DECODERS

Decoder is a device that, when activated,  selects one of several output lines based on  coded input signal.Most commonly the input is in n- bit binary number, and there are 2^n output lines. Some decoders have an enable signal that activates it.

Active high decoder is the active output is 1 and the inactive ones are 0 and its truth table has two inputs and four outputs. The inputs are treated as a binary number and the output selected is made. This decoder consist oof an AND gate for each output plus NOT gate to invert the inputs.

                     a.)        an active high decoder                        

An active low output version of the decoder has one 0 corresponding to the input combination, the remaining outputs are 1. The circuit and the truth table describing it in the figure where the AND gates in the active high are just replaced by NANDs.

                b.)          an active low decoder

By: Dinah Rose Y Galiza