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Design >> Mixed-Signal Design >> Distortion reduction by feedback
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Message started by ywguo on Oct 20^th, 2006, 1:59am

Title: Distortion reduction by feedback
Post by ywguo on Oct 20^th, 2006, 1:59am

Hi Guys,

If the second hamonic distortion is d2 for an open loop amplifier, what is it when the amplifier is put into a feedback loop? The open loop gain of the amplifier is A, the feedback factor is F.

Best regards,
Yawei

Title: Re: Distortion reduction by feedback
Post by vivkr on Oct 20^th, 2006, 5:22am

Hi Yawei,

It is not clear if the d2 in your expression refers to the distortion level or the
second-order coefficient in the input-output relation:

e.g. y(x) = a0 + a1. x + a2.x^2 + ...

Nonetheless, the important point is that you can improve the relation of the second harmonic to the
fundamental by a factor of (1 + AH)^2 when going from open-loop to closed-loop. Please see Razavi's book on
analog IC design (Chapter 13 on Nonlinearity and Mismatch).

Regards
Vivek

Title: Re: Distortion reduction by feedback
Post by ywguo on Oct 24^th, 2006, 9:29pm

Hi Vivek,

I want to know the relation of the second harmonic to the fundamental. It is clear in Razavi's book an analog IC design. Thanks

Yawei