RF Power Amplifier Design

Transcription

1 RF Power Amplifier esign Markus Mayer & Holger Arthaber epartment of Electrical Measurements and Circuit esign Vienna University of Technology June 11, 21 Contents Basic Amplifier Concepts Class A, B, C, F, hhca Linearity Aspects Amplifier Example Enhanced Amplifier Concepts Feedback, Feedforward,... Predistortion LINC, oherty, EER,... 2

2 Efficiency efinitions rain Efficiency: = P OUT P C Power Added Efficiency: PA = P OUT P P C IN = 1 1 G 3 Ideal FET Input and Output Characteristics V GS= gm V GS=VP 2VP VP VK V max Ohmic Saturation Breakdown κ V V = V K 4

3 Maximum Output Power Match V GS= gm V GS=VP 2VP VP VK V max Ohmic Saturation Breakdown R OPT V = S max I m V K 5 Class A 2VP VP VK V max p 2p p 2p 6

4 Class A Circuit V G S RL = κ 5% G = G A (e.g.14 db) PA = κ 48% 7 Class B 2VP VP VK V max p 2p p 2p 8

5 Class C 2VP VP VK V max p 2p p 2p 9 Class B and C Circuit V f G S RL Class B = κ 78% Class C 1% G = G A - 6dB (8 db) G 1 PA = κ 65% PA % 1

6 Influence of Conduction Angle 11 Class F (HCA... harmonic controlled amplifier) 2VP VP VK V max p 2p p 2p 12

7 hhca (half sinusoidally driven HCA) 2VP VP VK V max p 2p p 2p 13 Class F and hhca Circuit V Zo(n) I Ze(n), n=even inf, n=even, n=1 inf, n=odd RL Class F = κ 1% hhca = κ 1% G = G A - 5dB (9 db) G = G A + 1dB (15 db) PA = κ 87% PA = κ 96% 14

8 hhca Third Harmonic Peaking 2VP VP VK V max p 2p p 2p 15 Third Harmonic Peaking Circuit V G S 3f f RL = κ 91% G = G A +.6dB (14.6 db) PA = κ 87% 16

9 Linearity Aspects 17 Linearity Aspects Class A Class AB Class B Class C 18

10 Linearity Aspects Ideal strongly nonlinear model Strong-weak nonlinear model 19 Amplifier esign An Example Balanced Amplifier Configuration Port 1 Z=5 Ohm Port 2 Z=5 Ohm 2

11 Amplifier esign Simulation Gate & rain Waveforms 1 Gate waveforms 1 25 rain waveforms Inner rain Voltage (L, V) Inner rain Current (R, ma) 5 Amp Amp Inner Gate Voltage (L, V) Inner Gate Current (R, ma) Amp Amp Time (ps) Time (ps) 21 Amplifier esign Simulation ynamic Load Line & Power Sweep 8 ynamic load line 4 Power Sweep 1 Tone 8 IVCurve (ma) IV_Curve Output Power (L, dbm) Amp 7 6 ynamic Load Line (ma) Amp 3 PAE (R) Amp Voltage (V) Power (dbm) 22

12 Amplifier esign Measurements Single Tone & Two Tone 4 8 PAE [%] 6 6 PAE [%] 1dB CP P out [dbm], Gain [db] P out Gain Gamma In PAE P out [dbm], IM [dbc], Gain [db] P out IM Gain PAE P in [dbm] P in [dbm] 23 Amplifier Nonlinearity Gain and Phase depends on Input Signal 3 rd Order Gain-Nonlinearities: 24

13 Amplifier Nonlinearity Higher Output Level (close to Saturation) results in more istortion/nonlinearity 25 Nonlinearity leads to? Generation of Harmonics Intermodulation istortion / Spectral Regrowth SNR (NPR) egradation Constellation eformation 26

14 Intermodulation and Harmonics 27 Spectral Regrowth relative power / db ACPR 1 >6dB ACPR 2 >6dB ACPR 1 =16dB ACPR 2 =43dB relative frequency / MHz Energy in adjacent Channels ACPR (Adjacent Channel Leakage Power Ratio) increases 28

15 Reduced NPR (Noise Power Ratio) Input Signal Output Signal of Nonlinear Amplifier egradation of Inband SNR Noisy Constellation 29 Constellation eformation Input Signal Output Signal of Nonlinear Amplifier (with Gain- and Phase-istortion) 3

16 Modeling of Nonlinearities with Memory-Effects Volterra Series (= Taylor Series with Memory ) without Memory-Effects 2 αar αθr Saleh Model f ( r) = g( r) = 2 1+ β ar 1+ βθr Taylor Series Blum and Jeruchim Model AM/AM- and AM/PM-conversion 2 better performance 31 AM/AM- and AM/PM-Conversion GaAs-PA 32

17 AM/AM- and AM/PM-Conversion LMOS-PA 33 How to preserve Linearity? Backed-Off Operation of PA Simplest Way to achieve Linearity Linearity improving Concepts Predistortion Feedforward... 34

