Prerequisite- Binary Decoder, Multiplexers
A Decoder is a combinational circuit that converts binary information from
Decoder as a De-Multiplexer –
A Decoder with Enable input can function as a demultiplexer. A demultiplexer is a circuit that receives information from a single line and directs it to one of
A
Making 1:4 demultiplexer using 2:4 Decoder with Enable input. Let A, B be the selection lines and EN be the input line for the demultiplexer.
The decoder shown below functions as a 2:4 demultiplexer when EN is taken as a data input line and A and B are taken as the selection inputs. The single input variable E has a path to all four outputs, but the input information is directed to only one of the output lines, as specified by the binary combination of the two selection lines A and B. This can be verified from the truth table of the circuit.
Truth Table-
Combinational Logic Implementation using Decoder –
A decoder takes
Since any boolean function can be expressed as a sum of minterms, a decoder that can generate these minterms along with external OR gates that form their logical sums, can be used to form a circuit of any boolean function.
For example, if we need to implement the logic of a full adder, we need a 3:8 decoder and OR gates. The input to the full adder, first and second bits and carry bit, are used as input to the decoder. Let x, y and z represent these three bits. Sum and Carry outputs of a full adder have the following truth tables-
Therefore we have-
The following circuit diagram shows the implementation of Full adder using a 3:8 Decoder and OR gates.
Advantages and Disadvantages of Combinational circuits using Decoder:
Advantages of Combinational circuits using Decoder:
1.Simplification: Combinational circuits utilizing Decoder can improve on the plan of complicated advanced circuits by diminishing the quantity of information sources required and the intricacy of the rationale capabilities.
2.Flexibility: Combinational circuits utilizing Decoder can be utilized in a large number of utilizations since they can change over paired codes into one-hot codes that can be utilized to control other circuit parts like multiplexers, demultiplexers, or memory gadgets.
3.Modularity: Combinational circuits utilizing Decoder can be effectively scaled and coordinated into bigger computerized frameworks since they are secluded and can be flowed to make more perplexing circuits.
4.Reliability: Combinational circuits utilizing Decoder are dependable and have a low likelihood of failing since they are made out of straightforward, surely knew parts.
Disadvantages of Combinational circuits using Decoder:
1.Complexity: Combinational circuits utilizing Decoder can be complicated and require cautious plan to guarantee that the rationale capabilities are accurately executed and that there are no race conditions or errors.
2.Delay: Combinational circuits utilizing Decoder can bring delay into the circuit since the Decoder expects time to change over the information code into the one-hot result code.
3.Power utilization: Combinational circuits utilizing Decoder can consume more power than different sorts of circuits since they require various parts to carry out the rationale capabilities.
4.Limited adaptability: Combinational circuits utilizing Decoder are restricted to changing over parallel codes into one-hot codes, which can be a detriment in applications that require more mind boggling rationale works or backing for different kinds of codes.
References-
Digital Design, 5th edition by Morris Mano and Michael Ciletti