power amplifier design and load pull - keysight · pdf filepage 46 amplifier research are the...

© Copyright Agilent Technologies and bsw 2013

Power amplifier design and load pull

measurements in practice Designing for RF Performance with Load-Pull Characterized Components

Herman Westra

Technical Consultant

Agilent Technologies

[email protected]

Gustaaf Sutorius

Application Engineer

Agilent Technologies

[email protected]

Remi Tuijtelaars

CTO

BSW Test Systems and Consulting

[email protected]


Agenda

10.00 – 10.20: Introduction: Why is load-pull important

10.20 – 11.00: Review of non-linear RF device models

11.15 – 12.00: Collecting measurement data: Setup Part 1

12.00 – 13.00: Lunch


13.30 – 14.30: Design, simulation and optimization with load-pull

data-based models

14.45 – 15.45: Circuit demonstrator and live measurements

15.45 – 16.30: Closure & Drinks


measurements in practice


(Large-Signal) transistor models overview

Compact

model

Behavioral

model

Physic

model

Physical insight

Operating range Convergence

Extrapolation

Accuracy

Easy modeling

process

Usability for Circuit design

Power amplifier design and load pull measurements

in practice


The compact model

• Equivalent, electrical schematic

– Schematic is fixed

– Component values are to be determined;

– … extracted from measurements.

• Typical measurements:

– (pulsed) IV measurements

– Small-signal S-parameters

• (use LP for verification!)


in practice


Sample Model Schematic


in practice


Collecting measurement data

A: Pulsed IV & Small Signal S parameters

B: Large Signal X-parameters & NVNA

D: Power Amplifiers

E: Impedance Tuning




Quiescent bias point

Pulse IV point

time

time

Pulsed IV Measurements


in practice


Pulsed Measurements = quasi isothermal operating conditions

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2

90

85

80

75

70

65

60

55

50

45

40

35

30

25

Central finger

Lateral finger

Pulsed IV


in practice


Pulsed Measurements = quasi isothermal operating conditions

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2

90

85

80

75

70

65

60

55

50

45

40

35

30

25

Central finger

Lateral finger

Why PIV measurements?

• (quasi) isothermal behavior


in practice


• Electrothermal behavior vs duty cycle:

DC bias

Not only the impulse

width, but also the

impulse repetition

affects self-heating

time time

Chip temperature

Chip temperature

DC bias

Temperature during PIV measurements


in practice


Traps


in practice


τcapture << t IMPULSION << τémission

During the pulses capture takes place, emission freezed

Gate-lag: decrease of drain current Drain-lag: increase of Vknee

Gate-lag

Green (Vgs0=0V,Vds0=0V)

Red (Vgs0=-4 V, Vds0=0V)

Drain-lag

Red (Vgs0=-3V, Vds0=0V)

Green (Vgs0=-3V, Vds0=30V)

Traps


in practice


PIV Meas.

Parasitic inductance

Parasitic Resistance

IV Calibration Transistor

Characteristic

DU

T

PIV Output PIV Input

50W 50W

Bias

T

Bias

T

Impedance

Stabilization

Network

Parasitics of the setup


in practice


Transistor + parasitic (Rs=0.3W)

resistance. Measurements

Transistor measurements

1 2 3 4 5 6 7 8 9 0 10

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.0

2.0

Vds (V)

Ids (

A)

If Serial and Parallel

resistances are not taken

into account, the

measurements lead to bad

knowledge of the “Ron”,

“Gm” and “Gd” transistor

characteristics

Effect of series resistance

• Use a DC calibration


in practice


Advantages:

• The component can be tested even in high power dissipated areas while

keeping the transistor in safe operating conditions

•Even if pulsed measurements do not provide pure isothermal

measurements, it provides measurements close to real life operating

conditions when the transistor is driven by RF power signals

• The thermal effects are characterized : influence of QP on Idss

• The trapping effects are highlighted (gate lag, drain lag)

• effect of parasitics of the setup must be removed.

