De-Multiplexers

A De-multiplexer (De-Mux) can be described as a combinational circuit that performs the reverse operation of a Multiplexer.

The following image shows the block diagram of a 1 * 4 De-multiplexer.

The function table for a 1 * 4 De - Multiplexer can be represented as:

From the above function table, we can write the Boolean function for each output as:

y3 = S1S0 I, y2 = S1S0' I, y1 = S1' S0 I, y0 = S1'S0' I

The above equations can be implemented using inverters and three-input AND gates.

We can also implement higher order De-multiplexers using lower order De-multiplexers. For instance, let us implement a 1 * 8 De-multiplexer using 1 * 2 De-multiplexer in the first stage followed by two 1 * 4 De-multiplexers in the second stage.

The function table for a 1 * 8 De-multiplexer can be represented as:

The block diagram for a 1 * 8 De-multiplexer can be represented as:

The Selection lines 'S1' and 'S0' are common for both of the 1 * 4 De-multiplexers.