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  1. #1
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    transmission gate sizing

    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.

    •   Alt26th August 2009, 21:55

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    nsmission gate

    Quote Originally Posted by analog2003
    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.
    Quote Originally Posted by analog2003
    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.
    Quote Originally Posted by analog2003
    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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