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shot noise source

Discussion in 'Electronic Design' started by [email protected], Sep 19, 2005.

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  1. Guest

    (I posted this two hours ago without a result, so please don't be
    offendet if you see two messages)

    Hello,

    I need to build a white noise source from 1 Hz to 10 kHz (the more the
    better)
    and came across a photodiode shot noise source which seems fine because
    it can
    be calculated and I don't have the facilities to calibrate a zener
    noise source.

    Message from Phil Hobbs
    http://groups.google.com/group/sci....=

    Now I need a concrete design idea:


    a) use an inverting amplifier with a big feedback resistor (1 G)
    Illuminate the diode for 1 nA Photocurrent.
    This gives me 1.8e-14 A/sqrt(Hz) current noise,
    with 10 KHz bandwidth 1.8 mV after the amplifier.
    LF411 has around 10 fA/sqrt(Hz) noise, this is not negligible with
    respect to the shot noise.
    In addition, johnson noise from the feedback resistor is to large,
    since
    the voltage is below 50 mV (2kT/e)

    b) use 1 mA photocurrent and see how to get rid of the DC before
    amplification.
    Use the active load circuit from Zetex application note AN3, figure 6.



    ------|------- +Vee
    |1k5 |
    ..-. |33n
    | | ---
    | | --- ___
    '-' | ||___||
    | | | |
    | | 330k | |
    |---|-|___|--------------|-\ | ||
    /| | | >------||-
    | | GND-|+/ ||
    |-------------- |/| out
    -
    ^
    |photodiode
    |
    |
    ------------ -Vcc
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


    Probably I would use a current source to sink the current from the
    photodiode
    and use negative feedback from the output of the OPA to the light
    source to have
    a better response at low frequencies

    Do you have any comments?

    Many thanks for your feedback


    Daniel
     
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