Input capacitance (AD8601)

Sebastien69 on Oct 15, 2019

hello,

i would like to know the input capacitance value (common) of the AD8601 amplifier.

If not known, do you have a method to estimate/measure it ?

I would like to put a follower in parallel of a capacitor to measure its voltage charge. But input capacitance of amplifier is measure as a parasitic parameter.

if you have any idea...

thank you

Sebastien

0 ADIApproved

on Oct 16, 2019 12:55 AM
Hi Sebastien,

I have attached a slide on how to measure common-mode capacitance.

There is another way on how to measure it, which is described in this article by Glen Brisebois https://www.analog.com/en/technical-articles/signal-conditioning-for-high-impedance-sensors.html

Opamp_Ccm_measurement.pptx

You might also want to check this article https://www.analog.com/en/analog-dialogue/articles/direct-method-of-measuring-op-amp-input-differential-capacitance.html

Regards,

Arthur
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0 dhaas on Feb 4, 2022 1:07 PM

Hello Sebastien,

Common mode:

I performed a rough measurement and got ~ 7pf . @ -3db (117.3kHz)

My pcb for the test circuit had a parasitic capacitance of 2.78pf and my probe has 3.9pf of capacitance. I subtracted these from the results of my measurement.

measurements were done with a single 5v supply.

hope this helps,

Dan
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