Bandwidth of a Transimpedance Amplifier

Hi Hari,

add the equivalent circuit model of photodiode with detector capacitance and parallel resistance and add the obligatory phase lead capacitance in parallel to Rf and you will see the answer. One more tip: Consider the noise gain of this circuit

Kai

As Kai said Hari, you need to complete the design with a source C and feedback Cf. In general, you end up with a 2nd order transfer function modeling the op amp as a single dominant pole - this is a good simplification for most designs as the feedback noise gain cross the Aol curve well before any higher frequency Aol poles. The simplest design point is to set the feedback Pole location at 0.707 * the geometric mean of the zero caused by the source C and Rf and the Gainbandwidth product. If you do that, you get a closed loop Butterworth response with a F-3dB at that geometric mean frequency. More generally, you get a 2nd order response which could be peaking. Here is a complete treatment with some good simplifications, 

1882.Transimpedance design flow using high speed op amps.pptx

Hi Michael and Kay,

Thank you for your time.

If my photodiode is ideal then can I divide GBWP by Rf.

Regards

HARI

Hi Hari,

you might want to read this:

https://en.wikipedia.org/wiki/Transimpedance_amplifier

Kai