OPA859-Q1: What are "Common-mode input capacitance" and "Differential input capacitance"?

Yoshiki Ochi

Part Number: OPA859-Q1
Other Parts Discussed in Thread: THS3062

Hi team,

What are "Common-mode input capacitance" and "Differential input capacitance"?
Do you have equivalent circuit model for explaining them?

Transimpedance amplifier looks low input capacitance value, is it correct?

Regards,
Ochi

over 3 years ago

+1 kai klaas69 over 3 years ago

Guru 140200 points

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/input-capacitance-common-mode-differential-huh

Kai

0 Sam Burnett over 3 years ago in reply to kai klaas69

TI__Expert 3620 points

Thank you Kai, posting the snapshot for convenience:

Best,
Sam

0 Michael Steffes over 3 years ago in reply to Sam Burnett

Guru 48395 points

And, since this comes up so often, here is an extraction article and why. Essentially, if we take the TINA models as perhaps off some of the time (e.g. THS3062 discussion) this talks about testing and fixing those externally.

https://www.planetanalog.com/input-impedance-extraction-and-application-for-high-speed-amplifiers-insight-9/#

For a transimpedance design, with the V+ node at ground, you add the Cdiff and one Ccm on the inverting node to the source C for design purposes.

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OPA859-Q1: What are "Common-mode input capacitance" and "Differential input capacitance"?