18 How to preserve Efficiency? Efficiency improving Concepts oherty Envelope Elimination and Restoration... Linearity improving Concepts Higher Linearity at constant Efficiency Higher Efficiency at constant Linearity 35 irect (RF) Feedback Classical Method ecrease of Gain Low Efficiency Feedback needs more Bandwidth than Signal Stability Problems at high Bandwidths 36

19 istortion Feedback Feedback of outband Products only Higher Gain than RF feedback Stability Problems due to Reverse Loop 37 Feedforward Overcomes Stability Problem by forward-only Loops Critical to Gain/Phase-balances.5dB Gain Error -31dB Cancellation 2.5 Phase Error -27dB Cancellation Well suited for narrowband application 38

20 Cartesian Feedback baseband input I OPAs modulator I I main amp. local oscillator 1 RF-output UMTS example: original signal predistorted signal demodulator AM/AM- and AM/PM-correction High Feedback-Bandwidth Stability Problems relative power / db relative frequency / MHz 39 igital Predistortion igital plementation of Cartesian Feedback Additional ACs, SP Power, Oversampling needed Loop can be opened no Stability Problems 4

21 Analog Predistortion Predistorter has inverse Function of Amplifier Leads to infinite Bandwidth (!) Hard to realize (accuracy) 41 Analog Predistortion Possible Realizations: 42

22 LINC (Linear Amplification by Nonlinear Components) s(t) signal separation s(t) 1 K Ks(t) 1 K(s(t)+ 1 s(t)) 2 =Ks(t) s(t) 2 AM/AM- and AM/PM-correction igital separation required (accuracy!) High Bandwidth, oversampling necessary Stability guaranteed K Ks(t) 2 relative power / db UMTS example: s(t) s 1 (t) ACPR 1 >6dB ACPR 2 >6dB ACPR 1 =18dB ACPR 2 =29dB relative frequency / MHz 43 oherty Amplifier Auxiliary amplifier supports main amplifier during saturation PAE can be kept high over a 6dB range 44

23 oherty Amplifier Gain vs. Input Power Efficiency vs. Input Power P OUT doherty configuration (A1+A2) main amp. (A1) aux. amp. (A2) P IN No improvement of AM/AM- and AM/PM-distortion Behavior of auxiliary amplifier very hard (impossible) to realize Stability guaranteed 45 EER (Envelope Elimination and Restoration) Separating phase and magnitude information Elimination of AM/AM-distortion Application of high-efficient amplifiers (independent of amplitude distortion) Stability guaranteed amplitude information RF input signal separation phase information RF output high efficiency power amplifier 46

24 EER (Envelope Elimination and Restoration) Analog realization Limiter hard to build Accuracy problems Feedback necessary RF input peak detector supply voltage amplifier limiter RF output peak detector high efficiency power amplifier igital realization Oversampling + high /Aconversion rates required High power consumption of SP and /A-converters Possible feedback elimination Compensation of AM/PMdistortion possible digital baseband input I digital signal processor amplitude information supply voltage amplifier A A A phase information modulator I high efficiency power amplifier local oscillator RF output 47 EER (Envelope Elimination and Restoration) Bandwidth of Magnitude- and phase-signal have higher than transmit signal Five times (!) oversampling necessary to achieve standard requirements relative power / db UMTS example: Magnitude Phase relative power / db UMTS example: full bandwidth 3 B bandwidth 5 B bandwidth 7 B bandwidth ACPR 1 >6dB ACPR 2 >6dB ACPR 1 =33dB ACPR 2 =4dB ACPR 1 =51dB ACPR 2 =36dB ACPR 1 =53dB ACPR 2 =49dB relative frequency / MHz relative frequency / MHz 48

25 Adaptive Bias Varying/Switching of Bias-Voltage depending on Input Power Level Selection of Operating Point with high PAE Applicably for nearly each type of Amplifier peak detector bias control RF input RF output high efficiency power amplifier 49 Adaptive Bias power added efficiency / % Single tone PAE for switched V with V G kept constant V =3.5V V =4.5V V =6.5V output power / dbm Simply to implement Concept Stability guaranteed Possible problems: C-C converter with high efficiency necessary Possible Linearity Change (can increase and decrease) especially for HCAs 5

26 Summary igital Realization required to achieve Accuracy Problem of Stability for high Bandwidth Application Higher Bandwidths (Oversampling) necessary, depending on Order of IM cancellation Predistortion gives best Results while keeping Efficiency high (valid for high Output Levels > 4dBm) 51 Figure References F. Zavosh et al, igital Predistortion Techniques for RF Power Amplifiers with CMA Applications, Microwave Journal, Oct Peter B. Kenington, High-Linearity RF Amplifier esign, Artech House, 2 Steve C. Cripps, RF Power Amplifiers for Wireless Communications, Artech House,

27 Contact Information I Markus Mayer I Holger Arthaber markus.mayer@tuwien.ac.at holger.arthaber@tuwien.ac.at 53