Electronic – Reduce Input Capacitance Transimpedance


I'm designing a readout circuit for a photodiode consisting of a transimpedance amplifier. I've noticed that the photodiode has a relatively large capacitance (320 pF). Are there any tricks/adjustments I would need to compensate for this capacitance (in terms of speed and noise)?

Best Answer

Yes, there are many things beyond the textbook transimpedance amplifier configuration.

For example, you can use a cascoded transimpedance amplifier and bootstrap it to reduce the effect of the PD capacitance. Dr. Phil Hobbs is an expert in this subject, and I would recommend his book on Electro-optical Systems. Here's an article on the subject that is freely downloadable, and below is a schematic for such a PD front end. The BFG25 acts as part of the cascode, and the MPSA18 provides the bootstrapping.

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This is by no means the final word on PD front ends, but the major ideas are present. When the FB resistor has to be very high value (G ohms), another set of tricks comes into play.