ZVxPlus Application: Power Amplifier Design
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This document discusses power amplifier design and summarizes key concepts: - It describes figures of merit like efficiency and power added efficiency. - It explains the concept of load lines and how to tune the source and load using load pull and source pull. - It discusses different classes of amplifier operation (A, AB, B) and their drain current and voltage waveforms. - It demonstrates how to design for each class using the ZVxPlus tool, which allows active harmonic tuning to optimize the load.
ZVxPlus Application: Power Amplifier Design
- 1. ZVxPlus Application PA Design April 2009
- 2. Introduction ● The power amplifier ● Figures of merit ● Concept of load line ● Tuning in Practice: Source and load pull ● Classes of operations ● Conclusion © Copyright 2009 2
- 3. The power amplifier PDC conversion of DC power, PDC into RF power, P o) P(f o at fo minimal input power P(f P o) o P(f P o) i non-linear P(f ≠fo) o to control conversion P diss © Copyright 2009 3
- 4. Figure of merit ● Efficiency: quality factor for DC consumption P(fo) o η= D P(fo)+P i DC ● Power Added Efficiency (PAE): ratio between the RF power 'added' by the amplifier and the DC power required for this addition. P-P o i D PAE= PDC linearity: Class A: excellent η: Class A: 50% Class AB: between A and B Class AB: between A and B Class B: moderate Class B: 78.5% Class C: poor Class C: >78.5% © Copyright 2009 4
- 5. Concept of load line ID DC IV Curve D VMax - VKnee I Max VGG1 RL= I Max D VGG2 I DD LOADLINE D VGG2 VGG VDD VD D D D VKnee VDD VMax bias point ZL=RL i drain RL vin vdrain i © Copyright 2009 5
- 6. Classic Source / load pull VGG VDD Power oriented Optimal load @ f0 power meter load tuner vdrain source vin tuner spectrum analyser © Copyright 2009 6
- 7. Source / load pull with the ZVxPlus VDD Active injection Optimal load @ 2f0 @ f0 Optimal input DUT idrain match load 50Ω tuner source vdrain tuner VSG VGG (control amplitude and phase) a1 b1 b2 a2 No power meter needed This can be done using the ZVxPlus No spectrum analyser needed and we get the waveforms for free © Copyright 2009 7
- 8. Classes of operation ● Classes of operations ● Class A ● Class AB ● Class B → Loadline? → Drain current and drain voltage waveforms? © Copyright 2009 8
- 9. Classes of operation: Class A ID ID D theoretical D I Max =50% if V Knee=0V I Max V DD D I Max RL= 0.5 I Max 2 A D 2 V −V Knee with V DD≈ Max V Knee 2 VD VG D D D VKnee VDD VMax Vdrain D Idrain D VMax I Max D D t t © Copyright 2009 9
- 10. Fundamental load tuning Vg Vd Port 3 Excitation a3 Source a1 b1 b2 a2 Synchroniser Synchroniser 20 dB 20 dB Port 1 Optimal load @ f0 50Ω © Copyright 2009 10
- 11. Class A in practice: Overrange © Copyright 2009 11
- 12. Overrange Solution Adding a characterised 6dB attenuator in a2 channel on the fly! Vg Vd Port 3 Excitation a3 Source a1 b1 b2 a2 Synchroniser Synchroniser 20 dB 20 dB Port 1 Optimal load 6 dB @ f0 50Ω © Copyright 2009 12
- 13. Class A in practice © Copyright 2009 13
- 14. Classes of operation: From Class A to AB, the first step ID ID D D I Max D I Max A D 2 AB Change bias point VD VG D D D VKnee VDD VMax Vdrain Clipping!! D Idrain D VMax I Max D D t t The drain voltage contains harmonics → goal is a sine wave drain voltage © Copyright 2009 14
- 15. Class AB, first step in Practice © Copyright 2009 15
- 16. Harmonic output termination: tuned load VGG VDD ZL=RL @ fo ZL=0 @ 2fo, 3fo , ... i 1,i 2, ...,i3 i drain vin vdrain i1 In case of : - a perfect harmonic short - maximum voltage swing of 2VDD - no knee region VDD the optimum value of load resistance will be: RL= D I @f o © Copyright 2009 16
- 17. Classes of operation: Class AB theoretical ID D I Max η >50% and < 78.5% D A A AB AB VD VG D D D due to: - termination at harmonics Vdrain Idrain - increased input signal D No clipping!! D D - shift of V VMax I Max D D t α/2 t © Copyright 2009 17
- 18. Harmonic active tuning Vg Vd Port 3 Excitation a3 Source a1 b1 b2 a2 Synchroniser Synchroniser Active injection Port 1 20 dB 20 dB Optimal load @ 2f0 20 dB @ f0 50Ω VSG (control amplitude and phase) © Copyright 2009 18
- 19. Class AB in practice © Copyright 2009 19
- 20. Classes of operation: Class B DD theoretical ID D I Max η=78.5% D A AB B A AB B VD VG D D D Vdrain Idrain D VMax I Max D D t α/2 t Note: in case of a perfect short at all harmonics © Copyright 2009 20
- 21. ... to Class B © Copyright 2009 21
- 22. Conclusion ● Fast Power Amplifier Design using ZVxPlus has been demonstrated. ● Using the ZVxPlus, a RF Design engineer can do on the fly a concrete application design, with one single tool. This tool gives all the information needed for the design. It will surely open new domains and applications. For more information info@nmdg.be www.nmdg.be © Copyright 2009 22