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  1. #1
    Newbie level 4
    Points: 857, Level: 6

    Join Date
    Oct 2012
    0 / 0

    Photodiodes and Transimpedance amps

    Hi All,

    I have been set a task by my mentor which is the following:

    Consider a transimpedance amplifier (https://en.wikipedia.org/wiki/Transimpedance_amplifier).

    This should be a real (non-ideal) operational amplifier, such as the OPA627: (http://www.ti.com/lit/ds/symlink/opa627.pdf).

    Contrast the design challenges of designing this circuit to amplify the signals from a silicon photodiode S1133-01


    compared to a P10090-01 InAs photodiode


    You should consider at the equivalent circuit of a photodiode attached to the non-ideal amplifier and consider amplifier performance in relation to the shunt resistance of each photodiode in the two cases. Is anything else important?

    So far I have

    So far I have determined the following problems identified:

    Feedback factor / capacitance of opamp input and sensor putting stain on opamp to compensate
    High required GBP required due to preference for high gain / large value of Rf. This limits sensitivity
    Johnson noise (ij) from low shunt resistance for the InAs which changes with temperature
    Dark noise current from visible light on InAS?
    Shunt resistance drastically changes with temperature for both sensors but worse with the S1133-01

    Mainly from
    Page 11-16, page 22-23

    If anyone can help further I'd really appreciate it!

    •   Alt3rd January 2017, 02:49



  2. #2
    Advanced Member level 2
    Points: 5,019, Level: 16

    Join Date
    Sep 2004
    79 / 79

    Re: Photodiodes and Transimpedance amps

    Hi mat09,
    it is important to note that Si photodiode is used in photocondutive and InAs in photovoltaic mode.

    Photoconductive mode:
    Si diode is negatively biased (therefore large shunt resistance) and in first approximation is capacitance Cd.
    Because of speed, stability and noise performance this capacitance should be kept small as possible.
    This is the reason that inverse voltage sholud be large as possible (diode C-V characteristics).
    In oreder to optimize TIA noise GBW of th amplifier should not be too large.
    At the other side if it is too small circuit would be unstable.
    Cf can be used for stabilization but it has also direct influence on speed BW~1/(2piRtiaCf)

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