small input capacitance in ADC

[Osawa_Odessa]

Hello,
I have read that in ADC it is desired to have a small input capacitance. Could anyone explain to me the reason?

 

[GUMY]

To filter the noise and to minimize voltage drop caused by sample cycle of ADC, thus minizing ADC error.

 

[crutschow]

The input capacitance acts as a load to high frequency input signals so, if you are trying to convert a high frequency input, you want minimum input capacitance to minimize the requirements on the source that provides the signal to the ADC input.

It has nothing to do with filtering noise.

 

[GUMY]

I was talking about DC and LF signals and You are talking about HF signals.

 

[D.A.(Tony)Stewart]

It is best to use small plastic cap vs ceramic for various reasons. Ceramic is a poor choice for sample and holds with memory issues creating noise.

 

[crutschow]

I was talking about DC and LF signals and You are talking about HF signals.

I think the problem is semantics. I took the OP's statement literally and though he was referring to the intrinsic input capacitance, but you inferred that he is talking about adding a small input capacitor. You probably are right. :-?

English is a tricky language. :wink: