Analog Or Gate?

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas

I have a problem where I would like to pass the greater of two signals, a kind of "analog or". It seems to me that this has come up before, but search fails me. Anybody have a schematic, or even a better keyword?

JingleJoe · Posted: Wed Jun 27, 2012 11:03 am Post subject:

Two diodes should do.
simply make a diode based OR gate, with a pull down resistor on the end, that will pass analogue voltages above the diode voltage.

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas

I'm looking for something a little more sophisticated; the diodes will have a voltage drop and won't pass bipolar signals.

JovianPyx · Posted: Wed Jun 27, 2012 2:51 pm Post subject:

Hmm... A comparator monitors the two voltages. The voltages are then passed through two transmission gates of a 4066 which is controlled by the comparator and the logically inverted output of the comparator. Of course, that puts limitations on the range of voltages it will pass. I.e., you can expect to pass a range of +15 to -15 through a transmission gate. The transmission gates outputs are connected together to form a single output. May need resistors on the xmission gate outs, not sure.

andrewF · Posted: Wed Jun 27, 2012 5:33 pm Post subject:

This is what you need...............maybe
http://electro-music.com/forum/topic-21851.html

brock · Joined: May 26, 2011 Posts: 75 Location: Canada

JovianPyx · Posted: Thu Jun 28, 2012 6:22 am Post subject:

Not sure if it's an "error", more of a memory lapse - I couldn't remember the part number you cited. However, I think that the technique would work, no?

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas

Thanks guys!

The comparator + switch combo sounds like a workable approach. I didn't know about DG403, but looking over the datasheet it does seem more appropriate than the 4066. (For onlookers: the 4066 switches analog signals up to +/-7.5V peak, whereas the DG403 will switch signals up to +/-15V ptp.)

I'll do some experiments along these lines.

brock · Joined: May 26, 2011 Posts: 75 Location: Canada

The concept will work no problem. I think Aries may even have made a module like this in their analog switch which, if I recall correctly, could be controlled with an analog voltage. High probability of memory lapse on my part with that guess/memory though as that's going back a long time.

wmonk · Posted: Sun Jul 01, 2012 2:48 pm Post subject:

There is the YuSynth Min/Max that does this.
Easy to build and a module I love.

http://yusynth.net/Modular/EN/MINMAX/index.html

PHOBoS · Posted: Mon Jul 02, 2012 6:34 am Post subject:

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas

TL071/072/074 should be okay instead of LM324 in the YuSynth circuit, right?

JingleJoe · Posted: Mon Jul 02, 2012 2:29 pm Post subject:

corex · Joined: Mar 02, 2010 Posts: 100 Location: Las Vegas