I'd like to create a random number generator based on thermal noise from a resistor, using an opamp to amplify the noise and an inverter to convert the resulting spikes into a digital signal.
Here's my current design:
When I remove R5 and feed Multisim's thermal noise source (set to 10M ohm / 27C / 1MHz bandwidth) I get perfect results. The output of U2 is noisy, the input of U1A ranges from roughly +12V to -12V, and the output of U1A gives me a random-ish digital output. I plan to feed this to a PIC and do bias correction on there.
The problem is that Multisim's resistors are ideal, or at least ideal enough to not produce any noise. As such, I can't test this. Will it work as I expect, or am I missing something?
I've split the opamp into three stages and introduced a second 10M resistor to make the input midscale. I now get a much higher bandwidth output and my gain is about 10,000.
Ok, I think we're getting there. Some resistor values have been tweaked, and a midpoint has been added.