Download - Comm d Runt on Pa Symposium 11
-
7/30/2019 Comm d Runt on Pa Symposium 11
1/37
Doherty Power Amplifier DesignDavid W. Runton, Michael D. LeFevre, Matthew K. Mellor
RFMD, Chandler, AZ, [email protected]
-
7/30/2019 Comm d Runt on Pa Symposium 11
2/37
Introduction
Intentions
With high peak to average ratio signals in full use in the
commercial world and expanding in the military world, how do
we efficiently amplify these signals?
Doherty is old news!
PA suppliers are getting very nearly equal results
Optimizations/tweaks are simply exploiting tradeoffs
How do we put it all together?
And most importantly, do it quickly
Page 2
-
7/30/2019 Comm d Runt on Pa Symposium 11
3/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 3
-
7/30/2019 Comm d Runt on Pa Symposium 11
4/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 4
-
7/30/2019 Comm d Runt on Pa Symposium 11
5/37
The Traditional Balanced Amplifier
Both amplifier A1 and A2 contribute equally to Pout
Both have standard Efficiency vs. Pout characteristics
A2
A1
Pout
h
,DrainEfficien
cy
Page 5
-
7/30/2019 Comm d Runt on Pa Symposium 11
6/37
The Doherty Amplifier
A1 operates most of the time - handles average signal
A2 operates only when peak power is needed
A1 and A2s operation is dependent on each other
Pout
h,
DrainEfficiency
A1
A2
Ideal - A1 + A2Carrier Amp
Peaking Amp
Page 6
-
7/30/2019 Comm d Runt on Pa Symposium 11
7/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 7
-
7/30/2019 Comm d Runt on Pa Symposium 11
8/37
Operational Fundamentals Class A
Page 8
0 90 180 270 360 450 540 630 7200
0.5
1
1.5
2
2.5Waveforms
Voltage
Zero knee Current
Vknee = 0 Ibias = 0.5
VDC = 1.0 Isignal = 0.5
Vsignal(fund) = 1.0
Under basic loadline condition
*Reference [1]
= cos()
= cos( + )
-
7/30/2019 Comm d Runt on Pa Symposium 11
9/37
Operational Fundamentals Class B
Page 9
0 90 180 270 360 450 540 630 7200
0.5
1
1.5
2
2.5Waveforms
Voltage
Zero knee Current Load Resistor RLAdjust Input Drive for Max V
Vknee = 0 Ibias = 0
VDC = 1.0 Isignal = 1.0
Vsignal(fund) = 1.0
= 0 + 1 cos()
+ cos(2)
+ cos 3 +
= 1 cos()
The output waveforms must be
expanded into its Fourier series
components
Vds is simplified due to shortcircuited harmonics
*Reference [1]
-
7/30/2019 Comm d Runt on Pa Symposium 11
10/37
Operational Fundamentals Class B at half power
Page 10
Vknee = 0
VDC = 1
Ibias = 0
0 90 180 270 360 450 540 630 7200
0.5
1
1.5
2
2.5Waveforms
Voltage
Zero knee Current
Drive Signal -6dB
Efficiency Drops by 2*Reference [2]
-
7/30/2019 Comm d Runt on Pa Symposium 11
11/37
Operational Fundamentals Class B (Load Modulation)
Page 11
Vknee = 0
VDC = 1
Ibias = 0
0 90 180 270 360 450 540 630 7200
0.5
1
1.5
2
2.5Waveforms
Voltage
Zero knee Current
RL2xRLEfficiency Restored
*Reference [2]
-
7/30/2019 Comm d Runt on Pa Symposium 11
12/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 12
-
7/30/2019 Comm d Runt on Pa Symposium 11
13/37
Textbook Load Modulation
Doherty achieves Load
modulation by using the
principle of load pulling
using two devices*RLV
I1 I2
1
2
11
I
IRZ
L
Page 13
*Reference [3]
+
-+
-
-
7/30/2019 Comm d Runt on Pa Symposium 11
14/37
Textbook Load Modulation
LRZZ 221
RL+-
+-V
I1 I2
RL+
- V
I1
02 I
LRZ 1
Case I
Both amplifiers contributing equally
Case II
Peaking amp off
Page 14
*Reference [3]
-
7/30/2019 Comm d Runt on Pa Symposium 11
15/37
Car
Pk
4,
lengthZZ ODoherty
Carrier
Peaking Carrier
Peaking
4
length
4,2
length
Z
ZO
xfmr
Create a splitter
Wilkinson
Gysel
Hybrid
Doherty Topology Definitions
Page 15
-
7/30/2019 Comm d Runt on Pa Symposium 11
16/37
The real implementation modulates Zo2xZo At the current source plane we want RL2xRL
How do we get this?
