Power Amplifier dynamic resistance in Envelope Tracking PA

[Politecnico]

Hi All

The primary simulation of Envelope Modulator (for Envelope Tracking Power Amplifier) is always done with a fixed resistor as the dynamic resistance of PA and it's normally around 5-10 Ohm.

1) How may I find that approximate resistance to be assumed as the load of the Envelope Modulator? Is there any calculation, measurement, ...?

2) Why lower R_load is mostly preferred?

Thanks a lot for any hint, in advance
Politecnico

 

[D.A.(Tony)Stewart]

Look,at VI curve of PA and load of same ESR will produce 50% modulation. Any modulation index can be used by R ratios.

 

[Politecnico]

Look,at VI curve of PA and load of same ESR will produce 50% modulation. Any modulation index can be used by R ratios.

Actually, I read somewhere that we can divide Vdd by Idd (drain's DC current consumption) at PA's compression point. Is that a valid statement?

 

[mtwieg]

Actually, I read somewhere that we can divide Vdd by Idd (drain's DC current consumption) at PA's compression point. Is that a valid statement?

No, when biased near compression, Vdd/Idd should be quite nonlinear. At the very least, you want a load impedance equal to the slope resistance, which is not Vdd/Idd. A good simulation should use a nonlinear load derived from measurements of the PA under many operating conditions.