What are the Basic Building Blocks of a Digital Circuit

The basic building blocks of a digital circuit are ‘logic gates’. Logic gates are electronic circuits made by using various active and passive elements in different combinations for the implementation of certain logics. The three fundamental logic gates in digital electronics are:-

AND gate OR gate NOT gate

An AND gate is a multiple input/single output gate in which the output is true only if all the inputs are true, otherwise it is false. An OR gate is a multiple input/single output gate in which the output is true when at least one of the inputs is true. If all the inputs are false, only then the output of the gate becomes false. The third and final fundamental gate i.e. NOT gate is a single input/single output gate in which the output is the compliment of the input which means that the output is true if the input is false and the output is false if the input is true.

Then a question arises as to why these are known as the fundamental logic gates? Any digital circuit, no matter how much complicated can always be synthesized using the AND, OR and NOT gates in various circuit combinations. From a personal computer to a traffic light controller, anything that is digital in this world today can be made by the use of just these three gates.

The problem with synthesizing complex digital systems just with the use of the above mentioned three gates is that such a system is not optimum when it comes to factors like:-

Cost of the circuit Energy and Power Consumption Size of the circuit Speed and other Performance Characteristics

To overcome this drawback, other higher level digital building blocks are used by designers for synthesizing complex digital electronic circuits. The use of universal gates such as NAND or NOR for designing improves many characteristics of complex digital circuits as compared to a circuit just made by using the three fundamental gates.

Today in the market many IC’s of various digital blocks like counters, flip-flops, registers, ADC’s, DAC’s etc are present that are used by designers. This makes the synthesis of complex digital circuits much easier and cost effective, rather than having to make the whole circuitry from the gate level itself. But even in these digital blocks, gates are the basic design units and therefore remain the fundamental building blocks of any digital circuit. The advantage therefore lies in the use of digital block itself as a whole rather than synthesizing it by using various gates.