How to design good input buffer?

[ccw27]

What circuit topology is usually used to design good input buffer for driving 1)capacitance 2) passive S/H? Source follower or Unity-gain diff-amp? And how to size the transistors so a low output distortion is obtained.

Thanks

 

[huanchou]

The circuit structure is by your application. For the sizing issue I suggest you can try to run the divice current vs. device length curve and differentiate it, then you can get the ideal device length.

 

[ccw27]

I am using shunt negative feedack buffer to drive a CMOS switch with 0.8 pF capacitance at the output. I am only getting a distortion of less than 25 dB. How can I decrease the output distortion further?

Thanks