Astable multivibrator using opamp and using logic gates with working principle ,circuit diagram and its characteristics

Astable multivibrator using operational amplifier :-

Op-amp are also known as operational amplifier.

It has very high gain DC amplifier and is used in generation of waveform like a square and triangular wave etc.

Block diagram and symbol of operation amplifier 

It has two input labelled as negative and positive known as inverting and non inverting respectively.

Astable multivibrator using operational amplifier 

Input V1 is applied between ground and inverting input.  V2 is applied between ground and non inverting terminal. The output voltage Vo is available between ground and output. The input terminal are referred as differential input and output is the single ended. The output voltage depends upon the difference of input voltage.

Vi= V1-V2

V0 = Av.Vi

                  Where Av =voltage gain 

An opamp based astable multivibrator is a square wave generator which is shown above.

• Whenever potential of P becomes less than that of Q the output of op- amp Vo and whenever it becomes more the output Vo goes low.
• For Vo high (positive) ,Q is at positive voltage equal to βvo[β=R3/(R3+R4)] , capacitor charges positively through resistance R1. When the potential point P crosses that of Q, the output b0 suddenly swing to negative value(-Vo) i.e low output. And the voltage at Q becomes -βVo .
• Now the capacitor start charging and then charging in opposite direction i.e from ground to R1.
• The the voltage at P gradually turns negative. When P becomes more negative than Q the output voltage Vo suddenly swings to positive and the capacitor start charging.

Astable multivibrator using logic gates :-

Block diagram of astable multivibrator using logic gates 

Waveform of multivibrator 

Astable multivibrator can be designed by directly feeding back output of a NOT GATE. The circuit works on the same principle of RC phase shift oscillator.
The phase shift is provided by the propagation delay time of the interval and the frequency of oscillation depends upon propagation delay of the gate.