Actually you can not bother to design a multiplexer using logic gates because it has many special IC which functioned for a multiplexer. One of the TTL ICs from the family that you can use to fulfill the function of a multiplexer is IC 74 251. At the IC there are 8 input channels and 3-bit selector and the other lane as a control reset and inverting output. As a note if you are using TTL ICs for your electronic circuit, the voltage supply that is allowed a maximum of 5 volts. So you can be more familiar with the workings of this multiplexer ic, IC74251 consider the truth table below: C B A G Y W X X X 1 Z Z 0 0 0 0 D0 D0’ 0 0 1 0 D1 D1’ 0 1 0 0 D2 D2’ 0 1 1 0 D3 D3’ 1 0 0 0 D4 D4’ 1 0 1 0 D5 D5’ 1 1 0 0 D6 D6’ 1 1 1 0 D7 D7’ Z = High impedance (off) D0,D1…D7 = Representing the output of the input lines D