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Design >> Mixed-Signal Design >> reference buffer for SAR A/D ?
https://designers-guide.org/forum/YaBB.pl?num=1335815704

Message started by Ajay on Apr 30^th, 2012, 12:55pm

Title: reference buffer for SAR A/D ?
Post by Ajay on Apr 30^th, 2012, 12:55pm

I have a SAR A/D converter and I need to make a reference buffer for it. The buffer has a big capacitor of a few micro-Farad connected to it. This acts a voltage source for the capacitive DAC array. What type of an op-amp architecture do I use for the buffer ? A 2 stage miller compensated opamp may not be suitable since the compensation cap. will be in pico-farad only. Any ideas / suggestions will be appreciated. Thanks.

Title: Re: reference buffer for SAR A/D ?
Post by carlgrace on May 11^th, 2012, 1:25pm

Single-stage op amps get more stable as you increase the load capacitor. Since you have such a large cap, maybe you should look into a single-stage op amp buffer.

Title: Re: reference buffer for SAR A/D ?
Post by pixel on May 18^th, 2012, 3:00am

In this case type of the output stage and buffer speed are specially important.
What is the resolution clock frequency and total DAC capacitance of your ADC?

Title: Re: reference buffer for SAR A/D ?
Post by loose-electron on May 24^th, 2012, 1:30pm

you are driving a capacitive load.

OTA with a push pull output.