2xZO
2
OZ
Car
4,
lengthZZ ODoherty
Carrier
In package/PCB
Match
2xRL
Practical Circuit Load Modulation
+
-
I
High Power Low Power
Page 16
-
7/30/2019 Comm d Runt on Pa Symposium 11
17/37
At the combiner node, we want Zpk = When the peaking amp is off
An additional phase shift can create this,
2
OZ
Car
4,
lengthZZ ODoherty
Carrier
Peaking
Pk
ZPeaking
Includes: In package
and PCB Match
Designing the Doherty Peaking off state
Page 17
-
7/30/2019 Comm d Runt on Pa Symposium 11
18/37
DohertyThe Key to Operation or Why Doesnt it Work?
Page 18
0 VinVin
2
Imax
2
Imax
4
DeviceCurrent
Input Drive
0
Vmax
Vmax
2
DeviceVoltage
Input Drive
VinVin
2
No Clipping Allowed
*Reference [3]
-
7/30/2019 Comm d Runt on Pa Symposium 11
19/37
Doherty Topologies
There is no differentiation between standard and inverted
Doherty topologies
The Point of a Doherty amplifier is load modulation
how you achieve target impedances is irrelevant
Page 19
-
7/30/2019 Comm d Runt on Pa Symposium 11
20/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 20
-
7/30/2019 Comm d Runt on Pa Symposium 11
21/37
GaN Device used for Design Example
RF IN
VGQ
Pin 1 (CUT)
RF OUT
VDQ
Pin 2
GND
BASE
Features
Advanced GaN HEMT Technology
Peak Modulated Power > 240W
Single Circuit for 865
960MHz 48V Operation Typical Performance
o Pout 47dBm
o Gain 20dB
o Drain Efficiency 39%
o ACP -31.5dBc
o Linearizable to -55dBc with DPD
Optimized for video bandwidth and minimized
memory effects
RF tested for 3GPP performance
RF tested for peak power using IS95
Large signal models available
Page 21
-
7/30/2019 Comm d Runt on Pa Symposium 11
22/37
Being Statistically Realistic
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 00.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Doherty Efficiency, CW Case
Backoff (dB)
Efficiency(%)
1:1
1:1.51:2
1:2.5
-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 00.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Doherty Efficiency, Modulated Case 7.5dB PAR
Backoff (dB)
Efficiency(%)
1:1
1:1.5
1:2
1:2.5
CHALLENGE: Design a symmetric Doherty Amplifier foradBmaverage power operation with pdB peak to average ratio
Page 22
-
7/30/2019 Comm d Runt on Pa Symposium 11
23/37
Choosing the Load Conditions
CHALLENGE: Design a symmetric Doherty Amplifier foradBmaverage power operation with pdB peak to average ratio
To achieve the best efficiency, we need:
Pout = apdBm composite power (full peak power)
Full contribution of peak power from each amplifier
Pout = (ap-6)dBm
Carrier amplifier is fully saturated
Peaking amplifier is just about to turn on
(ap-6)dBm > Pout > (ap)dBm Carrier amplifier maintains saturation without clipping
Peaking amplifier is load modulating the carrier amplifier
Page 23
-
7/30/2019 Comm d Runt on Pa Symposium 11
24/37
Choosing the Load Conditions
CHALLENGE: Design a symmetric Doherty Amplifier foradBmaverage power operation with pdB peak to average ratio
Break the challenge into two static cases
At adBm composite power
Each amplifier is functioning at (a-3)dBm
Full addition of power from carrier and peaking amp recreating all peaks
Amplifier must not clip
At slightly < adBm composite power
Ifp is 6dB Carrier amplifier is functioning < adBm and is fully saturated (high efficiency)
If the peaking amplifier is off, this represents the best case efficiency
