guidance on the circuit analysis

Low Noise Single Supply Photodiode Amplifier

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? 

Thanks

  • Hey Walt

    Thank you for your reply, book and tutorials. currently I am doing a university project, we created  a sensor for sensing the sound wave, but current out signal from sensor is very sensitive to noise. I need to choose a Low noise amplifier.

    this circuit seems like a suitable opinions, I would like to modify this circuit by changing the amplifier of LTC6252 to a low noise amplifier, and then change the resistance value, capacitor value in order to get rid of the frequency below 20HZ and above 20KHZ, also with a high gain.

    and How can able to know its cut off frequency from the circuit? and even I use low noise amplifier, how can I maintain the external circuit noise? do you have any reference I  can read?

    Thanks so much for your help

    Muyuan wang

  • 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 choice. If you are going to be replacing the amplifier with a low noise op-amp from Analog Devices you should use ADIsimPE. Free down load available here:

    ADIsimPE powered by SIMetrix/SIMPLIS | Design Center | Analog Devices 

    You can use an ideal AC current source to inject a small signal current at the input and sweep the frequency to obtain the response of the overall circuit. The AC sweep can also do noise analysis. You can also run a transient analysis to measure things like step response or any other large signal tests.

    Doug

  • 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.

    Walt

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