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?
To test out your circuit I would recommend you use circuit simulation software like some version of SPICE. If you are looking at the circuit you show which uses an LTC amplifier, LTSpice would be the best…
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.