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Design >> RF Design >> Input matching for class E power amplifier
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Message started by uberbear on Aug 6^th, 2007, 2:16pm

Title: Input matching for class E power amplifier
Post by uberbear on Aug 6^th, 2007, 2:16pm

Hi,

I'm working on a class E power amplifier and I am wondering about the need to match the input to 50 ohms. My understanding is that if my class E power amplifier is driven by a circuit that is on the same die, then I do not need to match the input to 50 ohms. However, if I am probing my chip, then the RF cable is a transmission line and I will have to match the input to 50 ohms. I have been reading papers about class E power amplifiers and most of the time I will see an RF signal going straight to the gate of a transistor, or I will see an inductor in series with the gate capacitance, or I will see an inductor in parallel with the gate capacitance. None of these solutions match the input to 50 ohms, but all of the authors of these papers must have had an RF cable acting as a transmission line at the input when they tested their chip. How are these people able get reliable measurement results and publish a paper without matching the input to 50 ohms? Am I missing something?

Thanks in advance. This problem has been bugging me for the past month so any help would be greatly appreciated.

Title: Re: Input matching for class E power amplifier
Post by vivarf on Sep 3^rd, 2007, 7:34pm

I am also working on amplifier and my Amps are always on the same die with the previous block so I dont need to match the input to 50 Ohms. I think the inductor in series or in parallel with the gate capacitance you mentioned is exactly for matching 50 Ohms. To the best of my knowledges, for ideal input matching: there is voltage swing conversion from the source to the gate of the power amplfier (power is the same). So by calculate or measure or ... this conversion we dont have to make it match to 50 Ohms input.