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Low volt noise gen

Discussion in 'Electronic Design' started by Larry Redmore, May 9, 2007.

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  1. I am looking for a circuit that will generate random noise and run on
    a supply as low as 4 volts. Typically, this cannot be done with diode
    or transistor junction noise. The minimum potential seems to be around
    9V. To overcome this, simulated noise is sometimes generated with
    digital IC's, but this is not truly random.

    Does anyone know of a circuit that will generate genuine random noise
    and operate down to 4 volts, without specialized components?

    Larry R.
  2. Andrew Holme

    Andrew Holme Guest

    What noise bandwidth do you require?

    How about a super-regenerative receiver with no input signal?
  3. Chuck

    Chuck Guest

    Look here:
    Junction Noise Measurements I

  4. rebel

    rebel Guest

    Why not use a switchmode step-up and generate the higher voltage from your "down
    to 4 volts" source? Of course, you'll have to filter the output carefully to
    avoid a noise contibution.
  5. Depending on your definition of "truly random", you could use a
    cascade of ac-coupled opamp stages to amplify the noise from a high
    value resistor (e.g. 10M).
  6. John Larkin

    John Larkin Guest

    And there are some truly terrible opamps around, with noise density
    scores of times higher than a resistor.

    What's that National dip8 audio power amp, the one in the Radio Shack
    amp/speaker boxes? That hisses like gangbusters.

  7. LM386?

    Best regards,
    Spehro Pefhany
  8. Wim Ton

    Wim Ton Guest

    I have seen some designs using a CMOS invertor chain:

    1. A chain with a variable length. The length is controlled by some LFSR
    outputs and the read strobe
    The input of the LFSR is the output of the invertor chain, latched by a
    crystal clock.
    The random is an output of the LFSR.

    2. Phase noise of a CMOS invertor chain

  9. Phil Allison

    Phil Allison Guest

    "Spehro Pefhany"

    ** No way - the LM386 is very quiet.

    From myself on SED Jan 22 this year:

    " Natsemi do not supply a noise spec for their LM386 audio amp.

    I used the most basic circuit with a gain of * 26 dB * and fitted a 47uF
    bypass cap on pin7.

    Input pins 2 & 3 were grounded to pin 4, DC supply came from a 9 volt radio
    The output signal on pin 5 was fed first to a 60dB gain mic pre-amp and then
    a 22Hz to 20 kHz audio band filter with 12 dB/ oct roll-off slopes.

    The noise signal was observed on a scope and found to be hum free, then
    measured with a True RMS voltmeter with over 100kHz bandwidth. The reading
    was 144mV rms.

    So, the LM386's output noise level was 144 uV rms.

    Relative to a 3 volt rms output level, the s/n ratio is around 87 dB.

    Fine for the intended applications. "

    ........ Phil
  10. John Larkin

    John Larkin Guest

    Yeah, the RatShack amp uses a 386. That must have used a custom noisy

  11. Phil Allison

    Phil Allison Guest

    "John Larkin"
    "Phil Allison"

    ** Explanation snipped out of sight by Mr Ego Larkin ....

    ** When you have nothing sane to say John

    - learn to shut the **** up.

    Should keep you quiet for a while.

    ....... Phil

  12. Take your own advice, Phillis.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  13. Thanks for an actual data point,
    instead of an unsupported opinion.
  14. krw

    krw Guest


    In this corner we have a nice black pot. What do I have for an
    opening bid?
  15. John Larkin

    John Larkin Guest

    I have no object in life other than to amuse myself. So go fill out
    some complaint forms or something.

    Here, this should get you started:

  16. John Larkin

    John Larkin Guest

    My opinion isn't unsupported. I have two of these boxes, and they both

  17. Is the hiss originating from the LM386 chips or from some
    other component? Phil's data shows the result of a test of
    the LM386 generated noise.
  18. John Larkin

    John Larkin Guest

    144 uV RMS is a pretty good amount of apparently-wideband noise,

  19. Phil Allison

    Phil Allison Guest

    "John Larkin"
    John Popelish

    ** It's totally unsupported by objective data.

    Or any sane thought.

    ** When you have nothing sane to say John

    - learn to shut the **** up.

    Should keep you quiet for a long while.

    ........ Phil
  20. John Larkin

    John Larkin Guest

    I work in picoseconds mostly, so time's up.

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