Summary PIV measurements


in practice


Power Capabilities

•10A - 240V // 30A -120V // 30A-1kV

•100ns to 1,3ms pulse width

Safety

•Electronic fuse integrated in drain

and gate power heads

Accuracy & speed

•15 bits IV acquisition units embedded (no

need for external oscilloscope)

•Automatic calibration ports integrated

Flexibility

•PIV or Load-Pull drain power heads

Maury/AMCAD PIV system


in practice


Agilent B1500A/B1542A/B1505A

• Parameter analyzer

curve tracer

• Extremely accurate

• SMU approach

• B1505A: 10kV/1500A

Min pulse width: 10µs

• B1542A: 10V/80mA

Min pulse width: 10ns


in practice


Small Signal S-parameters

• Use VNA

• Avoid signal compression in device at ALL bias points

• Pulsed IV measurements,

• … then also pulsed S-parameters with pulsed DC-bias!


in practice


Pulsed S-parameters

Pulsed S-parameter measurements must not be noisy at low duty cycle with

narrow pulse width

Pulse detection methods

Wideband detection Narrowband detection

• No pulse desensitization

• Increased noise with narrow pulse width due

to wider IF bandwidth

• Limited pulse width by maximum available IF

bandwidth

• Narrower minimum pulse width than

wideband pulse

• Reduced dynamic range with low duty cycle

due to pulse desensitization by 20*log(duty

cycle)

IF filter IF filter Receiver samples Receiver samples


in practice


Dynamic range with narrowband detection at 500 ns pulse width

No Averaging, 1% smoothing on, 500 Hz IF bandwidth Hardware

gating

Crystal

filter

Software

gating

Spectral

nulling

>100 dB at 10%

>100 dB at 5%

90 dB at 1%

85 dB at 0.5%

PNA/PNA-X Noise reduction techniques and

performances


in practice





D: Power Amplifiers

E: Impedance Tuning




S-Parameters = linear = traditional VNA no harmonic distortion

X-Parameters vs S-Parameters

X-Parameters = nonlinear = NVNA also harmonic distortion


The Agilent Nonlinear Vector

Network Analyzer (NVNA)

system is based on the

company’s proven four-port

PNA-X microwave VNA and new

software in support of nonlinear

device measurements that

include X-Parameters

X-Parameters from measurements

http://www.google.ca/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=3uqsXCoAmQrAvM&tbnid=Iya4JatVxLj17M:&ved=0CAUQjRw&url=http://mwrf.com/test-and-measurement/microwave-vnas-add-nonlinear-network-analysis&ei=IkA6Uc6_MoS60AHoqIH4Bg&bvm=bv.43287494,d.dmQ&psig=AFQjCNGPpLFREv4x2y5v1UC3nZYsM7D4_Q&ust=1362858381984768


• 10MHz to 26.5GHz 4 port PNA-X with NVNA firmware options:

– Option 510 (Base NVNA FW)

– Option 514 (X-parameters)

– Option 520 (Load-dependent X-parameter extension)

2 x U9391C, 10MHz-26.5GHz

Comb Generator

1 x U2002A, 50MHz-24GHz

Average Power Sensor



The PNA-X/NVNA


The PNA-X/NVNA Generate Static LO



• Since we are using a mixer based VNA

the LO phase will change as we sweep

frequency. This means that we cannot

directly measure the phase across

frequency using unratioed (a1, b1)

measurements.

• Instead, we ratio (a1/ref, b1/ref) against a

reference signal that has a constant

phase relationship versus frequency and

from sweep to sweep.


Pulsed CW Measurement Conditions

• All measurements are performed under pulsed CW conditions:

– Carrier frequency = 1300MHz

– Pulse width = 100µS

– Duty cycle = 10%

• Pulse generators and pulse

modulators internal to the

PNA-X are used control the

RF pulse conditions




Rear panel pulse I/O

Enables the pulse hardware access externally

• The internal pulse modulator (s) can be pulsed externally

• The 4 pulse generator outputs can be accessed externally

• The internal narrowband IF receiver gates can be accessed externally

N1966A

Pulse I/O adapter


NVNA Pulse setup

Pulse generator 1: Masterpulse, triggers external multimeter

Pulse generator 2: Triggers RF signals. Triggers the modulator for PNA souce1 (Large Signal) and PNA source2 (Extraction Tone)


TTL Pulse 1: Yellow, TTL Pulse 2: Green, 1.3 GHz RF Signal: Blue

PNA Pulsed signals on 9000 Infiniium Oscilloscope 1 mSec/division


PNA Pulsed signals on 9000 Infiniium Oscilloscope 100 uSec/division


© Copyright Agilent Technologies 2013

PNA Pulsed signals on 9000 Infiniium Oscilloscope 2 nanoSec/division, 1.3 GHz RF CW signal visible



