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Design >> Mixed-Signal Design >> Optimal switch for Vdd/2 in a switched cap configuration
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Message started by eternity on Mar 30^th, 2015, 7:26am

Title: Optimal switch for Vdd/2 in a switched cap configuration
Post by eternity on Mar 30^th, 2015, 7:26am

Hi all,
Can anyone here suggest a reliable switch type (NMOS only, CMOS TG or a Bootstrapping switch) for switching a signal of magnitude Vdd/2. I tried with NMOS only and Bootstrapping configuration but ended up being imcompatible as I see a lot of tones in the output spectrum which degrades the dynamic specs of ADC significantly.

Thanks
Eternity

Title: Re: Optimal switch for Vdd/2 in a switched cap configuration
Post by carlgrace on Apr 2^nd, 2015, 10:11am

If you're seeing tones that means the resistance of the switch is changing as a function of the input. At VDD/2 I always use a CMOG TG. That way, when the PMOS starts crapping out the NMOS is driven hard and vice versa. CMOS TGs tend to be the most linear in my experience if you have a significant input swing.

Title: Re: Optimal switch for Vdd/2 in a switched cap configuration
Post by eternity on Apr 2^nd, 2015, 12:57pm

Thanks a lot
Indeed quite helpful