INTRODUCTION TO MEMORY EFFECTS

Ahmad KhanifarPowerwave Technologies Inc.

1801 E St Andrew Place, Santa Ana, CA 92705

OUTLINE

• The sources of memory effects in an amplifier– Thermal and electrical memory effects

• The root cause• A mathematical representation of amplifier

transfer function• Circuit interactions• Dynamic non-linear characterization• Conclusions

VISIBLE IMD IMBALANCEMemory effect in an amplifier is noticed by an imbalance in the upper and lower IMD.

In many applications, the memoryeffect is masked by high 3rd orderIMD and is visible.

The memory effect in an amplifiercan be caused by thermal and electrical memory.

The thermal memory is limited tofrequencies of few hundred KHz,where as electrical memory is inthe order of few MHz to few tens Of MHz.

MODULATED MULTICARRIER SIGNAL

43 . 5 d B Of f s e tA

1RM

S W T 5 s

R F A t t 6 d B

U n it d B

R B W 3 0 k HzV B W 3 0 0 k HzR e f L v l

2 6. 5 dB mR e f L v l2 6. 5 dB m

1 2 M H z /Ce n t er 2 . 1 4 G H z S p a n 1 2 0 M H z

-90

-80

-70

-60

-50

-40

-30

-20

-10

-100

0

1

M a r k e r 1 [ T 1 ]- 4 1. 4 6 d B m

2 . 1 1 0 0 00 0 0 G H z

1 [ T 1 ] - 41 . 4 6 d B m2 . 1 1 0 0 0 0 0 0 G H z

C H P W R 3 7 . 2 0 d B mA C P U p - 0 . 0 7 d BA C P L o w 0 . 0 8 d BA L T 1 U p - 4 0 . 6 8 d BA L T 1 L o w - 4 2 . 0 6 d BA L T 2 U p - 4 3 . 3 3 d BA L T 2 L o w - 4 5 . 2 0 d B

c l 3c l 3c l 2

c l 2cl 1

c l 1C 0

C 0c u 1

c u 1c u 2

c u 2c u 3

c u 3

Frequency response a muti-Carrier amplifier response.

The predistorter correction is Limited.

Modulated signal (corrected)

4 3 . 5 d B O f f s e tA

1RM

S W T 5 s

R F A t t 6 d B

U n i t d B

R B W 3 0 k H zV B W 3 0 0 k H zR e f L v l

2 6 . 5 d B mR e f L v l2 6 . 5 d B m

1 2 M H z /C e n t e r 2 . 1 4 G H z S p a n 1 2 0 M H z

-90

-80

-70

-60

-50

-40

-30

-20

-10

-100

0

1

M a r k e r 1 [ T 1 ]- 4 4 . 9 8 d B m

2 . 1 1 0 0 0 0 0 0 G H z

1 [ T 1 ] - 4 4 . 9 8 d B m2 . 1 1 0 0 0 0 0 0 G H z

C H P W R 3 7 . 1 4 d B mA C P U p 0 . 1 1 d BA C P L o w 0 . 0 5 d BA L T 1 U p - 5 6 . 9 1 d BA L T 1 L o w - 5 5 . 3 1 d BA L T 2 U p - 5 7 . 5 8 d BA L T 2 L o w - 5 6 . 4 5 d B

c l 3c l 3c l 2

c l 2c l 1

c l 1C 0

C 0c u 1

c u 1c u 2

c u 2c u 3

c u 3

• Correction of memory effect enhances the overall correction achievable.• Memory effect can be reducedby using analogue techniques.• The memory can be correctedusing digital processing.• A hybrid approach is also Possible.

Why it is called the memory effect

2

2

1 mvEStored =

The mechanical stored energy is:

An inductor and a mechanical flywheel follow the same principle by storing energy.

