Today we are present in a digital world where almost all electronics are now digital i.e Digital clock,calculator etc. All the electronics depend on signals. Any thing which varies with respect to time is called signal or one axis must time. There are two types of signals

1)Continuous Time Signal: specified for every value of time

2)Discrete Time Signal:it is logic 1 for specified value else 0.

Digital signal have two specified value. When 1 is higher than 0 then it is +ve logic i.e 1V –> 5V.

It’s inverse is -ve logic i.e 1V –> -5V. Any method that produce 2 states (0,1) called digital method.

1–10 gates                     Small Scale Integration

10–100 gates                 Medium Scale Integration

100–10000  gates          Large Scale Integration

10000–million  gates      Very Large Scale Integration

1)Power Consumption

In electrical engineering power consumption refers to energy per unit time. Power consumption usually measures in Watts or kiloWatts.

2)Fan out

number of inputs that can connected to specified output or maximum similar gates connected to each other. TTL gate has fan out of 10.

3)propagation delay

in electronics propagation delay means time consumed in transfer of signal from sender to receiver.

4)noise margin

when signal exceeds the threshold a proper 0 or 1.


Analog                                                            Digital


Continuous wave that changes                                                    Discrete wave that carry informat-

with time                                                                                       ion in binary form.


Sine wave                           Square wave


Described  amplitude,frequency                Described by bit rate,bit interval


No fix range                        Finite range


Prone to noise                        Less prone


                                       human voice                   signals used for transmission in computer

Note:Decrease in amplitude of a signal is called attanuation.


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