circuit-fantasia > circuit stories > building circuits > Op-amp RC integrator (short)

Building Circuits on the Whiteboard

Op-amp RC Integrator (short version)

As the inverting input of the op-amp is at virtual ground (0 V) the input current is constant and determined only by the input voltage VIN and the resistor R. The output voltage Vout is a copy of the voltage across the capacitor C.

If we drive a capacitor by a constant current source, it functions as an ideal current-to-voltage integrator. Click to view full-size picture.

If you drive a capacitor by a constant current source, it functions as an ideal current-to-voltage integrator.

In order to build an integrator with voltage input, connect a voltage-to-current converter before the circuit.

Only, the voltage drop VC across the capacitor C affects the input current and the output voltage changes exponentially trough the time.

Only, the voltage drop VC across the capacitor C affects the input current and the output voltage changes exponentially trough the time.

In order to help the input voltage source, connect an additional supplementary battery BS and adjust its voltage so that VS = -VC.

In order to help the input voltage source, connect an additional battery BS and adjust its voltage so that VS = -VC. Click to view full-size picture.

Finally, replace the "manual" op-amp with a real one; then use its compensating voltage as an output of the integrator.

Finally, replace the 'manual' op-amp with a real one and use its compensating voltage as an output of the integrator. Click to view full-size picture.

Finally, remove all the "unnecessary" components of the picture to get the classic circuit diagram of the op-amp integrator:).

Now, you may place this simple but nonunderstandable diagram at any recipe book on electronics:).

circuit-fantasia > circuit stories > building circuits > Op-amp RC integrator (short)