Measurement Setup

µW

Tuner

µW

Tuner

Part of U3020A

CGH40010F

in µW test fixture

Part of U3020A

N6705A

DC Power Analyzer

34411A

6½ Digit Multimeter

AR60S1G4 ZHL-16W-43+

DUT

PNA-X/NVNA controls all instruments and hardware in the

system as well as the complete X-parameter extraction procedure




Actual Measurement Setup at High Tech Campus Eindhoven




Measurement Setup: Voltage & Current for DUT

µW

Tuner

µW

Tuner

Part of U3020A

CGH40010F

in µW test fixture

Part of U3020A

N6705A

DC Power Analyzer

34411A



DUT

PNA-X/NVNA controls all instruments and hardware in the

system as well as the complete X-parameter extraction procedure




Measurement Setup: Voltage & Current for DUT (CREE CGH40010F RF Power GaN HEMT)




Analyzer is controlled

directly from NVNA

firmware using SCPI

Bias conditions are

automatically embedded into

measured X-parameter model

In-pulse Current Measurements Using the DC Power Analyzer

• Two N6705B DC power analyzer modules provide constant

gate and drain DC bias


Fixture Electrolytic Capacitors (ELCOs) and wire inductance

prevent accurate current measurements using the DC analyzer

Hall effect sensor (N2783A current

probe) is placed between

transistor drain and ELCOs to

take multiple in-pulse samples

The 34411A multi-meter and

average calculations are setup

directly in the NVNA firmware

In-pulse Current Measurements Using a Hall Effect Sensor N2783A + 34411A


In-pulse Drain Current Measurement

Drain Current is measured with the 34411A fast multimeter :

• 34411A is controlled by NVNA and triggered by the PNA-X P1 pulse generator

• 34411A measures 60 uSec inside the 100 uSec RF pulse from 20 uSec to 80 uSec

• 34411A measures 200 times the same pulse and calculates average (cal:stat:on;init;calc:aver:aver?)and returns this average value to NVNA/PNA


Measurement Setup: Power Budget

In General:

1. Aim for -20 dBm (or less) power at the PNA receivers and calculate

the required attenuators

2. X-parameter extraction tone 20dB below fundamental

3. Port1 signal could reflect 100% and add in-phase . Protect A1

receiver for this.


Power Budget: Actual attenuators used in setup

40 dB 30 dB

40 dB 20 dB

3 dB

43 dB

43 dB


Power Budget: Why 30 dB for R1 and 40 for A receiver?

40 dB 30 dB

40 dB 20 dB


+34dBm

+38dBm

+14dBm (ET) Part of U3020A

A

R1

Part of U3020A

18dB33dB

CF = 20dB

DU

T

R3

-19dBm

-19dBm

23dB 42dB

-20dBm -20dBm

CREE CGH40010F

Fc = 1300MHz

Power gain = 12dB (typ)

Pout = 13W (+41.2dBm)

C

+23dBm

+41dBm (ET)

Tu

ne

rT

un

er

+39dBm

+33dBm

+13dBm (ET)

+22dBm

(ET)

+42dBm

+22dBm (ET)

+42dBm

+33dBm

+13dBm

(ET)

+39dBm

20dB

CF = 20dB

CF = 20dBCF = 20dB

Port 1

Port 3

AR60S1G4

G = 47dB (typ)

Pmax = +48dBm

F = 0.8 to 4.2GHz

No

nlin

ea

r V

ecto

r

Ne

two

rk A

na

lyze

r

ZHL-16W-43+

G = 45dB (typ)

Pmax = +42dBm

F = 1.3 to 4.0GHz

-13dBm

-33dBm (ET)

-12dBm (ET)

10dB

Power Budget: calculation example


Measurement Setup: Power Amplifiers

µW

Tuner

µW

Tuner

Part of U3020A

CGH40010F

in µW test fixture

Part of U3020A

N6705A

DC Power Analyzer

34411A



DUT




Measurement Setup: Tuners

µW

Tuner

µW

Tuner

Part of U3020A

CGH40010F

in µW test fixture

Part of U3020A

N6705A

DC Power Analyzer

34411A



DUT

The Maury tuners are controlled by software on the PNA-X







D: Power Amplifiers

E: Impedance Tuning




Amplifier Research are the worlds largest manufacturer or RF and Microwave

Power Amplifiers.

