Reference Voltage Schematic

Hi James,

just I don't see the sense herein.

Marte

'Scope calibrator? Or, useful in a charge-packet type analog circuits, like a frequency-to-voltage converter, or certain charge- balancing analog-to-digital converters.

These days, though, I'd just use a CMOS gate to do this.

James

Make sure the LED is not subjected to varying light levels.

Back when you could still get low voltage true Zener diodes, I did a reference using a ring-of-2 arrangement with a couple of 2.2V diodes and discrete PNP/NPN transistors. It was pretty reasonable stability for a discrete design, and much lower noise than available from a bandgap or avalanche mode diode.

Regards Ian

Yes, quite important--I should've mentioned it.

The ol' "I'll stabilize your current if you stabilize mine?" (aka "pushmepullyou") Nice.

Cheers, James

BTW, how does one measure noise of references?

I've not done it, but not much different than for op amps, AIUI. Amplify with a low-noise amplifier, then examine with a spectrum analyzer.

I've got an old article where Walt Jung measures his ultra-clean reference's noise using an AD797 in a x100 non-inverting a.c. amplifier, then a.c. couples the output into a noise analyzer.

Best, James Arthur