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transmission gate sizing

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analog2003

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Hi,

I am unable to decide how to size a transmission gate. I sized them in the ratio of their unCox. The delay is not a huge concern, because the sampling capacitance is very small. Is that it, or some other factor like channel charge injection has to be considered?

Thanks for your help.
 

erikl

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nsmission gate

analog2003 said:
I am unable to decide how to size a transmission gate. I sized them in the ratio of their unCox.
In most cases, equal w/l ratios for both p- and nfets are used. But sizing according to their µCox-ratio is also fine, I think.
analog2003 said:
The delay is not a huge concern, because the sampling capacitance is very small.
Make the w/l as small as possible, just big enough for your max. delay requirement. If 2 or more transmission gates have to match, consider the necessary w*l product for your matching requirement.
analog2003 said:
Is that it, or some other factor like channel charge injection has to be considered?
Channel charge injection very often is a problem. Consider at least the simplest compensation method with (1/2)*(w/l) anti-phase-switched drain-to-source-shorted compensation fets.
 
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