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apd frequency response

Discussion in 'Electronic Design' started by [email protected], Aug 22, 2007.

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  1. Guest

    I got a task from my professor to explore pulse response of APD.
    The APD is Hammamatsu APD module C5331 and it has bandpass frequency
    (4 kHz~ 100 MHz)
    To find the response of the detector to given pulse
    signal(square ) ,I think that I need to know
    exact frequency response formula of the APD module.

    I don't know the origin of bandpass response exactly.
    Is it from some internal filter circuitry?
    Or..does it have another origin?

    If it's from bandpass filter inside the module, it will be possible
    apply the formulas from electronics .
  2. Usually the roll off at higher frequencies is
    due to the diode capacitance which is proportional
    to the area of the diode. Therefore the faster
    diodes have less area.

  3. Guest

  4. The frequency response of the APD module is determined by the capacitance of
    the APD itself and the gain/phase response of the transimpedance amplifier
    cascade connected to the APD. Generally, the overall response is a lowpass
    function of the 2nd order.

    Vladimir Vassilevsky
    DSP and Mixed Signal Consultant
  5. John Larkin

    John Larkin Guest

    As mentioned, it's a combination of the diode capacitance and
    amplifier response, if any.

    Either get Hammamatsu to supply the data, or measure it
    experimentally. A cheap laser diode, like a Lasermate VCSEL, driven by
    a good pulse generator, can generate a pretty clean light step or
    impulse with 100 ps risetime. A sub-ns impulse would be ideal for
    characterizing your gadget.

  6. LVMarc

    LVMarc Guest

    Professors are funny that way :0)

    first cut analysis is as follows:

    treat the system as a first order low pas filter with a 100 MC upper

    Then the response to a step is the derivative of impulse response of the
    filter function, itself.

    therefore the out put to a step will be a rise time limited signal ,,
    the rise time will be about 3.42 nS in this case. you will have to
    derive this or produce the bw and rise time relation ship.

    the low frequency of 4 KC means that if you have a single step from "no
    light" to "light" then you get this 3.42 nS rise tie limited signal..
    the 4 kc low frequency mans, the system is "AC coupled" and the step
    output will begin to droop relitve to the 4.2 mS time frame. normally
    for the interesting light signals are pulsed signal 10 - 500 nS wide so
    the droop you get with a 4 KC low frequency cut -in is minimal.

    Best regards and happy designing


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