AR Instrumentation Based In Souderton, Pennsylvania for over 40 years.

•Formed by Don Shepherd in his garage producing valve amplifiers for EMC

and Plasma generation.

•Don is still involved in the day to day running of the company.

•Now turning over >$70M and growing.

•AR Modular based in Bothel, Washington State

•Founded in 1971 as RF Power Labs

•Became Kalmus in 1985

•Acquired by Amplifier Research in 2001

•Now the market leader in Military booster amplifiers, narrow and broadband

custom amplifiers and modules.

OVERVIEW


PRODUCTS

•A Series DC – 400MHz, 25W – 50kW

•W Series DC – 1GHz, 1W – 4kW

•S Series 0.7 – 18GHz,1W – 1200W

•T Series 0.8 – 45GHz 10W – 10kW (TWT Based)

•E and H Field Measurement Probes

•Log Periodic and Horn Antennas

•Directional Couplers

•RF Components

•Software Control

•Custom Amplifiers and Modules.


AR Amplifier Specification

MISMATCH TOLERANCE

100% of rated power without fold back

Will operate without damage or oscillation with any magnitude and phase of

source and load impedance

With the wide range of applications for the AR amplifiers this mismatch

specification is extremely difficult to meet. Rarely do our amplifiers operate

into 50Ω. In EMC applications the load impedance can change from open to

short in a few MHz caused by reflections within the test chamber.


Compliance by design

RF Transistors – True Class A bias

• No chance to self bias

•Typically runs cooler under LS drive

•No concern with driving mismatches.

High efficiency devices (GaN, LDMOS)

•Cannot be biased in true class – A

•Requires judicious choice of bias point

•Relies on more robust bias control


Mismatch Testing

This is one of the high power 6 way

splitters used for varying the load

presented to the amplifier under test.


1-6GHz PA Module





D: Power Amplifiers

E: Impedance Tuning




1) Vary impedance presented to

DUT (active device, transistor)

2) Measure Pout, Gain,

Efficiency…

3) Determine best matching

impedance

4) Design matching network

(EEsof ADS)

Highest Pout

Collecting measurement data: Load-Pull

What is load-pull?


Impedances and impedance tuners

Airline

Probe

Airline

X YProbe

VSWR α Gamma α 1/Ω

10:1 VSWR = Γ=0.82 =

5Ω

20:1 VSWR = Γ=0.9 =

2.5Ω

Γ = a/b

Y

X


Traditional Load Pull, measures scalar power, with a power meter and does de-

embedded through S-Parameter block and pre-characterized Impedance Tuner(s)

(optional

)

Traditional/Classical load pull


Traditional load pull measures

scalar (input and reflected) power

and has no knowledge of the

vectorial relation, thus no

knowledge of the vectorial input

impedance.

Large signal input impedance, Zin,

changes as function of:

- Drive power

- Zload

Dissipative losses of an input tuner

can only be estimated due to lack

of knowledge of vectorial input

impedance.

Classic LP typically reports only

transducer gain accurately.

What about the input impedance


VNA-based/Vector-receiver/Real-time load pull

• Measure all a’s and b’s to and from the DUT, as

– vectorial ratio (~S-pars)

– absolute value (~power)

Impedance Tuner

Low-loss Coupler

Low-loss Coupler

Network Analyzer

Signal Source

Amplifier50Ω Load

Impedance Tuner


2 2 2 2

2 2 2

1 11

2 2out loadP b a b

2 2 2 2

, 1 1 1

1 11

2 2in del inP a b a

2 2

2

2 2, 1

1

1

loadout

p

in del in

bPG

P a

,out in del

DC

P PPAE

P


Impedance Tuner

Low-loss Coupler

Low-loss Coupler

Network Analyzer

Signal Source

Amplifier50Ω Load

Impedance Tuner


• Calculate/measure:

– transducer and operating-power gain.

– DUT Input impedance

– Load impedance !



