avalanche diode noise circuit

Discussion in 'The Projects Forum' started by cbecket13, Nov 15, 2014.

  1. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    I built this project with a few minor mods;

    http://www.edn.com/design/analog/4420926/White-noise-source-flat-from-1Hz-to-100kHz

    It generates fairly good noise which is closer to "blue" noise up to 11025 hz.

    But I read that by reducing the reverse bias current near the breakdown "knee", instability and extreme sensitivity can be induced in the output signal. That is, perhaps strangely, exactly the effect I want.

    So the question is: how do I modify the circuit to put it in this unstable mode?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,651
    632
    [​IMG]

    Above is the noise I measured in microvolts RMS while varying the bias current current (X axis; actually voltage from an adjustable power supply into a 25.5k resistor connected to the Zener's cathode.) through an 1N4735A. The slope of noise as a function of current, gives the highest sensitivity to current a little past the knee.

    If you want the amplitude of the noise to be unstable you use a current source that varies with temperature, time, or some other factor and adjust the bias current on the slope between the knee and the first peak.
     
  3. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Thanks. What did you do the analysis with?
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    The noise was measured at the output of U2A in the circuit below while the 10k pot was used to vary the voltage on the cathode of the TL431. The voltage drop across the 1N4735 was calculated as the difference between the cathode voltages for the TL431 and the 1N4735, which was measured with a digital voltmeter.

    The noise output was measured using a true RMS meter basted on the Analog Devices AD737 RMS to DC converter connected to a digital voltmeter.

    [​IMG]
     
  5. cbecket13

    Thread Starter Member

    Nov 15, 2014
    106
    3
    Interesting. Seems like a lot of trouble too go to for my little problem. Thanks. I'll post my little test circuit when I get to work. I think I've found the "sweet spot" on a reverse-biased transistor. The resulting response was interesting.
     
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