Hi all, I picked Mark Johnson's "Photodetection and Measurement" book off my shelf. Reading in chapter 4 he talks about PD-TIA designs that use optical feedback rather than a resistor. Book is here,
If you 'look inside' and search for Figure 4.1 you can find it. But it's simple. Voltage from TIA runs an LED (with resistor) and light falls on a second PD that cancels current from PD one is using as a detector. (Do you need me to draw a picture?)
Voltage -> current, an optical resistor. He gives a few references (all behind pay walls.)
Anyway it seems like a fun idea. (With it I could eliminate my switch capacitance from the TIA feedback, at the cost of more shot noise. And some DC offset on the output.) It would need a good LED whose light output vs current was linear. Or some good fast opto-isolater that uses an LED and PD.
I don't know of any.. (Isolators or linear LED's) I think James A, mentioned a more linear LED a few months ago?
Thoughts? George H.