An Overview of Power Amplifier Research at UCSD

Peter Asbeck

Lots of Watts and Plenty of MHz:An Overview of Power Amplifier

Research at UCSD

Power Amplifier Faculty & Researchers

RF Integrated Circuit Group

Prof. Larry Larson

Prof. Gabriel RebeizApplied Electromagnetics Group

High Speed Device GroupProf. Peter Asbeck

Prof. James BuckwalterHigh Speed Integrated Circuits Group

Don KimballCal IT2

Center for Wireless Communications

California Insitute for Telecommunications& Information Technology

Center for WirelessCommunications

Center for Wireless Communications

Center for WirelessCommunications

Wireless systems

Advancement of Wireless Communications

EfficiencyBandwidthIntegrability, low costMultiband, adaptivityLow noise / interference

Shannon limit R<B(log2(1+S/N))

Complex modulationHigh peak to average ratio

High bandwidthFuture: higher frequency High power

Low interference

Precvd ~ Ptrans * Gtrans*Grecvr* (do/d)n n~4Tyranny of free-space propagation

Transmitter power >> receiver powerPA dissipation is critical

Perversity of amplifier circuitsPAR and bandwidth are the enemies of efficiency!

Critical Factors for Future Wireless Systems

Challenges for Power Amplifiers

Agenda

Path to high efficiency & bandwidth in Base-station PAs

Handset PA development

Future technology opportunities

Critical problem for power efficiency:Varying signal power level

Power/Pave (dB scale)

Prob

abili

ty~8 dB peak to average power ratio

Class AClass B

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Effic

ienc

y

Average power

Class A

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1Pout (normalized)

Maximum power

EER/ET

0.0%

1.0%

2.0%

3.0%

4.0%

5.0%

-60 -50 -40 -30 -20 -10 0 10 20 30

P out (dBm)

Prob

abili

ty

Power Control Variation

Envelope Tracking (ET) Technique

Envelope Amplifier provides dynamic drain voltageMaximizes PA efficiency by keeping RF transistor

closer to saturation for all envelope amplitudes

EnvelopeAmplifier

Dynamic Drain VoltageDCSupply

RFSignal Out

Volta

ge

Time

RFSignal

In

RFAmplifier

EnvelopeDetector

Drain voltage tracks envelope

of RF signal

In Envelope Tracking, PA is quasi-linear.Input signal contains envelope and phase information.

Pout (dBm)

Effic

ienc

y

Vcc1Vcc2

Vcc3 Vcc4 Vcc5

ET System Maximizes Efficiency Vs Power By Adjusting Output Bias (Vcc or Vdd)

Schematic Dependence of Efficiency on Output Power

EfficiencyFor ET system

DAC

DC/DC

Drivers

DC

UpconDAC

Drain Modulator

WCDMA

RFOutput

Envelope

PAFinal stage

ET/E

ER a

ndPr

edis

tort

ion

DSPI

Q

DownconADC

Experimental Envelope Tracking Amplifier

High PowerRF Stage

F= 2.1 GHz

Complex system includingRF stage, analog/digital dynamic power supply, digital predistortion, up and down-converters

X1=0

Harmonic Load TuningSimulated Efficiency vs Harmonic Load Reactance

Class F-1

Class F-1Class F

Class FClass B

Envelope Amplifier Design

EnvelopeSignal

CurrentSense

RF Power Transistor Drain Bias

LinearStage

VDC

SwitcherStage

Voltage SourceHigh BWEff = 50%

Current SourceLow BW

Eff > 90%

Envelope Amplifier: Overall Efficiency >70%BW = 50 MHz

VDC

Kimball

Signal generation Switcher controlTime alignment

DSP

EnvelopeSignal

CurrentSense

RF Power Transistor Drain/Collector Bias

LinearStage

VDC

Switcher

Voltage SourceHigh BW

Current SourceLow BW

VDC

iL1iLN iRVR

Vsw1

VS

L1D1 isw1

Main Switcher VDC Current SourceMedium BW

iL2

Vsw2

L2 D2

isw2

L2 < L1

Aux

DSP-driven Main switcher provides high slew rate currentAux switcher compensates DC error between Linear stage and Main switcher

Improved Envelope Amplifier Design

[dBc] ACPR1 ACPR2 NRMSEBefore DPD -35.4 -45.5 6.8%

After ML DPD -45.3 -50.7 2.4%After Memory

mitigation-55.5 -60.2 0.7%

ET PA with Dual Switcher / HVHBT PA

PDF

CE Gain PAE RF PA Envelope Amplifier

65.6% 12.3dB 61.7% 82% 80%

WCDMA6.6 dB PAPR

Before DPD

After DPD

After Memory Mitigation*

Record

Efficiency

Probability

Pout=67W

ET System: Path to Wider Bandwidth

EnvelopeAmplifier

DCSupply

RF Signal Out

Amplitude

RFPowerAmplifierRF Signal In

(WiMAX, 3GPP LTE)

