1. Class D Power amplifier -----using ADS
Song June30

2. Outline Why select Class D? Compare different device
Simple Class D architecture
Load-pull to give out Zout
Matching and simulation results of ideal narrow band Class D PA
Broad band matching

3. Why Class D?
Class D PA works in the switching mode, with a square wave voltage and a half wave rectified sine wave of current.
In its ideal switching mode,
when Vds<>0, Ids=0;
when Ids<>0,Vds=0.
Class D PA can achieve very high frequency close to 100%. Although it is very nonlinear, we still can use the LINC technique to kill the IMD product.

4. Two kinds of Class D PA

5. Compare the device(I) For high frequency, ----- the higher the better
For high on/off switching speed, the shorter the better
For high efficiency, the on-resistance of a switching device must be as low as possible to minimize the power dissipation in the switches during the positive half cycle Rs is the smaller the better.
For high Power output, BV(beake down voltage)
the higher the better
For high Gain, the bigger the better
For power dissipate, the small the better

6. Compare the device(II)
Conclusion:
Also for the wide band application, we should chose the component whose Zout and Zin has very little variety in some frequency range.
I suggest to use the MRF282SR N-channel Enhancement-Mode Lateral MOSFETs

7. Basic Class D PA architecture

8. Load Pull to give out Zout

9. Narrow band input and output matching and simulation results

10. Wide band matching using coaxial
A conventional design allows the coaxial transformer to transform the impedance to obtain a match the low end of the band, then add additional low-pass matching sections to lower the impedance at the upper band edge.

11. Using the MRF282S to simulate narrow band VMCD @300MHz

12. Push_pull structure

13. Narrow band matching (input, output)

14. Narrow band simulation results

15. Final schematic

16. Final simulation results(1)

17. Final simulation results(2)

18. The problem remain:
The Class D PA need a resonator tank to pull out the fundamental signal, to filter out the third time signal, so I decide to divide the band into 3 parts, one from 30 to 88 MHz; 88MHz to 200MHz; 200MHz to 500MHz. We can separate the signals by filter bank.
For the real device, the Rs isn’t very small, so the efficiency can’t be so high. Because of the , the Vds and some overlap with Ids, it also kill some efficiency.
To achieve better performance at low frequency band, I have to increase the Vgg.
ADS is very hard to converge when simulation.

19. Thank you!!!