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Design >> Analog Design >> Charge injection in NMOS switch
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Message started by Nandish Mehta on Feb 28^th, 2011, 2:20am

Title: Charge injection in NMOS switch
Post by Nandish Mehta on Feb 28^th, 2011, 2:20am

Hi Friends,

As shown in the figure, the switches S1 & S2 are boot strapped. I have verified by simulations that across Vin from 0V to VDD, the VGS of S1 & S2 stays constant.

With VGS being constant, the charge injection on Cs is also finite and constant.

Now my question is, if I a constant charge is getting injected, how can I remove it?

Please suggest me some alternates

Title: Re: Charge injection in NMOS switch
Post by naderi on Mar 12^th, 2011, 7:33am

if the injected charge is constant, that introduces an offset to the integrator. There a few methods for offset cancellation at the input or output of the integrator. One could think of multi-phase operation, in which the offset is stored in one phase, and subtracted and canceled in another phase.
Fully differential integrator can also cancel out most of the injected charges as the charges are appearing at both inputs of the amplifier.

Ali

Title: Re: Charge injection in NMOS switch
Post by loose-electron on Mar 14^th, 2011, 2:01pm

Switched capacitor circuits have used charge injection cancellation techniques for many years.

Time to open a book or do some research, there's plenty of prior art out there on this topic.