Enough Bandwidth

Trade-off

Efficiency vs BandwidthDoesn’t need to be exact replica of input envelope as long as it does not clip output envelope

Vdd

New envelope: Power spectrumNew envelope: time domain

time frequency

Mark-II PA Digital Predistortion Testbench100 MHz Instantaneous BandwidthTunable Carrier: 100 MHz to 4.0 GHz

Can be extended to mm-waves using additional up/down converters

210 MSamples/s 14-bits DACs & ADCs52 MHz Digital IF (no I/Q impairments)Up to 220 data vectors (5-ms sequence length)

Can operate in EER, ET, or linear mode

Memory effect compensation available

Fully coded in Matlab, to allow development of new DPD algorithms

Digital Correction of Amplifier Output

|Vout| vs |Vin|

No correction Memoryless correction Full correction(with memory effect)

Measurements for commercial WLAN amplifier

Nonlinearity and "memory effect" must be mitigated in order to achieve signal accuracy needed for complex signal constellations

Input voltage (normalized) Input voltage (normalized) Input voltage (normalized)

AgendaPath to high efficiency & bandwidth in Base-station PAs

Handset PA development How to make a CMOS PAHow to make a mostly digital PA

Future technology opportunities

Stacked-FET Structure

0.2 0.4 0.6 0.80.0 1.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

4.0

time, nsec

Vgs

1, V

Vds

1, V

Vgs

2V

ds2

Vgs

3V

ds3

Vds, i

Vgs, i

Vds and Vgs swing of each FET

All FETs are operating in the safe region

34-dBm 4-Stacked PA in SOI CMOS

0.28-μm SOI CMOS process(S T Microelectronics)

Total device width = 5 mm x (4 devices) Chip size (include pads) = 0.43 x 1.56 mm2

Rload=11 ohms

In

RL

VG4

VG3

VDD

VG2

VG1

Cm1

Cm2

C2

C3

C4

m1

m2

m3

m4

Cm3

Cm4

Cm5

Cf

Rf

TL1

TL2

TL3TL4

TL5

TL6

TL7TL8

In

RL

VG4

VG3

VDD

VG2

VG1

Cm1

Cm2

C2

C3

C4

m1

m2

m3

m4

Cm3

Cm4

Cm5

Cf

Rf

TL1

TL2

TL3TL4

TL5

TL6

TL7TL8

In InIn In

OutOutOutOut GND

GNDGNDGNDGNDGND

GNDGNDGNDGND

VG2

VG4

VG3

GND

Gate capacitors

CWC Project withS T Micro

4-Stacked CMOS PA Performance with 1.9GHz WCDMA signal

High powerGood efficiencyGood linearity

Meets spec (-33dBc ACLR1)29.4 dBm output powerPAE=41.4 %

Comparable to GaAs HBT PAs

VDD=6.5V

On-Going Research in CMOS Envelope Amplifierfor LTE Handset Applications

Linear Stage

Switching Stage

Sense & Control

A combined class-AB and switch-mode regulator based supply modulator with a master-slave architecture is used to achieve wide bandwidth and high efficiency

Anti-shoot Through &

Gate Drivers

M6

V DD

L

M1

M2

M4

M3

OTA

Env_in

To PA

Rsen

M5

OP AMP

c

idia

R2R1

RL

Q1 Q2

Q3

Q4

BuckConverterw/ PWM

SwitchedResonator

(ωres)PM

AM

DSP

Digital Envelope-Tracking CMOS Handset Switching Mode Power Amplifier

Multi-mode, Multi-band

Digital PA Techniques- RF pulse modulation- Unit-cell switching- Charge sampling regulator 0.01

0.1

1

10

100

-10 0 10 20 30 40

Output Power (dBm)

Tota

l Effi

cien

cy (%

)All Cell, PWM1/10 Cell, PWM1/10 Cell, CMReference

15dB back-off

x2.4

850MHz

1.9 1.91 1.92 1.93 1.94 1.95 1.96 1.97 1.98 1.99 2-110

-100

-90

-80

-70

-60

-50

-40

-30

Frequency (GHz)

Pow

er/fr

eque

ncy

(dB

/Hz)

Slew ImpairmentNo Phase CorrectionSlew ImpairmentPhase PDM CorrectionNo Slew ImpairmentNo Phase Correction

1.9 1.91 1.92 1.93 1.94 1.95 1.96 1.97 1.98 1.99 2-110

-100

-90

-80

-70

-60

-50

-40

-30

Frequency (GHz)

