1
\$\begingroup\$

I've been experimenting with three-valued logic (yeah, I know) and have had quite a bit of success by using voltage comparators to implement the combinatorial logic. All 27 1-input gates and many useful 2-input gates are functioning as expected. The progress is documented at https://hackaday.io/project/6284-tern-physical-implementations-of-ternary-logic

The problem comes about when I start getting into sequential logic. Specificly, SR latches, D Flip Flops, etc. Just elementary memory elements. Not only do the circuits become quite complex but they also exhibit behavior I just don't anticipate. I'm not knowlegable enought in analog design to debug them and I don't even own a scope so I'm nearly blind as well. However, I do know that this is a solved problem because Flash chips use anywhere from 2 to 8 (maybe even higher) voltage levels. Because this stuff already exists in the realm of integrated circuits I'm not going to be picky about staying strictly away from binary-digital solutions for storage.

What I'm looking for is a relatively simple solution that will fit within these parameters: 1) will accept an input voltage between -5V and 5V 2) will store that voltage until directed otherwise (volatile is okay) 3) will output that voltage while it is stored 4) is available in a dip package

My best case scenario (even though it doesn't exist) is a family of dip IC's that are analog equivalents to 8 bit latches, shift registers, etc. My worst case scenario is throwing an arduino into the mix to read analog voltages and PWM them out.

I'm looking for a solution that falls inbtween the two. Is there a family of multi-input sample and hold chips that will keep a charge for a reasonable amount of time (at least several minutes). Or maybe an ADC with PWM output that can hold a level until directed and can accept -5 volts. Any other ideas? Thanks much for your help!

\$\endgroup\$
2
\$\begingroup\$

What I'm looking for is a relatively simple solution that will fit within these parameters: 1) will accept an input voltage between -5V and 5V 2) will store that voltage until directed otherwise (volatile is okay) 3) will output that voltage while it is stored 4) is available in a dip package.

Looks like a sample and hold IC is what you're looking for. The LF398 fits your requirements. There are lots of other chips that do the same basic function with different trade-offs. I've seen sample and hold IC's with multiple channels as well.

Note that analog sample and hold circuits are never ideal. You will see the output voltage drift over time. You can minimize this effect by doing good pcb layout and picking high quality components, but the effect will always be there.

\$\endgroup\$
  • \$\begingroup\$ wow, 5mV/Sec droop. The reason I didn't already go with a sample and hold is because I kept seeing droop rates of .1V/Sec and so forth. \$\endgroup\$ – Rory O'Hare Dec 22 '15 at 4:08
  • 1
    \$\begingroup\$ You want a really good low leakage capacitor for this (polypropylene or polystyrene), and you'll better put the circuit on a pcb, not on a solder-less breadboard. Cleaning off all flux from soldering is very important as well. \$\endgroup\$ – Nils Pipenbrinck Dec 22 '15 at 4:16
  • 1
    \$\begingroup\$ Hm. Makes me wonder if it's possible to adjust these by adding some sort of two-level hysteresis or to make the voltage "snap" to either VCC, 0, or VEE. Basically as it stands, it will leak down to 0, so a 0 will hold indefinitely. Just needs something non-linear that will add positive feedback if it's high enough.. Hmm! \$\endgroup\$ – pipe Dec 22 '15 at 4:16
  • \$\begingroup\$ I'm looking at the SMP04 from Analog devices now. Looks like it has similar characteristics to the LF398 but in a quad package. \$\endgroup\$ – Rory O'Hare Dec 22 '15 at 4:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.