10 months ago
One real-world problem is, how do you make a wide-range bipolar reasonably-wideband accurate low-noise isolated resistor?
Some people do that with lots of resistors and relays, but electronic is more interesting.
Interestingly, Murata will make custom laser-trimmed metal film resistor arrays for pretty cheap. We're looking at using them in our next generation variable-gain amplifier box.
The working mechanism of the device is electrochemical insertion of the smallest ion, the proton, into an insulating oxide to modulate its electronic conductivity. At this stage, protonic resistor research reminds me of nascence OLED papers from 1990s. Sciencedaily's story source is an MIT press release:
It's time for me to return to my RPi2 BSD port of your OLED project. :) Danke,
Kilohertz, to simulate RTDs mostly. A user might scan/mux RTDs and might mux the excitation too, so we want sub-millisecond response but not RF.
Circuit puzzle: How do you make an electronic wide-range bipolar programmable resistor, say 0.1% accurate?
We just ordered some stock quad 100K thinfilm packs, about 30 cents each. You can make a mess of various values and dividers and opamp gains from one quad pack.
Probably a binary version of a resistor substitution box. Details obviously depend a lot on the voltage range required.
Yup. Our VGA gizmos use MDACs and switched resistors in various combinations, depending on the bandwidth required. The point of them is that the usual transconductance-based VCAs have really terrible noise performance for larger signals. (Barrie Gilbert patented an idea for using a whole lot of BJT pairs with their inputs wired in series to improve this, but you can't buy any like that now.)
Oh, another requirement is that resistance changes be monotonic and glitch-free. An RTD simulator souldn't spike to 300C when it's supposed to go from 25.2 to 25.3. Relay switched resistors have that problem.
fredag den 29. juli 2022 kl. 16.24.59 UTC+2 skrev email@example.com:
motorized potentiometer? :P
That's not so hard at kilohertz speeds--you can filter out the mux spikes.
with digital pots in audio it is called zipper noise, I believe some of them use the trick of only changing gain in zero crossings
For kilohertzy things you can use simulated inductors.
A resistor simulator that does RTDs can't do that. And can't, as far as I can figure, filter out relay transitions.
Not if it has to look like a resistor at all frequencies, right. But a kilohertzy device could look like a high-Z LC lowpass for nanosecond spikes. It would need a floating simulated inductor.
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