Power Amplifier dynamic resistance in Envelope Tracking PA

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Politecnico

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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 Rload is mostly preferred?

Thanks a lot for any hint, in advance
Politecnico
 

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

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?
 

Politecnico said:
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?
Click to expand...
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.
 
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