I need to amp up an rgb photodiode (3 diodes for each channel), however the diodes are connected with common cathode. All the amp circuits that I have looked at connect cathode as a unique channel. Therefore I can’t extract each channel.

Can I please have some suggestion?

Vf = 0.5-1.3V
Vr = 10V

 

My suggestion is: tell us what "amp up" means. Or what you want to do.