STAN Tool overview

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STAN Tool

Stability Analysis of Microwave

Circuits

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Frequency (MHz)

Ou

tpu

t p

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dB

m)

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Frequency (MHz)

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(dB

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Frequency (MHz)

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(dB

m)0 oscillation

2f

low frequency

oscillation

Oscillations in RF Power Amplifiers

- low-frequency oscillations, often

linked to bias networks, can be

detected using small-signal

simulations

RF Power Amplifiers are prone to (unwanted!) oscillations

- parametric oscillations function of

the input drive signal, have to be

detected in large signal

Typical ones:

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Linear analysis “small signal”

– K factor

– Normalized Determinant Function

(NDF)

– Stability envelope

Non-linear analysis “large signal”

– Nyquist criterion

– NDF

– Bolcato, Di Paolo & Leuzzi,

Mochizuki, …0 200 400 600 800 1000 1200 1400 1600

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tpu

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Frequency (MHz)

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tpu

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(dB

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Frequency (MHz)

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tpu

t p

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(dB

m)

0 oscillation2

f

low frequency

oscillation

Existing Methods

Either not complete or too complex !!!

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Existing Methods

Linear analysisWidely used: K factor (also µ and µ’ now)

- K>1 & |∆| <1: unconditional stability of two port network

- K<1: conditional stability stability circles

Unconditional stability Conditional stability Unconditional instability

Only indicates that a stable circuit will continue to be stable when loading it with

passive external loads at the input or output

Do not guarantee the internal stability of the circuit !

Limitations:

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Existing Methods

INOUT Gate Drain

Sourc

e

Multi-stage power amplifier Multi-fingers transistor

Linear analysisPotentially instable architectures for which K factor is not

enough

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Objectives:

- Detect potential oscillations

- Get knowledge on oscillation

localization and oscillation mode

- Apply suitable stabilization strategy

How to avoid parametric oscillations in combined amplifiers ???

Manufacture PAs with confidence

(and performances!)

Oscillations in RF Power Amplifiers

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-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3-6

-4

-2

0

2

4

6

Re (GHz)

Im (

GH

z)

Pole-Zero Identification

Node ‘n’

in s( i ,f )outv

RG

f0,

Pin

RL

10

30

-10

50

dB

(Zsond)

2.0E9 4.0E9 6.0E9 8.0E9 1.0E100.0 1.2E10

-100

0

100

-200

200

frequency

phase(Z

sond)

Freq (GHz)

|H|

(dB

)

H (

º)

poles

zeros

Pole-zero plot

( )H j

1

1

( )

( )

( )

n

i

i

p

j

j

s z

H s

s

Frequency

domain

identification

techniques

STAN Tool

Complex conjugate poles with positive real part -> start-up of an oscillation

Oscillation frequency = Module of the imaginary part

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STAN Tool

J.M. Collantes et al. “Monte-Carlo Stability Analysis of Microwave Amplifiers”, 12th IEEE

Wireless and Microwave Technology Conference, April 2011, Florida.

A. Anakabe et al. “Automatic Pole-Zero Identification for Multivariable Large-Signal Stability

Analysis of RF and Microwave Circuits”, European Microwave Conference, September

2010, Paris.

J.M. Collantes et al. “Expanding the Capabilities of Pole-Zero Identification Techniques for

Stability Analysis”, IEEE Microwave Theory and Techniques International Symposium, June

2009, Boston.

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STAN Tool

Suitable for both linear and non-linear stability analysis

Very easy to use

Very easy to analyze results

Notion of “stability margin”

Oscillation mode knowledge -> Help to find the suitable

stabilization strategy

Parametric Analysis implemented

Monte-Carlo Analysis

Key Elements

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STAN Tool

Selecting the Node

Where to connect the probe for STAN analysis ?

SISO transfer function → exact

pole/zero cancellations are possible

Pole/zero cancellations are

associated with the lack of

controllability and/ or observability in

the system

real

imag

d

Pole-zero quasi-cancellation

???

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STAN Tool

Physical quasi-cancellations

in s( i ,f )outv

this node has very low sensitivity to

that dynamics (low degree of

observability and/or controllability)

When part of the circuit dynamics is electrically isolated from the node selected for the

analysis, poles representing this dynamics appear quasi-cancelled by zeroes and the effect

of this dynamics on the transfer function is very slight

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STAN Tool

In multistage Circuits

Example of a three-stage PA exhibiting an oscillation

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3-6

-4

-2

0

2

4

6

Re (GHz)

Im (

GH

z)

1_biasV _ 2biasV _3biasV

Connecting the probe to a node of the 3rd

stage, no instability is detected (we are

electrically isolated from where the actual

oscillation takes place).

