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Design >> RF Design >> IP3 in mixers
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Message started by Superowl on Feb 25^th, 2005, 2:13am

Title: IP3 in mixers
Post by Superowl on Feb 25^th, 2005, 2:13am

I've been noticing that single-balanced MOS mixers have slightly better IP3 than double-balanced MOS mixers. Anyone have enlightenment as to why that's so?

Title: Re: IP3 in mixers
Post by vikas on May 10^th, 2005, 11:43am

As for as I know the IIP3 of the mixer or measure of linerity depends on the gate overdrive of the rf input. The higher the overdrive(Vgs-Vt) the better the IIP3 would be.

In single balanced case u might be using a transconductor as a V-I converter,wheras in double balanced case usualy a tail current source is also used for current matching purposes in left and right side branch. or to say to keep the IF amplitude constant. In that case the allowable overdrive of the RF input must have been reduced. And that could be reason for a lower IIP3. In my view if a tail current source is not used than one can expect the same IIP3 in both cases.

I am a self learner of RFIC design, so may be my analysis is fundamentally wrong. But i wish if somebody can correct me if I am wrong.

Thanks,
--Vikas

Title: Re: IP3 in mixers
Post by J on May 10^th, 2005, 12:17pm

are you assuming the RF goes into the transconductance stage and the LO goes into the switching stage? cuz that's what I was assuming.

Title: Re: IP3 in mixers
Post by vikas on May 10^th, 2005, 12:39pm

yes I am assuming that RF is fed in to V-I converter and LO to switching .

Title: Re: IP3 in mixers
Post by J on May 10^th, 2005, 3:29pm

The higher the overdrive(Vgs-Vt) the better the IIP3 would be .. can you refer to me a source that talks about this?

How would you determine the overdrive of current source, and why does a transistor have more overdrive than a current source?