What is a Digital System

Lets start with basic, ie .digital system. in electronics as you already know only 2 states are used - LOGIC HIGH and LOGIC LOW, represented by 1 and 0 respectively.

GOOGLY- Why assign '0' and '1' and not 'a' and 'b' or 'x' and 'y' or 'cat' and 'dog' etc.
answer- computation ease!
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Types of digital circuits:

Combinational circuits : output depends only on present states.eg logic gates.
Sequential circuits       : next states is completely determined by past states.eg counter and flipflop.

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Clock: building block of sequential circuit

A clock is simply high and low states of voltage with time ie essentially a square wave.

duty cycle: it is ratio of Ton and Toff.

Logic gates :  building block of combinational circuit

these are essentially combinational circuitry used to implement boolean operation like AND OR NOT NAND NOR XOR XNOR etc.

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