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Phase distortion in PAs?

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3 years 4 months ago #271 by Dave
Dave created the topic: Phase distortion in PAs?
Does anyone know of a good reference that deals with phase distortion in PAs? Specifically, is it possible to predict reliably how much the phase is going to change as it moves from the linear/small signal region into saturation?

Thanks

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3 years 4 months ago - 3 years 4 months ago #272 by madengr
madengr replied the topic: Phase distortion in PAs?
Steve Cripps has a few pages on AM-PM in his fist PA book, but says, paraphrased, "the only way to treat it in a concise manner are functions fitted physical to measurements". It's primarily from the bias dependent gate-source and drain-source caps, and gate resistance, which make it dependent on source and load match. From his example for class A, the AM-PM only starts past P1dB, but climbs sharply at 3 dB into compression, up to 25 degrees at 4 dB into compression. Then, the deeper into class AB, it shows AM-PM in the smaller signal region; it starts several dB before P1dB.

Peter Kennington's "High Linearity RF Amp Design" also shows about the same for class A; doesn't do much, about 1 degree until P1dB. He also shows it for class C, and it's about 10 degree shift over a 20 dB change in drive power, but that also shows about a 7 dB gain expansion in that range.

I suppose a rule of thumb is that you can ignore it if there is no gain expansion or compression in the range you are operating, but that's just an ass-umption.

After paging through several of my books, they all seem to be measurement based. I have measured it on some class AB MMICS to quadrature match some PAs, but that was only for CW drive, and the phase would drift several degrees as the parts heated. The AM-PM are strongly tied to memory effects, and I suppose that's allot harder to measure and model.
Last Edit: 3 years 4 months ago by madengr.

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3 years 4 months ago #273 by Dave
Dave replied the topic: Phase distortion in PAs?
Thanks Mad.

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