Voltage peak detetctor

[kirkr]

I have designed a opamp based voltage peak detector. As shown in the diagram below. however the output voltage only follows the input I thought i had the cap sized right to hold the value longer. The input wave is only about 1ns or smaller pulse is the goal.

 

[keith1200rs]

Test it with a slow waveform first.

Is that a PMOS or NMOS? I would expect NMOS as common drain.

Keith

 

[kirkr]

That is a pmos. I will try with a slow wave first. thanks

 

[keith1200rs]

It should be an NMOS source follower, I would have thought. As a PMOS you have introduced and inversion and so have positive feedback.

Keith