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[SOLVED] suitable substitute for ADC inputs to use as load in simulation tool

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d123

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Hi,

What's a suitable approximate substitute of a dual slope ADCs inputs? It is to use as a relatively realistic load for an OA voltage follower. Datasheets and app notes say next to nothing helpful.

From scant info I did find, and common sense reasoning, most obvious is any OA with (suitable bandwidth and) similar input impedance to 1000M and 86dB CMRR at +-1V in.

For what reasons might these two manufacturers' datasheets and assorted app notes, and other manufacturer's datasheets, for this specific part not say what input capacitance is and explicitly state what input impedance actually is? They seem like important parameters to include, to me.

If it helps:

ADC equivalent input for sim model.jpg
 

I found the attached document in another folder about ADCs whilst looking for a schematic that was two (in parallel) series resistors with caps to ground and a common cap linking in+ to in-, which I haven't located yet. That might help. It's actually far more complicated than at first thought as the switches, or at least adding a series switch, affect 'reasonable representation' a lot if excluded and only OA and filters used and use static mOhm resistor as Zin, not useful as is not an impedance, though.



Useful SC ADC single input equivalent.JPG
 

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  • Useful Things to Know about High-Speed AD Converters slyp171.pdf
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