Introduction to Memory Effects: The sources of Memory Effects in Power Amplifiers. What the root cause is and a mathematical representation of amplifier transfer function. More: Circuit Interactions, Dynamic Non-Linear Characterization and conclusions. See more at linamptech.com

1. INTRODUCTION TO
MEMORY EFFECTS
Ahmad Khanifar
Powerwave Technologies Inc.
1801 E St Andrew Place, Santa Ana, CA 92705

2. 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

3. VISIBLE IMD IMBALANCE
Memory effect in an amplifier is
noticed by an imbalance in the
upper and lower IMD.
In many applications, the memory
effect is masked by high 3rd order
IMD and is visible.
The memory effect in an amplifier
can be caused by thermal and
electrical memory.
The thermal memory is limited to
frequencies of few hundred KHz,
where as electrical memory is in
the order of few MHz to few tens
Of MHz.

4. MODULATED MULTICARRIER SIGNAL
M a r k e r 1 [ T 1 ]
4 3 . 5 d B O f f s e t
A
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 z
R e f L v l
V B W 3 0 0 k H z
2 6 . 5 d B m
c l 3
c l 2
c l 1
c u 1
c u 2
c u 3
C e n t e r 2 . 1 4 G H z 1 2 M H z / S p a n 1 2 0 M H z
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
1
- 4 1 . 4 6 d B m
2 . 1 1 0 0 0 0 0 0 G H z
1 [ T 1 ] - 4 1 . 4 6 d B m
2 . 1 1 0 0 0 0 0 0 G H z
C H P W R 3 7 . 2 0 d B m
A C P U p - 0 . 0 7 d B
A C P L o w 0 . 0 8 d B
A L T 1 U p - 4 0 . 6 8 d B
A L T 1 L o w - 4 2 . 0 6 d B
A L T 2 U p - 4 3 . 3 3 d B
A L T 2 L o w - 4 5 . 2 0 d B
c l 3
c l 2
c l 1
C 0
C 0
c u 1
c u 2
c u 3
Frequency response a muti-
Carrier amplifier response.
The predistorter correction is
Limited.

5. Modulated signal (corrected)
M a r k e r 1 [ T 1 ]
4 3 . 5 d B O f f s e t
A
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 z
R e f L v l
V B W 3 0 0 k H z
2 6 . 5 d B m
c l 3
c l 2
c l 1
c u 1
c u 2
c u 3
C e n t e r 2 . 1 4 G H z 1 2 M H z / S p a n 1 2 0 M H z
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
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 m
2 . 1 1 0 0 0 0 0 0 G H z
C H P W R 3 7 . 1 4 d B m
A C P U p 0 . 1 1 d B
A C P L o w 0 . 0 5 d B
A L T 1 U p - 5 6 . 9 1 d B
A L T 1 L o w - 5 5 . 3 1 d B
A L T 2 U p - 5 7 . 5 8 d B
A L T 2 L o w - 5 6 . 4 5 d B
c l 3
c l 2
c l 1
C 0
C 0
c u 1
c u 2
c u 3
• Correction of memory effect
enhances the overall correction
achievable.
• Memory effect can be reduced
by using analogue techniques.
• The memory can be corrected
using digital processing.
• A hybrid approach is also
Possible.

6. Why it is called the memory effect
An inductor and a mechanical flywheel follow the
same principle by storing energy.
The mechanical
stored energy is:
2
E 1 mv Stored =
2
The electrical
stored energy is:
2
E 1 LI Stored =
2

7. ACTIVE DEVICE TRANSER FUNCTION
I n p u t
M a t c h in g
C ir c u it
O u p u t
M a t c h in g
C ir c u it
B a i s
C i r c u i t
C g s g 1 v i n g 2 v 2
i n g 3 v 3
i n
g n v n
in
R S
R L
2
i v v g v g v g v
= + + +
g v g v g v
+ + +
g v v g v g v
2
ds gs ds m gs m gs m gs
d ds d ds d ds
2
× × + +
2
3
3
2
1 2
3
3
2
1 2
( , )
md gs ds m d gs md ds
IEEE Trans on MTT, Vol.42, No.1, Jan. 1994

