Power Amplifier Classes Based upon Harmonic Approximation and Lumped-element Loading Networks

Transcription

1 Power Amplifier Classes Based upon Harmonic Approximation and Lumped-element Loading Networks (Invited Paper) Ramon A. Beltran, PhD. UCSD Power Amplifier Symposium September 2014 Skyworks Solutions, Inc. Proprietary Information 1

2 Power Amplifier Classes Based Upon A Finite Number of Harmonics Outline Class-A, AB, B, C, D, E and F Power Amplifiers True-transient Operation Harmonic Approximation Loading Network Topologies for Compact PAs Load-Pull Contours and Load Modulation Summary Skyworks Solutions, Inc. Proprietary Information 2

3 Ideal Power Amplifier Theory Voltage sources and switches I V Class-A Generic Power Amplifier True-transient operation Class-B Even harmonics Class-E All harmonics Class-F All harmonics Ideal Device Skyworks Solutions, Inc. Proprietary Information 3

4 Power Amplifiers Practical Issues Non-ideal voltage sources nor perfect switches Amplifier major practical issues: At high frequency Device package and technology On Resistance Intrinsic Drain Impedance And Waveform Shaping Insertion Loss Mismatching True-transient Operation is not possible Harmonic Approximation can be used Input Impedance and RF drive level Device Parasitic Non Perfect Load Impedance Operation over VSWR Skyworks Solutions, Inc. Proprietary Information 4

5 Ideal Power Amplifier Theory with Parasitics Non-Ideal voltage sources and switches V I Class-A Class-B 2 2 nd harmonic Power Amplifier with Parasitics Harmonic approximation Class-E 2 2 nd harmonic Class-F 2,3 2 nd and 3 rd harm Skyworks Solutions, Inc. Proprietary Information 5

6 Waveform Coefficients for PA Design Efficiency vs. number of harmonics Efficiency upon combination of harmonics (in %) HARM Infinite A F 2, Infinite B D, E F. H. Raab, "Maximum efficiency and output of class-f power amplifiers," IEEE Trans. Microwave Theory Tech., vol. 49, no. 6, pp , June Skyworks Solutions, Inc. Proprietary Information 6

7 Amplifier Design by Waveform Factors Coefficient values upon number of harmonics Po = γ V V eff 2 2R L I DC = γ V V DD γ I R L P DC = V DD I DC HARM γ V γ I Infinite Efficiency = P o = γ 2 Vγ I V eff P DC 2V DD 2 F. H. Raab, "Maximum efficiency and output of class-f power amplifiers," IEEE Trans. Microwave Theory Tech., vol. 49, no. 6, pp , June Skyworks Solutions, Inc. Proprietary Information 7

8 Class-A and AB PAs Transmission-lines and Lumped Elements Class-A or AB η = 50 to 60 % Z VD = R L γ V = 1 γ I = 1 It doesn t require harmonic component neither in drain voltage nor in drain current waveforms ST LDMOS FET PD57070 Efficiency: 35% in Class-A Output power: 70 Watts Frequency band: MHz Skyworks Solutions, Inc. Proprietary Information 8

9 Class-B PA implementation Transmission-lines and Lumped Elements Class-B 2 η = 70.71% Z VD = R L at f 0 = 0 at 2f 0 γ V = 1 γ I = It requires harmonic component in drain current waveforms GaN FET RF3931 Efficiency: 65%; Output power: 5 Watts; Frequency 144-MHz Skyworks Solutions, Inc. Proprietary Information 9

10 Class-C and D Transmission-lines and Lumped Elements Class-C can be regarded as a reduce conduction angle class-b with a large number of harmonic currents added at VD. Z VD = R L at f 0 = 0 at 2f 0 η = 78.5 % γ V = 1 γ I = all harmonics Class-D Class D is a push pull class-f PA -the two active devices provide each other with paths for the even harmonics. Therefore, class-d PA is related to class-f 2,3 as explain later. γ V = η = % γ I = Skyworks Solutions, Inc. Proprietary Information 10

11 Class-E True-Transient Suboptimum Operation Class-E 10 η = 100% Z VD = R L +jx L at f 0 = -j R 0 /n at nf 0 Harmonic impedances are not just short circuits. Ideal true-transient waveforms Generally mistuned at high-frequencies It is a good approximation if we have access to the intrinsic drain 2.54 GHz Skyworks Solutions, Inc. Proprietary Information 11

12 Class-E Amplifier Reactances Impedances for ideal Class-E Specific Drain Impedances Z VD Freq. f 0 Ideal Class-E R 0 =10-Ohms j f 0 -j f 0 -j f 0 -j f 0 -j f 0 -j9.03 7f 0 -j7.78 8f 0 -j6.77 9f 0 -j f 0 -j5.42 V DD = 15 V Pout = 11.5-W Z VD = (1.526+j1.106) R 0 B S =0.1836/R 0 X S =1.15 R 0 X n = -j R 0 /n Skyworks Solutions, Inc. Proprietary Information 12

13 Class-E 2 Second harmonic Approximation to Class-E Operation Class-E 2 η = 70.71% Z VD = R L +jx L at f 0 = -jx 2 at 2f 0 γ V = γ I = The 2 nd harmonic in drain current waveform requires A GIVEN REACTANCE (not just a short) ST LDMOS FET SD57030 Efficiency: 67%; Output power: 10 Watts; Frequency 900-MHz Skyworks Solutions, Inc. Proprietary Information 13

