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# CMOS LOGIC

#### Krishna_27

##### Newbie
How to implement 3 input exor function using cmos?

In there study how NOT, AND and OR gates are built.
Using the same principles, build a 3 input EXOR function. It is not complicated.

can you supply the required truth table for this please?

i.e. all inputs high = o/p low

but for 2 inputs high - what is the desired output ?

for one input high ?

This was in an engineering quiz I remember from about 40 years ago. Lots of clever digital design people sat around a table and decided it was impossible. XOR (EXOR) is only possible with two inputs but you can of course combine any number of signals prior to them becoming one of the inputs.

Brian.

xor or exor : meaning of it is that the output should be a 1 if and only if exactly one of the inputs is a 1. For a 3 input function, this needs to be preserved.
A simple way to implement it in CMOS would be to use a cascade of 2-input gates.

Lots of clever digital design people sat around a table and decided it was impossible. XOR (EXOR) is only possible with two inputs
Apparently Texas Instruments wasn't there, they later made three input XOR gate 74LVC1G386. XOR can be extended to any number of inputs, the output is 1 for odd number of active inputs.

Doesn't that make it a parity generator ?

Brian.

Yes, parity generator