An integrator is a circuit which shows the sum of input voltage at the output. That means it works by the operation of integral form. If we see the output of the integrator shows the summation of input voltages, the result of integrator circuit will be right. Such that, if we give square wave at the input, then we will get triangular wave at the output.
A circuit in which the output voltage waveform of Op amp is the integral of the input voltage waveform is the integrator or the integrator amplifier. Such a circuit is obtained by using a basic inverting amplifier configuration if the feedback resistor RF is replaced by a capacitor CF.
Integrators are used in the design of signal generators and signal processing circuits. It is also used in analog computers and analog-to-digital (ADC) and signal-wave shaping circuits.
When Vin = 0, the integrator of Fig 1(a) works as an open-loop amplifier. This is because the capacitor CF acts as an open circuit (XCF = ∞) to the input offset voltage Vio. In other words, the input offset voltage Vio and the part of the input current charging capacitor CF produce the error voltage at the output of the integrator.
Therefore, in the practical integrator to reduce the error voltage at the output, a resistor RF is connected across the feedback capacitor CF. Thus, RF limits the low-frequency gain and hence minimizes the variations in the output voltage.
Both the stability and the low-frequency roll-off problems can be created in ideal integrator. Those problems can be corrected by the addition of a resistor RF. From the simulation result, we can see that the output of square wave is the triangular wave. So, we can say that integrator does the sum at the output.