A capacitor won't filter much when you drive it from a near-zero impedance and micropower voltage references are generally quite noisy, so it's probably better to put an RC noise filter in between the reference and the op-amp - but then again, Jan didn't specify noise requirements.
If noise and inductance don't matter you could use a TS4061 or similar shunt regulator IC.
If noise and inductance don't matter you could use a TS4061 or similar shunt regulator IC.
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Stop beating around the bush, bite the bullet and use a 1.2V one: it will have an inexistent dynamic resistance, zero tempco, and it's only a single partIn fact it starts to look like those ic shunt regulators ...
Same as above, just adjustableBrain fart: how about a 3-terminal voltage regulator that could sink current?
OK OK< stop twisting my arm ;-)
Recap: my query originated from trying to use a 2-diode drop 'thingy' as cathode resistor in a small signal tube circuit (no I won't show the circuit).
Then I looked at the diode-drop variation with current, and I thought: which type of diode would have the lowest voltage drop variation, ie. the steepest V/I slope, hence the 'physics' question.
And look where we ended up! But, as often here, I learned several things on the way, for which I thank all of you.
PS Yes there are 1.2V shunt references, but they have noise and cost upward from $6. I do have a Dutch reputation of frugality to uphold.
Jan
Recap: my query originated from trying to use a 2-diode drop 'thingy' as cathode resistor in a small signal tube circuit (no I won't show the circuit).
Then I looked at the diode-drop variation with current, and I thought: which type of diode would have the lowest voltage drop variation, ie. the steepest V/I slope, hence the 'physics' question.
And look where we ended up! But, as often here, I learned several things on the way, for which I thank all of you.
PS Yes there are 1.2V shunt references, but they have noise and cost upward from $6. I do have a Dutch reputation of frugality to uphold.
Jan
... Yes there are 1.2V shunt references, but they have noise and cost upward from $6. I do have a Dutch reputation of frugality to uphold.
- AZ432BZTR-E1
- 1.25V
- ±1%
- 0.15 ohms dynamic impedance (guaranteed MAX spec)
- 20ppm/°C Typical
- $0.293 (qty=10)
Sales page at digikey
Only 625 of them on the shelf. Buy 25 pieces right now.
My educated guess would be around 70 nV/sqrt(Hz), assuming that it uses a simple bandgap with 8:1 transistor and 1:1 current scaling (which is suboptimal, but only slightly) and that most of the minimum cathode current for regulation flows through the bandgap reference. But that's only a guess.
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