2

2

1 LIEStored =

The electrical stored energy is:

ACTIVE DEVICE TRANSER FUNCTION

I n p u tM a t c h i n g

C i r c u i t

O u p u tM a t c h i n g

C i r c u i t

B a i sC i r c u i t

C g s g 1 v i n g 2 v 2i n g 3 v 3

i ng n v n

i n

R S

R L

22

22

33

221

33

221

),(

dsmdgsdmdsgsmd

dsddsddsd

gsmgsmgsmdsgsds

vgvgvvg

vgvgvg

vgvgvgvvi

++⋅⋅

+++

+++=

IEEE Trans on MTT, Vol.42, No.1, Jan. 1994

f1 f2

v in

f2-f1 2f1-f22f2-f12f1 2f2

....55

44

33

221 +++++= inininininout vGvGvGvGvGv

IMD GENERTION MECHANISM

2nd order(Harmonic)

2nd Order(Envelope)

3rd order(Transconductance)

Visible IM

Re (IM3L)

Img(

IM3L

)

A vectorial representation of IMD suggests that the majorcontributors are:• 3rd order nonlinearity (trans- conductance)• 3rd order terms generated by 2rd harmonic• 3rd order terms generated by the envelope of the signal

A VECTORIAL REPRESENTATION OF IMD

PRACTICAL IMPLEMENTATION

Most RF Power devices require a relatively wide printed circuit traceto deliver the appropriate current to the circuit.

Such a trace has a relatively Small inductance per unit length but thiscan easily disturb the outputmatching network.

RF capacitors are needed to provideLarge impedance at the fundamentalfrequency of operation.

BASIC CIRCUIT FREQUENCY RESPONSE

BIAS CIRCUIT DESIGN (classic approach)

λ/4

RF

and

video

sho

rtcircu

it

Ou

tpu

t Match

ing

Circu

itA

ctive device

D r a i n

G a t e

ZDDZBB

Input Matching Network

OutputMatching Network

TRL

TRL

BIAS CIRCUIT DESIGN (classic approach Cont.)

Reso

nace circu

it

Ou

tpu

t Match

ing

Circu

itA

ctive device

D r a i n

G a t e

ZDDZBB

Input Matching Network

OutputMatching Network

TRL

20 40 60 800 100

0.020.040.060.080.100.120.140.160.18

0.00

0.20

freq, MHz

mag(Zin1)

RR1R=50 Ohm

CAPP2C1

Exp=2.0FreqRes=12.0 MHzFreqQ=12.0 MHzQ=26.0TanD=0.038C=1.0 uF

CAPP2C2

Exp=2.0FreqRes=20.0 MHzFreqQ=20.0 MHzQ=26.0TanD=0.038C=0.1 uF

SP_NWASP_NWA1

+ +

21

A PRACTICAL NOTE

There are pros and cons on the Introduction of transmission zerosin frequency response of video decoupling network!

FREQUENCY SYNTHESIS

Vs

S R C 1C 4C 1

L s2

L s3

C 6C 7

L8

L7

L1

L6

C 5 L5

R s rs

L4

R 1

Ls

1 . 0 E 7 2 . 0 E 7 3 . 0 E 7 4 . 0 E 70 . 0 5 . 0 E 7

0 . 0 3

0 . 0 4

0 . 0 5

0 . 0 6

0 . 0 7

0 . 0 2

0 . 0 8

mag(Z

s)

F r e q , M H z

1 . 0 E 7 2 . 0 E 7 3 . 0 E 7 4 . 0 E 70 . 0 5 . 0 E 7

0

2 0

4 0

6 0

8 0

- 2 0

1 0 0

F r e q , M H z

phase

(Zs)

It is possible to design a predefined video response For the gate and drain RF decoupling network

MEASUREMENT OF DYNAMIC

CHARACTERISTICS

Amplifierundertest

power supplyVDD

power supplyVGG

Temperature controlled fans

tempprobe

PowerMeter ch B

Peak PowerMeter

power supply

PowerMeter chA

Atte

nuator

RF Vector SignalAnalyzer

10 MHztiming sink

10BaseTethernetswitch

RF Vector SignalGenerator

Pre-amp

10 MHztiming source

Attenuator

The dynamic characteristicsof an amplifier response by sampling the the output @ anappropriate rate.

SYSTEM CALIBRATION

AM-AM and AM-PM RESPONSE

AM-AM and AM-PM RESPONSE

CONCLUSIONS

• The electrical memory effect is a by-product of the interaction between active device nonlinearity and DC decoupling at the gate (base) and drain (collector) terminals.

• The 2nd harmonic impedance also contribute to the memory effects observed in an amplifier

• Analogue circuit techniques can be used to reduce the memory effects

• The thermal memory is best corrected by digital means and adequate thermal management.