[Laser] DC couple the K3PGP amp?

[J. Forster]

F1AVYopto at aol.com wrote:

[snip] It  is not the inter stages capacitors effect but the RC time constant
effect

>  from the internal photodiode capacitance and its internal resistor
> associated  with the FET impedance.
> If  we calculate the Fc = 1/2 pi RC even with very fast PIN photodiodes, the
> -3  dB cut off frequency is always lower than 100 Hz. [snip]

If you want frequency response from a photo diode, back bias it to widen the Space
Charge Layer and run it into an opamp input (a virtual ground)  with a FB resistor.
It works well to > 1 MHz.

-John