introduction to memory effects
TRANSCRIPT
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INTRODUCTION TO MEMORY EFFECTS
Ahmad KhanifarPowerwave Technologies Inc.
1801 E St Andrew Place, Santa Ana, CA 92705
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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
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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.
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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.
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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.
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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:
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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
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f1 f2
v in
f2-f1 2f1-f22f2-f12f1 2f2
....55
44
33
221 +++++= inininininout vGvGvGvGvGv
IMD GENERTION MECHANISM
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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
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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.
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BASIC CIRCUIT FREQUENCY RESPONSE
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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
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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
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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!
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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
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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.
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SYSTEM CALIBRATION
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AM-AM and AM-PM RESPONSE
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AM-AM and AM-PM RESPONSE
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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.