Roy ...

I've been playing around (ahem, excuse me, heuristically engineering) with
zener noise sources for a while using the same spectrum analyzer trick and
as yet I haven't been able to make the noise as "flat" across the passband
as I'd like. I've tried varying the bias, the voltage, and a few other
tricks, but as yet, no joy.

Can you shed some light on what you've found to make the noise power/voltage
fairly level across the band?

Jim




Some are very noisy. The noisiest I've seen have been ones in the 12 - 15
volt range when biased at considerably less than a mA. I've used one,
followed by a 50 ohm amplifier "pill" IC, as a broadband noise source to
see filter responses with a spectrum analyzer. The noise is easily visible
well up into the UHF region.

But all zeners generate some noise, so you have to use appropriate
filtering in sensitive applications. In my experience, though, band gap
references can be even noisier than a typical zener.

Roy Lewallen, W7EL