVzV ββ Γ+= −+

0.5 1.0 1.5 2.00.0 2.5

-0.5

0.0

0.5

-1.0

1.0

time, nsec

ts(V

2), V

0.5 1.0 1.5 2.00.0 2.5

-0.5

0.0

0.5

-1.0

1.0

time, nsec

ts(V

1), V

0.5 1.0 1.5 2.00.0 2.5

-0.5

0.0

0.5

-1.0

1.0

time, nsec

ts(V

out)

, V

+

-ZL

ILV(z), I(z)

Z0, β

z1z2z3

zjo eV β−+

zjo eV βΓ+

Z0 = 50 ohm, ZL = 15 ohm, 90o Transmission Line

0

0ZZZZ

L

L+−

=Γ LCw=β

22

11

2

1zjzj

zjzj

z

z

eeee

VVr ββ

ββ

Γ+Γ+

== −

−

Measurement results depend on voltage ratios, not the voltages

Independent of input power and the source impedance

Measurement Setup

Fabricated on PCB board¼ λ transmission line815 MHzSingle tone and CDMA IS-95

Measured by Network AnalyzerMeasured by Transmission Line

CDMAThree input power levels (12, 14 and 16 dBm)

Load Impedance Measured by Artificial TL

Coilcraft inductors (Q > 100)CDMA IS-95

Part of the error was caused by the fact that the lumped elements do not have the same values as calculated for the artificial transmission line

0.65 0.70 0.75 0.80 0.85 0.90 0.950.60 1.00

-0.40

-0.35

-0.30

-0.25

-0.45

-0.20

freq, GHz

dB

(S(2

,1))

m4

m4freq=dB(S(2,1))=-0.331

815.0MHz

Z0

45o 45o

LL4

R=L=6.9 nH

CC6C=1.62 pF

CC5C=1.62 pF

CC4C=3.24 pF

LL3

R=L=6.9 nH

Measured by Network AnalyzerMeasured by Transmission Line

PA with Closed-loop Control

CDMA PA

Controller

Impedance measurement

Tunable matching network

Mechanical Tuner

Feedback Path Signal Generator

SpectrumAnalyzer

Control logic: voltages ratios are tuned close to 1 by changingswitch settings (load impedance close to 50 Ω)

GPIB interface controlled by LabView

Skyworks CDMA Handset PA CX77105 (GaAs HBT)

IS-95, 824MHz, Fixed 0 dBm Pin (~ 28 dBm Pout for 50 Ω)

Experimental Setup

Improvement of Power Amplifier Performance

Average results for VSWRs with different phase

1 2 3 4 5 6 7 8

12

16

20

24

28

0

10

20

30

40

50

Pout

w/o correction w/ correctionPo

ut (d

Bm

)

VSWR

PAE

PA

E (%

)

w/o correction w/ correction

1 2 3 4 5 6 7 8

-50

-40

-30

-20

-10

0

AC

PR fo

r wor

st c

ase

VSWR

w/o correction w/ correction

For 8:1 VSWR

–Pout improved by 2.8 dB

–PAE improved by × 2 times

–Worst ACPR reduced 4 dB

Impact of Load Impedance Mismatch on Duplexer(EPCOS B4224 SAW Duplexer Filter: Measured Data)

ZL = 50 Ω, Receiving Band

0.75 0.80 0.85 0.90 0.950.70 1.00

-60

-40

-20

-80

0

freq, GHz

dB

(S(1

,2))

m2m3

m2freq=dB(S(1,2))=-2.973

894.0MHz

m3freq=dB(S(1,2))=-2.756

869.0MHzReceivingPort I Mechanical Tuner

TransmissionPort IIIterminated with 50 Ω

AntennaPort II

ZL

Mechanical TunerTunable Matching Network

VSWR Correction

0.8 0.90.7 1.0

-40

-20

-60

0

freq, GHz

dB(S

(1,2

))

m2

dB(u

nc..

S(1

,2))

m3m2freq=dB(S(1,2))=-4.896

869.0MHz

m3freq=dB(unc..S(1,2))=-8.453

869.0MHz

Average results for 8:1 VSWR

–S12 ↑ 2.5 dB

Summary

Antenna load impedance mismatch has been effectively reduced using a tunable matching network implemented using SOS switches.

A method has been developed to measure the antenna load impedance based on measurement of the voltages along a transmission line.

With closed loop correction of the impedance mismatch, the output power, PAE and linearity of a PA have been improved; the in-band insertion of duplexer has been reduced.