14 Class-E 2 Second harmonic Approximation to Class-E Operation Fundamental and Second harmonic Impedances V DD = 15 V Pout = 11.5-W Freq. Class-E 2 f 0 2f 0 3f 0 4f 0 5f 0 6f 0 7f 0 8f 0 9f 0 10f j8.86 -j12.28 NA NA NA NA NA NA NA NA Z VD = R 1 +jr 1 X 2 = -j1.414r 1 Second harmonic voltage and current in phase quadrature (no power dissipation) Class-E 2 drain waveforms Skyworks Solutions, Inc. Proprietary Information 14

15 Class-E Multi-harmonic Approximation Impedances for Class-E 10 Class-E 10 η = 85% Z VD = R L +jx L at f 0 = -j R 0 /n at nf 0 It requires harmonic drain currents and voltages with specific reactance values Class-E, All harmonics Class-E 10 GaN FET RF3931 Efficiency: 85%; Output power: 10 Watts; Frequency 400-MHz Skyworks Solutions, Inc. Proprietary Information 15

16 Class-E Multi-harmonic Approximation Impedances for Class-E 10 Comparison between ideal class-e and class-e 10 V DD = 15 V Pout = 11.5-W Freq. Ideal Class-E Class-E 10 Ratio E 10 /E f j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j f 0 -j j Skyworks Solutions, Inc. Proprietary Information 16

17 Class-F 2,3 Power Amplifier Second and third harmonic Class-F 2,3 η = 81.65% Z VD = R L at f 0 = 0 at 2f 0 = at 3f 0 γ V = γ I = It requires harmonic voltage and current at drain waveforms. GaN FET GP2001 PolyFET Efficiency: 81%; Output power: 17 Watts; Frequency 300-MHz Skyworks Solutions, Inc. Proprietary Information 17

18 Inverse Class-F 2,3 Power Amplifier Second and third harmonic Class-F 2,3 η = 81.65% Z VD = R L at f 0 = at 2f 0 = 0 at 3f 0 γ V = γ I = It requires harmonic voltage and current at drain waveforms. GaN FET GP2001 PolyFET Efficiency: 79%; Output power: 17 Watts; Frequency 300-MHz Skyworks Solutions, Inc. Proprietary Information 18

19 Impedances for PA classes Impedances at intrinsic drain Skyworks Solutions, Inc. Proprietary Information 19

20 Continuous Class-E 2 and F 2,3 Impedance locus Do you remember the waveform factor for class-b 2 and class-e 2 are the same? γ I = E 2 There is a transition from class-e 2 to class-b 2 PAs. 2f 0 B 2 and F B 2 F 3f 0 F Does class-j look like an specific solution case of class-e 2 PA? A harmonic load-pull for a class-e 2 PA will reveal the true. 2f 0 E 2 2f 0 F Skyworks Solutions, Inc. Proprietary Information 20

21 Power Amplifiers for RF Transmitters Enhancing efficiency at back-off Efficiency = P o P DC Maximize Po Minimize or keep same P DC ET, EER, DC-DC Po = γ V V eff 2R L 2 Doherty and Outphasing Skyworks Solutions, Inc. Proprietary Information 21

22 Using PAs in Outphasing and Doherty Load modulation for PAs H. Chireix W. Doherty Class-B PAs Measured Efficiency and/or Class-F PAs Skyworks Solutions, Inc. Proprietary Information 22

23 Load Modulation for PA classes Impedance locus for a voltage source PA Why a real amplifier does not work as expected for Outphasing or Doherty transmitters? Don t use a real PA assuming ideal load-pull contours PA 1 Outphasing PA 1 Outphasing Doherty Carrier Doherty Carrier PA 2 Outphasing However, this is not the case for a real amplifier PA 2 Outphasing Symmetric combiner Skyworks Solutions, Inc. Proprietary Information 23

24 Load Modulation for real PAs and Asymmetric Combining PAE=80% PAE=70% Po=33 dbm Chireix Asymmetric Po=30.5 dbm Doherty Asymmetric Carrier Po=28.5 dbm Doherty Carrier Asymmetric combiner Skyworks Solutions, Inc. Proprietary Information 24

25 Summary - The power amplifier efficiency depends upon the number of controlled harmonics. The harmonic impedances define the amplifier s output power capabilities and waveform shapes. Lumped-element output networks can serve for a wide frequency range. For a load modulated amplifier (i.e Doherty or Outphasing) take a look at the amplifiers load-pull contours, since they may need asymmetric combining. Not all real amplifiers can operate in either classic Doherty or Outphasing. However, DSP assisted PAs systems could overcome practical limitations by compensating phase and amplitude unbalance as well as other parameters such as linearity through predistortion. The transition between PA classes is one of the most common confusion in a real amplifier when it is tuned in the measurement bench. Skyworks Solutions, Inc. Proprietary Information 25

26 UCSD Power Amplifier Symposium September 2014 Power Amplifier Classes Based upon Harmonic Approximation and Lumpedelement Loading Networks Thank you all Questions? Skyworks Solutions, Inc. Proprietary Information 26