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.
What noise bandwidth do you require?
How about a super-regenerative receiver with no input signal?
Look here:
Chuck
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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.
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).
-- John Devereux
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.
John
LM386?
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I have seen some designs using a CMOS invertor chain:
Wim
"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 battery. 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
Yeah, the RatShack amp uses a 386. That must have used a custom noisy version.
John
"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 f*ck up.
Should keep you quiet for a while.
...... Phil
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
Thanks for an actual data point, instead of an unsupported opinion.
Wow!
In this corner we have a nice black pot. What do I have for an opening bid?
-- Keith
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:
John
My opinion isn't unsupported. I have two of these boxes, and they both hiss.
John
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.
144 uV RMS is a pretty good amount of apparently-wideband noise, actually.
John
"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 f*ck up.
Should keep you quiet for a long while.
....... Phil
I work in picoseconds mostly, so time's up.
John
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