Amplifier Classes
by Manfred Thumm and Werner Wiesbeck
Forschungszentrum Karlsruhe in der Helmholtz - Gemeinschaft
Universität Karlsruhe (TH) Research University•founded 1825
Amplifier Characteristics ID mA
1200
ID
D
1000
800
UDS
G
600
U DS
UGS
400
S
200
U GS V
-5 -4 -3
-2 -1
2
Institut für Hochfrequenztechnik IHE und Elektronik
Amplifier Classes, General Characteristics ILast
I max Class-A Bias-Point Load Current Iload
I max / 2 ideal
real
Control Voltage Vcontrol
Vcontrol (normalized) -0.25
0
0.25
0.5 0.75
1
1.25
3
Institut für Hochfrequenztechnik IHE und Elektronik
Classical Amplifier Classes A, AB, B, C Iload
I max
Ideal I max / 2
Vcontrol -0.25
Class-C
0
0.25
0.5
0.75
1
1.25
Class-AB
Class-B Bias-Point
Class-A Bias-Point 4
Institut für Hochfrequenztechnik IHE und Elektronik
Amplifier Classes Conduction Angle Vcontrol
Class-A
1
Class-AB
Class-B
Class-C
0.5 0 time Conduction angle
Iload
2π
π...2π
π
0...π
IMax Imax/2 0
time
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Comparison of Amplifier Classes
Ruhestrom Bias point USteuer Relative Leistung zu Class-A Betrieb - Bei Vollaust. - Bei -3dB Anst. Mittlerer Strom - Ohne Signal - Bei Vollausst. - Bei -3dB Anst Wirkungsgrad - Bei Vollausst. - Bei -3dB Anst. Linearität Geeignet für Modulationen:
Class-A hoch 0.5
Class-AB mittel 0.25
Class-B fast Null 0
Class-C kein -0.5
0 dB - 3 dB
+0.2 dB -2 dB
0 dB - 3 dB
-0.6 dB -6 dB
0.5 Imax " "
ca. 0.25 Imax 0.37 Imax 0.3 Imax
gerade eben 0 0.3 Imax 0.2 Imax
0 0.25 Imax 0.12 Imax
78% 55% schlecht FM/PM
85% 45% extrem schlecht nur FM/PM z.B. GMSK in GSM
50% 70% 25% 52% sehr gut mittel QAM, Digitale Hochstufige Modulationen mit digitale Modulawenig Stufen tionsverfahren z.B. 8-PSK in GSM z.B. 64QAM in LTE
Ungefähre Angaben, schwanken in der Realität 6
Institut für Hochfrequenztechnik IHE und Elektronik
Harmonics Amplitudes of Amplifier Classes Fundamental (1st Harmonic)
0.5
DC from Class-B increasing of 3rd Harmonic
Amplitude Imax=1
from Cripps [1] 2nd
3rd
4th 5th
0
Conduction Angle 2π
Class-A
π
Class-AB
Class-B
0
Class-C 7
Institut für Hochfrequenztechnik IHE und Elektronik
Amplifier Classes: Filtering of Fundamental Frequency Voltage Supply (+27V)
IDrain LRF-Choke
Output Signal Drain
CDC-Block
Gate
UIn
C
R
Source
C
L
UOut
R
UGate
Negative Gate Voltage (-1...5V)
High-Q Resonance Ground Circuit at Fundamental 8
Institut für Hochfrequenztechnik IHE und Elektronik
Highly Efficient Amplifier Classes - D, E, F, S Amplifiing Element operates in Switching Mode States: Device is fully switched – Current through device is maximal but Voltage at device is zero – There is no loss power! Device is fully open – Voltage at device is maximal – but Current through device is zero – There is again no loss power! Highly Efficient Operating Mode: Classes are different by their termination (complex load) of the harmonics More complicated amplifier architectures are necessary to amplify modulations with amplitude variations Very high efficiency also for small signal operation of the amplifier (good back-off efficiency) 9
Institut für Hochfrequenztechnik IHE und Elektronik
Class-E Example
IEEE WAMI, Florida, 2004
Ideal topology
Topology with realistic Si-LDMOS
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Class-S Example - Functional Principle+
Input
Output Bandpass Delta Sigma Modulator
Switching Amplifier
Filter
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Class-S Amplifier Architecture Overview final stage switch mode amplifier
Clocking=[1.3...4] x RF carrier
Supply
Driver+Level Shifter antiphase signals Delta Sigma Modulator CT→ RFIC DT → FPGA/DSP
Reconstruction filter 1 bit
1 bit CT: RF input analogue DT: Baseband input digital
CT=Continous Time DT=Discrete Time
S
No Isolator! (directional line)
1 bit
G Noise-Shaping Filter H(z)
D
RF output (analog)
Simultaneous reconfiguration of digital and analogue filter
Switch mode - theoretical peak efficiency can reach 100% !
(78% on Class-AB) 12
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Efficiency projection for Crest factor reduced UMTS Signal
Amplifier Efficiency Roadmap We want to get here Next step
Class-S
Envelope Tracking
We are here SiC/GaN
Predistorte d Class-AB
Year
Source: Max Solondz
GaN device technology enables new architectures! 13
Institut für Hochfrequenztechnik IHE und Elektronik
Efficiency Evolution Overview for Single Band Amplifiers Today 2007
Mid Term 2008
Future 2011
>50 %
PA-Concepts + DPD (Final Stage Only!) Estimations done for single-band application. 45 %
Class-S Concept
40 %
33 %
Envelope Tracking-Concept Doherty-Concept
Class-AB
achievable performance currently under investigation!
DC Versorgung
in parallel required: enhancement and concept related optimization of linearisation algorithms
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Literature 1) Cripps Steve C, RF Power Amplifiers for Wireless Communications, Artech House, 1999, ISBN 0 89006 989 1 2) Kenington Peter B, High Linearity RF Amplifier Design, Artech House, Boston, London, 2000, ISBN 58053 143 1 3) Tri T. Ha, Solid State Microwave Amplifier Design, Krieger Publishing, Florida, 1991 4) Scott Kee, Ichiro Aoki, Ali Hajimiri, David Rutledge, The New Class E/F Family of ZVS (zero voltage) Switching Amplifiers, IEEE MTT 5) Thomas Johnson, Shawn P. Stapleton, RF Class-D Amplification With Bandpass Sigma– Delta Modulator Drive Signals, IEEE Trans. Circuit and Systems, Dec 2006
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