Question about sample and hold circuit.

[EDA_hg81]

Should the turn on time of MOSFET be longer than 5RC?

Then cap can get the stable input voltage and hold this voltage till MOSFET turn on again?

Which wideband FET can be used as the Buffer next to sample and hold cpa?

Thanks.

 

[kspalla]

Should the turn on time of MOSFET be longer than 5RC?

Theoretically "yes"
This comes with the specification of max frequency signal that you need to sample and hold.
Obviously you have control on selection of RC values to achieve it.

Then cap can get the stable input voltage and hold this voltage till MOSFET turn on again?

yes

Which wideband FET can be used as the Buffer next to sample and hold cpa?

FET should be ultra fast switch.