Low volt noise gen

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).

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

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.

1. Phase noise of a CMOS invertor chain

Wim

"Spehro Pefhany"

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"

- learn to shut the f*ck up.

Should keep you quiet for a while.

...... Phil

Take your own advice, Phillis.

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?

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.

John

"John Larkin" John Popelish

Or any sane thought.

- 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