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Reference Voltage Schematic

Helmut is not wrong; we're all saying the same thing. U(out) = Vbe(Q2) - Vbe(Q1). Helmut was just kind enough to elaborate on the temperature stability and such.

Measured, with real transistors.

Uo is already pretty "good," in the sense that the temperature coefficients cancel pretty well, but the voltage itself is small and strongly dependant on Vbe matching between the transistors. That makes Uo essentially unpredictable.

To square up a TTL waveform to precision levels, it looks to me.

Cheers, James

Reply to
James Arthur
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Hi James,

just I don't see the sense herein.

Marte

Reply to
Marte Schwarz

'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

Reply to
James Arthur

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

Reply to
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

Reply to
James Arthur

BTW, how does one measure noise of references?

Reply to
Robert Baer

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

Reply to
James Arthur

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