Traditional LP Vector Receiver LP

Pre-

Characterization

Required Recommended (not

required)

Number of Points More points = greater

accuracy (even with

interpolation)

Minimum points required

(no impact on accuracy)

Tuner De-

embedding

Critical! (Accuracy

relies on de-embedding)

No tuner de-embedding

Power Sensor

Power Sensor

Spectrum

Analyzer

Power Meter

Impedance Tuner Impedance Tuner

Signal Source

Amplifier Impedance Tuner

Low-loss Coupler

Low-loss Coupler

Network Analyzer

Signal Source

Amplifier50Ω Load

Impedance Tuner

VNA-based vs classical load pull (I)


Traditional LP Vector Receiver LP

Verification

Procedure

ΔGt

complex conjugate

matched verification

Zin vs. Zload

comparison

ΔGt

complex conjugate

matched verification

VNA-based vs classical load pull (II)


VNA-based vs classical load pull (III)


Passive tuner matching limitations

Maximum Tuning Range (exaggerated for effect)

Losses of cables, probes, test fixtures reduces

tuning range and cannot be overcome using

traditional load pull methods

Tuner Tuner +

Cable

Tuner + Cable + Probe


Active and hybrid-active load pull

Airline

Probe

Airline

X YProbe

VSWR α Gamma α 1/Ω

10:1 VSWR = Γ=0.82 = 5Ω

20:1 VSWR = Γ=0.9 = 2.5Ω

Γ = a/b

Mechanical Tuner

Gamma comes from probe

(slug) inserted into airline

Γ<1

Active Tuner

Gamma comes from signal

generator and amplifier

Γ=1 or Γ>1


Active Fo Load Pull


Hybrid-Active Fo Load Pull


Gamma advantage of Active Load Pull Losses of

cables, probes, test fixtures reduces tuning range,

and can be overcome using larger amplifiers

Γ=0.99 Γ=0.99

Tuner + Cable + Probe



External Tuners

For Harmonic Load Pull, Traditional Load Pull systems require one mechanical tuner

per frequency per DUT side

To tune Fo, 2Fo and 3Fo at the same time requires 3 tuners (using multiplexer or

cascaded methods)

It is possible to build 3 tuners in 1 box, but it becomes 2-3x longer and 2-3x more

expensive

Active and hybrid-active harmonic load pull


Active Fo, 2Fo, 3Fo Load Pull



Passive Fo

Active 2Fo, 3Fo

Γ2Fo=0.988 @ DUT

on-wafer!

One of many configurations of hybrid/active load pull




Hybrid Active Fo, 2Fo, 3Fo Load Pull


LP for design of matching networks

• Set-up a load-pull sweepplan and store data.

• Import sweep-plan data in data object in ADS.

• and simulate …..


VNA Based load pull + PIV system is preferred for model validation

Specific Architecture

PA

VNA

Tuner f0, 2f0, 3f0

50W

DUT T T

Gate

Dra

in

DC or pulse DC supplies

+ meas Units

CW or pulse RF signal

f0 or f1+f2

Low loss directional

couplers

Tuner f0

Phase

reference

LP for model verification


meas.

model

-5 0 5 10 15 20 25-10 30

10

15

20

25

30

35

5

40

10

20

30

0

40

Pin dBm

Pout

(dB

m)

and G

ain

(dB

)

PA

E (%

)

PoutPAE

gain

0 5 10 15 20 25-5 30

0

20

40

-20

60

0

20

40

-20

60

Pin dBm

Po

ut (d

Bm

) a

nd

Ga

in (

dB

)

PA

E (%

)

meas.

model

Pout PAE

gain

Model validation of a 8x75 µm GaN HEMT with

load-pull measurements performed at 6 GHz

for optimum PAE load impedance in class-AB

Model validation of a 8x400 µm GaN HEMT with

load-pull measurements performed at 3 GHz for

the optimum Pout load impedance in class-B



Time domain load pull

measurements

Deembedding in the intrinsic

reference plane

Parasitic extrinsic elements must

be accurately extracted by previous

S parameter measurements

Large signal impact - class AB, 25V, 10 GHz – Comparison with measurements

With non optimal loads :



LP with X-parameters (behavior)

• Set-up a load-pull sweepplan and store data.

• Import sweep-plan data in X-parameter data object in ADS.

• Verify data with additional measurements/simulations

• Start the circuit design …..


Agenda

10.00 – 10.20: Introduction: Why is load-pull important

10.20 – 11.00: Review of non-linear RF device models


12.00 – 13.00: Lunch


13.30 – 14.30: Design, simulation and optimization with load-

pull data-based models

14.45 – 15.45: Circuit demonstrator and live measurements

15.45 – 16.30: Closure & Drinks

Designing for Optimal RF Performance with Load-

Pull Characterized Components

power amplifier design and load pull - keysight · pdf filepage 46 amplifier research are the...

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