Re: [sdiy] an XOR question

[Roman]

I think a parity tree IS multiple input XOR. What you're trying to achieve with the big circuit is to have a "1" only when one of 4 inputs is high, right?
How about analog solution. Inputs mixer made of 4 equal resistors, their common node goes to (-) of LM311. (+) of 311 is set to about 3/8 of supply voltage. Then 4 diodes go from 4 inputs (andoes) to one resistor, that would be pull-up of 311's open collector output.
If all inputs are 0, 311 output is also 0, because there's no pull-up supply. If one input is high, voltage at (-) of 311 is 1/4 of power supply, still below threshold, and the comparator has already pull-up supply and goes high. If more than 1 input goes high, voltage at (-) is at least 1/2 of supply voltage, and comparator goes low.

This is only my sick idea, and has very long propagation time even comparing to CMOS logic.

Roman

---- Wiadomość Oryginalna ----
Od: "Schierl, Dan" 
Do: synth-diy at dropmix.xs4all.nl
Data: Sat, 11 Sep 2004 17:22:24 -0500
Temat: [sdiy] an XOR question


Hi list--
I have an application I'm working on in which I need to perform an exclusive OR on 4 inputs. Since I don't think anyone makes a 4-input XOR, I tried to rig something up using some CMOS chips. My first attempt was a little too simplistic (i.e. wrong), which I didn't realize until I'd already wired it into my application. I think my second attempt works (haven't tried it yet, tho) but i think it might be overkill. 

Go here: http://people.msoe.edu/~schierld/temp/xor.html to see my two ideas.

My question is: the second idea is pretty much a literal definition of an XOR gate, but I wonder if there are any trick ways to make one of these with fewer chips. Any thoughts you might have would be appreciated. thanks!