Details about Integrator, Differentiator and Scale Changer

Integrator

The circuit diagram of integrator using operational amplifier is shown in the below fig. This circuit is same as inverting amplifier except that the capacitor C is placed in the place of feedback resistor. The input current to the ideal amplifier is zero. The feedback through the capacitor C forces a virtual ground to exist at the inverting input terminal. Thus the voltage across C is simply the output voltage.

Pic 1 Integrator

The amplifiers therefore, provides an output signal which is proportional to the integral of the input voltage.
Differentiator
The circuit diagram of differentiation using operational amplifier is shown in the below fig. In this circuit the capacitor C and resistor R of the integrator are interchanged. Because of the virtual ground at the inverting terminal, the current I1 in the fig.
Pic 2 Differentiator 

The output voltage i.e. voltage across resistor R can be expressed as
                                 VO = -RI1

Thus, the above circuit provides an output signal which is proportional to the derivative of the input voltage
Scale changer
The multiplier circuit using an operational amplifier is shown in the below fig. this is an inverting amplifier. Here feedback resistor value Vf = nR1. From the analysis of inverting amplifier, the output voltage is given as
VO = - nR1/R1 . Vin
Therefore   VO = - n Vin
Pic 3 scale changer

Thus the output voltage is n times that of input. The sign can be changed by using another op-amp sign changer in cascade.

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