Be careful ifpis 6dB (for the symmetric case)
Page 24
-
7/30/2019 Comm d Runt on Pa Symposium 11
25/37
Car
Pk
Composite PoweradBmPower from each amp (a-3)dBm
Choosing the Load Conditions
Page 25
-
7/30/2019 Comm d Runt on Pa Symposium 11
26/37
5
5
6
6
6
7
719.2
19.6
19.6
20
20
20
20.4
20.4
20.4
20.8
20.8
20.8
32
36
36
40
40
40
44
44
44
48
48
(Z0ld1
)
(Z0ld1
)
4 6 8 10 12 14 16 18 20 22
2
4
6
8
10
12
14
16
PAR (prpl 6.6)()()
Gt_dB (prpl 20.3)()()Drain_eff (prpl 39.4)()()
Data Point (prpl 11.7+j6.9)()()
Load Contours: (a-3)dBm
Page 26
-
7/30/2019 Comm d Runt on Pa Symposium 11
27/37
Car
Pk
Power from Carrier amp: adBm
Page 27
-
7/30/2019 Comm d Runt on Pa Symposium 11
28/37
3
4
4
4
55
18.4
18.8
19.2
19.2
19.2
19.2
19.6
19
.6
19.6
19.6
20
20
20
44
44
48
48
52
52
52
56
56
56
60
(Z0ld1
)
(Z0ld1
)
6 8 10 12 14 16
4
6
8
10
12
14
16
PAR (prpl 4.9)(blk 4.2)()
Gt_dB (prpl 19.8)(blk 20.0)()
Drain_eff (prpl 50.8)(blk 55.4)()
Data Point (prpl 11.7+j6.9)(blk 12.6+j10.0)()
Load Contours: adBm
Page 28
-
7/30/2019 Comm d Runt on Pa Symposium 11
29/37
Doherty Design - Outline
Concept Introductions
Operational Fundamentals
The Functional Doherty Design Load Modulation
Empirical Doherty Design Example
Building the Doherty Amplifier
1
2
3
4
5
Page 29
-
7/30/2019 Comm d Runt on Pa Symposium 11
30/37
Static Tuning Reality sets in
Model the circuit
Tune under static conditions
Assume load modulation
ZO
Pkg/wires PCB Doherty xfmrCarrier
Pkg/wires PCB Doherty xfmrCarrier
2
OZ
ZHigh Power
2xZO
ZLow Power
a-3dBm
adBm
Page 30
-
7/30/2019 Comm d Runt on Pa Symposium 11
31/37
The Carrier Amp is where it all happens! We want no Clipping at full power with Zo impedance
Saturation with peaking amplifier off
Must make assumptions about peaking amp and its ability to load modulate
Car
Pk
Carrier
Tuning Tips Carrier Amp
Car
Pk
Carrier
Option 1 Peaking Amp in place Option 2 Peaking Amp removed
Page 31
-
7/30/2019 Comm d Runt on Pa Symposium 11
32/37
Car
Pk
Carrier
Peaking Carrier
Peaking
Tuning Tips Peaking Amp
Set the off-state Z of peaking amp with
Is this really so important
Can we find some advantage not to set the off-state to ideal?
Conventional wisdom says equal phase in each
branch
Class-C peaking amp has large AM-PM component
Where do we want phase alignment?
Peaking
Page 32
-
7/30/2019 Comm d Runt on Pa Symposium 11
33/37
50% Drain Efficiency
(7.5dB PAR @ 0.01% CCDF)
Fully Linearizable with peak power recovery
15% bandwidth
Tuning Tips Putting it all together
Page 33
-
7/30/2019 Comm d Runt on Pa Symposium 11
34/37
Broadband Performance and Reality
Performance is only as good as your load modulation bandwidth
Page 34
-
7/30/2019 Comm d Runt on Pa Symposium 11
35/37
Summary
The Doherty Amplifier topology can provide efficiency
benefits
Implementation is full of pitfalls
Variants are many, based on the same concept
Page 35
-
7/30/2019 Comm d Runt on Pa Symposium 11
36/37
Do You Have
Any Questions?
Page 36
-
7/30/2019 Comm d Runt on Pa Symposium 11
37/37
References
[1] Colantonio, Giannini, Limiti, High Eff ic iency RF and Microwave Sol id State
Power Am pl i f iers, Wiley and Sons, 1999, p 49-82
[2] Cripps, S., Doherty RF Power Amplifiers, Theory and Practice, Shor t
Cou rse SC-4, 2009 International Microwave Symposium, Boston
[3] Cripps, S., RF Power Ampl i f iers for Wireless Communicat ions, Artech
House, 1999, p 225-235