I am trying to understand the circuit shown above, with one JFET transistor at left side acting a current buffer and right hand side with a op amp.
this is a low noise transimpedance circuit, which I think I can use or modified this circuit and used in my design, sensitive to noise and a current signal needed to be amplified to voltage signal in the end.
the problem is that I am not quit sure how to analyse the circuit, should I use small-signal analysis? Do I need to derive the transfer function?
why the Bandwidth is 2MHZ and where is the cut off frequency? and is the system stable or not?
Can someone give me a clue or answer, please?
Due to an operator error (mine) my original reply was accidentally deleted. I will try and reconstruct it:
The circuit came from a respected manufacturer's archive of application notes, and the pulse response shows no ringing--therefore it looks stable. The bandwidth is determined by R1 and the parasitic 0.08pF capacitance. 1/2piRC ~ 2MHz. However, depending on a 0.08pF parasitic capacitor could be problematic.
There are many tradeoffs in designing a low noise, high gain, high bandwidth photodiode preamp, and you might want to check out some of our literature on the subject:
Sensor Signal Conditioning, Chapter 7
MT-035, MT-050, MT-059
We also have several photodiode amplifier reference designs complete with documentation that are available for a nominal cost:
CN0272, CN0312, CN0363
And also a design tool specifically for photodiode preamps: Photodiode Wizard
Let us know if you have any further questions.