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STAN Tool


Connecting the probe to a node of

the 2nd stage → physical quasi-

cancellation (we still have low

sensitivity from the observation port)

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3-6

-4

-2

0

2

4

6

Re (GHz)

Im (

GH

z)



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STAN Tool




Connecting the probe to a node of the 1st stage →

The oscillation is clearly detected, unstable poles are

not quasi-cancelled with nearby zeros (high

sensitivity). We can conclude that the origin of the

oscillation is located in the 1st stage

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3-6

-4

-2

0

2

4

6

Re (GHz)

Im (

GH

z)

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STAN Tool

Odd mode oscillation in combined amplifiers

Oscillation at f0/2 is very common in amplifiers with parallel

power combining structures

RG

f0,Pin

RL

RL

Q1

Q2

RG

f0,Pin

RL

RL

Q1

Q2

in s( i ,f )

outv

in s( i ,f )

outv

2e9

2e9

2e9

2e9

Odd mode

oscillation is not

detected at the

combining node.

Exact pole-zero

cancellation

Odd mode

oscillation is

clearly detected at

the gate of the

transistors

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STAN Tool


Po

we

r s

pli

tte

r

Po

we

r c

om

bin

er

Po

we

r

sp

litt

er

Po

we

r

sp

litt

er

RL

RG

f0 Pin

1Q

2Q

3Q

4Q

G

A

B

C

D

E

F

1st step: analysis in nodes A, B and D

A B DOscillation

type

Preferred

strategy

x x x Even mode

- x -Odd mode in

1st stage

- - xOdd mode in

2nd stageSee next slide

- - - No oscillation -

Stabilization networks can be optimized using parametric analysis -> find the best trade-off between stability and RF performances

B,C

or/ and D, E, F, G

B

C

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Po

wer

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litt

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Po

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co

mb

iner

Po

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r

sp

litt

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Po

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r

sp

litt

er

RL

RG

f0 Pin

STAN Tool


Test of the 4 branches with 4 probes, changing the phase

Odd mode oscillation

[ + - - +] or [ + - + - ]

Q1 oscillates out of

phase with Q2, same for

Q3 and Q4

Po

wer

sp

litt

er

Po

wer

co

mb

iner

Po

we

r

sp

litt

er

Po

we

r

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Po

we

r s

pli

tte

r

Po

we

r c

om

bin

er

Po

wer

sp

litt

er

Po

wer

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Po

wer

sp

litt

er

Po

wer

co

mb

iner

Po

we

r

sp

litt

er

Po

we

r

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Po

we

r s

pli

tte

r

Po

we

r c

om

bin

er

Po

wer

sp

litt

er

Po

wer

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Odd mode oscillation

[ + + - - ]

Q1 and Q2 oscillates out

of phase with Q3 and Q4

Po

wer

sp

litt

er

Po

wer

co

mb

iner

Po

wer

sp

litt

er

Po

wer

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Po

wer

sp

litt

er

Po

wer

co

mb

iner

Po

we

r

sp

litt

er

Po

we

r

sp

litt

er

RL

RG

f0 Pin

Q1

Q2

Q3

Q4

Po

we

r s

pli

tte

r

Po

we

r c

om

bin

er

Po

we

r

sp

litt

er

Po

we

r

sp

litt

er

RL

RG

f0 Pin

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STAN Tool

Performances Optimization

Example: Ku-Band MMIC PA for active space antenna

Stable original circuit

RF in RF out

RC stabilization

networks

Inter-branch

stabilization resistances

Natanael Ayllón Rozas

“Développement des méthodes de

stabilisation pour la conception des

circuits hyperfréquences : Application

à l’optimisation d’un amplificateur de

puissance spatial.”, PhD Thesis,

February 2011.

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STAN Tool



All stabilization networks removed

Parametric frequency

division /2 instability

RF in RF out

resistances maintained

for topological reasons

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STAN Tool



Optimized version

No oscillation detected,

especially around F0/2

RF in RF out

resistances maintained

for topological reasons

Stabilization

resistances

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STAN Tool


Example: Ku-Band MMIC PA for active space antennaResults comparison

OptimizedOriginal

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Thank you

www.amcad-engineering.com

Contact information:

AMCAD Engineering

20 rue Atlantis

87069 Limoges, France

Stéphane Dellier

[email protected]

+33 555 040 531 / +33 672 371 046

mailto:[email protected]