8. IMD GENERTION MECHANISM
f1 f2
v in
1 2 = + + + + + out in in in in in v G v G v G v G v G v
5 ....
5
4
4
3
3
2
f2-f1 2f2-f1 2f1-f2 2f1 2f2

9. A VECTORIAL REPRESENTATION OF IMD
2nd order
(Harmonic)
2nd Order
(Envelope)
3rd order
(Transconductance)
Visible IM
Re (IM3L)
Img(IM3L) A vectorial representation
of IMD suggests that the major
contributors are:
• 3rd order nonlinearity (trans-conductance)
• 3rd order terms generated
by 2rd harmonic
• 3rd order terms generated
by the envelope of the signal

10. PRACTICAL IMPLEMENTATION
Most RF Power devices require a
relatively wide printed circuit trace
to deliver the appropriate current
to the circuit.
Such a trace has a relatively Small
inductance per unit length but this
can easily disturb the output
matching network.
RF capacitors are needed to provide
Large impedance at the fundamental
frequency of operation.

11. BASIC CIRCUIT FREQUENCY
RESPONSE

12. BIAS CIRCUIT DESIGN
(classic approach)
l/4
RF and video short
G a t e
circuit
Active device Circuit
Output Matching
D r a i n
ZBB ZDD
Input
Matching
Network
Output
Matching
Network
TRL
TRL

13. BIAS CIRCUIT DESIGN
(classic approach Cont.)
Resonace circuit
Active device Circuit
Output Matching
G a t e
D r a i n
ZBB ZDD
Input
Matching
Network
Output
Matching
Network
TRL

14. A PRACTICAL NOTE
0 20 40 60 80 100
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
freq, MHz
mag(Zin1)
R R1
R=50 Ohm
CAPP2
C1
C=1.0 uF
1 2
+ +
TanD=0.038
Q=26.0
FreqQ=12.0 MHz
FreqRes=12.0 MHz
Exp=2.0
CAPP2
C2
C=0.1 uF
TanD=0.038
Q=26.0
FreqQ=20.0 MHz
FreqRes=20.0 MHz
Exp=2.0
SP_NWA
SP_NWA1
There are pros and cons on the
Introduction of transmission zeros
in frequency response of video
decoupling network!

15. FREQUENCY SYNTHESIS
V
s
S R C 1
C 1 C 4
L s
2
L s
3
C 7 C 6
L8
L7
C 5 L
L1
L6
5
R s r
s
L4
R 1
L
s
0 . 0 1 . 0 E 7 2 . 0 E 7 3 . 0 E 7 4 . 0 E 7 5 . 0 E 7
0 . 0 8
0 . 0 7
0 . 0 6
0 . 0 5
0 . 0 4
0 . 0 3
0 . 0 2
mag(Zs)
F r e q , M H z
0 . 0 1 . 0 E 7 2 . 0 E 7 3 . 0 E 7 4 . 0 E 7 5 . 0 E 7
1 0 0
8 0
6 0
4 0
2 0
0
- 2 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

16. MEASUREMENT OF DYNAMIC
CHARACTERISTICS
power supply
Amplifier
under
test
VDD
power supply
VGG
Temperature controlled fans
temp
probe
Power
Meter ch B
10BaseT
ethernet
switch
Peak Power
Meter
10 MHz
timing source
power supply
Power
Meter chA
Attenuator
RF Vector Signal
Analyzer
10 MHz
timing sink
RF Vector Signal
Generator
Pre-amp
Attenuator
The dynamic characteristics
of an amplifier response by
sampling the the output @ an
appropriate rate.

17. SYSTEM CALIBRATION

18. AM-AM and AM-PM RESPONSE

19. AM-AM and AM-PM RESPONSE

20. 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.