multiplexers for implementation of logic gates

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Disha Karnataki

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hey people,
i started reading about multiplexers recently and could not understand implementation of logic gates using mux's. I got to know the methodology the way they have implemented certain functions say Ʃm(1,3,5,7,8,9,12) using 4:1 mux with a,b as select lines.
Here they form k-map and get out some Boolean expression and apply it to data lines or inputs where the Boolean expressions are in form of c,d.
i did not get after this i.e as per my knowledge Ʃm(1,3,5,7,8,9,12) means it's the sop equation and when i am realizing this function i should get out this function as a whole right?? Am i right?? Please help i am unable to understand this point that how exactly is the given sop equation realised......???
 

If i understood what you ask right, then a multiplexor acts like a table.

4:1 mux have 4 input lines, two select lines, and one output.
To make it a gate, you assume the select lines to be the inputs of the gate, the output stays the output, and the 4 input lines would store the table.
So, the input signal on the select lines make the mux produce the output from the corresponding line of the table.

I.e. a XOR function:
Code: 
Input lines values:
0 is 0
1 is 1
2 is 1
3 is 0

Gate:
A B Picked_line Output
0 0       0        0
0 1       1        1
1 0       2        1
1 1       3        0
 

Yes, you get whole sop equation. A and B are select lines. so there are four combinations of A and B viz. 00, 01, 10, 11. There are four inputs to given MUX. You give this four inputs in terms of C and D according to K-map or truth table or whatever method. Then you get output according to given mean-terms. Actually you are selecting these mean-terms i.e. Ʃm(1,3,5,7,8,9,12) using MUX. Got the point?

Best regards
 



You may also encounter "Look Up Table(LUT) implementation of a boolean function". It's almost the same. Assume inputs form address of a ROM, and it's cell programmed to output values from your table.
 

yes i got the point now my question is what are exactly present at the data lines?? i have also read that in telephones use multiplexers but all telephone lines carry analog signals. so at the data lines do we have analog signals??? what is the stuff exactly about these data lines??? what is exactly present at it?? please give indepth overview of it.

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yes i got the point now my question is what are exactly present at the data lines?? i have also read that in telephones use multiplexers but all telephone lines carry analog signals. so at the data lines do we have analog signals??? what is the stuff exactly about these data lines??? what is exactly present at it?? please give indepth overview of it.
 

Maybe that can help:
Simulation of 4 mux doing AND

It's a circuit simulator, with a 4-mux loaded in it doing AND.
Try pressing on A and B and see what happens (click on L/H letters).
Then try to reprogram it by changing values on the inputs, and see what different A and B values would produce.

 
thanks a lot but.. there was one more question i had asked it is as follows:
i have read that telephones use multiplexers but all telephone lines carry analog signals. so at the data lines do we have analog signals???, which continuously vary.
 

A multiplexor is not a device, but a type of a device.
Something that gives on the output what is present on the selected input.

It can be made out of logic gates, producing a digital signal on the output from digital signal on the input.
Or it can be made out of mechanical relays, producing analog signal on the output, or forming electric power current path between the output and the selected input.
Or it can be made out of valves, passing gas from selected input tank to the output hose.

So, if you are talking in terms of making logic gates out of a mux, then you're likely talking about a digital one.
 

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