Peak Detector Not working

[omar_Bakheet]

I designed this folded cascode to give me a gain of 63 dB and a GBW of 200MHz , I am using this to make the following peak detector

The Vpeak signal doesnt seem to be following the input signal ( frequency 20MHz)

 

[Easy peasy]

how are you re-setting or pulling down the capacitor ?

at the moment it can only go up in volts

 

[omar_Bakheet]

how are you re-setting or pulling down the capacitor ?

at the moment it can only go up in volts

On cadence, it seems to be discharging but am not sure where, I tried connecting a large resistance in parallel and placing a small bleed current source and the issue remains

 

[KlausST]

Hi,

What - in values - is the exact issue?

You need a scope to verify it. And for sure you might see a higher value because of noise and hum .. but you might see lower value because of too weak charging current or too high capacitive coupling from gate.

You need to go into details if you want good answers.

Klaus

 

[dick_freebird]

Failure-to-follow might be from an overloaded output
or bad bias rails or a bad input common mode position
or....

Debug time, not rando wild guess time.