Pow

er/fr

eque

ncy

(dB

/Hz)

Slew ImpairmentNo Phase CorrectionSlew ImpairmentPhase PDM CorrectionNo Slew ImpairmentNo Phase Correction

Slew ImpairmentNo Phase CorrectionSlew ImpairmentPhase PDM CorrectionNo Slew ImpairmentNo Phase CorrectionACPR improve

CWC Project with Panasonic

Bin.-to-Therm. Decoder

Amplitude Control Word

TunableMatchingCircuit

Vdd

ModulatedSignal

Phase-modulatedSignal

127 Unit Cells

3 Binary Cells

1 x

1 x

1 x

1/2 x

1/8 x

DPA core

Decoder

Decoder

Input Output

0

10

20

30

40

50

60

70

80

-20 -10 0 10 20 30

Output Power [dBm]

Pout

/Pdc

[%]

Vdd = 2.1 V, throughVdd = 1.5 V, throughVdd = 1.0 V, throughVdd = 0.5 V, throughVdd = 2.1 V, input attenuationVdd = 1.5 V, input attenuationVdd = 1.0 V, input attenuationVdd = 0.5 V, input attenuation

Digitally-Modulated CMOS PAPower controlled by number of "on" transistors

CWC Project with S T Micro

DPD Application to Skyworks GaAs HBT WCDMA PA Module

• 4mm x 4mm handset PA module, experimental variant of SKY77174 optimized for operation at 1.95GHz

• Features high linearity (better than −40 dB ACPR) up to 29 dBm in WCDMA mode

WCDMA3.3 dB PAPR–20 … 6 dBm1.95 GHz

50 Ωload(nominal)

Currentreading

Interstagematch

Outputmatch

bias and gain control

DA PA

3.4 V(nominal)

Module

Inputmatch

MMIC

|Vo,sat|

WCDMA Performance Using Digital PredistortionPerformance at high power

Average power consumption assuming CDMA power usage profiles

Hig

h Po

wer

Pe

rfor

man

ceAv

erag

e Pe

rfor

man

ce 371

189

454

269

0

100

200

300

400

500

600

Original PA Module Retuned PA w/ DPDAve

rage

Pow

er C

onsu

mpt

ion

(mW

)

UrbanSub-urban

Power Savings ~ 180mW

Agenda

Path to high efficiency & bandwidth in Base-station PAs

Handset PA development

Future technology opportunitiesAdaptive PAsBroadband PAsHigh frequency PAs

n-GaN layerTi/Au/Pd/Au

n+GaN layer

c-Sapphire

InGaN layer GaN cap layer

Ni contact

GaN buffer layer

-σ+σ

Wm

ax

W

High Q High Voltage Varactors for Adaptive PAs

GaN is 40x better than Si for high voltage varactor

UCSD Varactor ObjectivesHigh voltage (>100V)Low Rseries=> High Q for basestations (>150)& design for high linearity

GaN Single-Chip Broadband Amplifier

Simulated Drain Eff.

Measured Drain Eff.

Simulated PoutMeasured Pout

Ranges from 41 dBm to 41.7 dBm

Ranges from 54.4% to 76.6%

C1C1RF

CF

Stack GaN for higher Zout, higher power>12W out single chip!Efficiency ~60% 400MHz to 1.8GHz

What's Coming in GaN: On-going Research in Scaled Devices

HRL Laboratories

Lg=40nmFmax=400GHz

BV~42V

Quartz antenna bonded

on a SiGe chip

DigitalPredistorter DAC

Upconverter

downconverterADCVinMem

VoutMem

DSPAdaptation

LUTDig

ital

Bas

eban

d M

odul

ator

Dat

a in am

plifier/antenna array

Signal Generator

DSP

SiGe HBT &45nm CMOS SOI

UCSD mm-Wave Power Amplifier Arrays

Program goals: 4W at 45GHz1W at 94 GHz0.25W at 138GHz

All Si technology

40-60% efficiency

Measured 3×3 W-Band Power Amplifier

Quartzedge

RF Input

EIRP > 34 dBm at 90 – 99 GHz (@ 2.0 V)

•Array can be scaled to entire wafer, achieving EIRP in the MW range•Scanning phased arrays possible with incremental modifications

Dramatic increase in radiated power density

SummaryUCSD has a wide variety of projects for handset and basestation PAs

multiple technologies, frequencies & power levelsCMOS / HBT / GaN

UCSD has expertise in Digital Predistortion Techniquesalong with state-of-the-art test benches

State-of-art research is on-going in Envelope Tracking for both Basestation and Handset PAs

=> critical to the future of high performance PAsfor signals with high PAR (eg LTE!)

Hear more details at this afternoon's sessions!