How to decide the value of sample capacitor

[Jenifer_gao]

Hi All:

If I design a sample and hold circuit for an A/D converter, for example, the A/D converter has 10 bit resolution. How can I choose the proper value for the sample capacitor.
Any suggestion will be appreciated. Thanks.

J

 

[mr_chip]

Its value is a trade-off between noise and speed performance. Since the thermal noise power is proportional to kT/C, larger cap will decrease the effect of thermal noise, but unfortunately it will increase the load of your op-amps or buffers..

 

[easytarget]

I would just try different values and make adjustments, based on the results. You don't have to design everything analytically. Also, if you're using a unity-gain sampler, increasing the sample capacitor affects the speed, but improves precision.

 

[chinito]

size of your sampling cap depends on what you're trying to do with switching cap. For example, if you're emulating an resistor then Req = 1/(C*Fs). If you're implementing an inverting integrator, gain dictates the sampling cap (Ki = -(C1/C2)*Fs and so on.

 

[vistapoint]

So can anybody give an example, 1pF or 100fF?