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Design >> Mixed-Signal Design >> help about input filter of adc
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Message started by jeffyan on Feb 7^th, 2006, 3:33am

Title: help about input filter of adc
Post by jeffyan on Feb 7^th, 2006, 3:33am

hi all,

what is the best bandwidth of a filter needed at the input of an ad converter if one desires to convert
a signal at a specific speed and with a certain number of bits?

thanks in advance.
jeff.yan

Title: Re: help about input filter of adc
Post by venky on Feb 7^th, 2006, 7:46pm

There are several aspects which determine the choice of input filter for adc. It depends on whether you have SHA in the ADC or not, your bondwire inductance, whether you are driving it with a amp or through a transformer, how linear is the ON time of SHA switch, and of course on the sampling capacitor. I 'm also trying to design one such filter.
If you have SHA then the kick on the filter cap will be linear, otherwise the kick will be non-linear. The ON time of the sampling switch, (if it is a boosted switch) will also limit the linearity of the SHA's kick. If the series resistance that you put in the filter is very high then your transient settling might get affected. If the resistance is too small then circuit may start ringing because of bondwire inductance.