The ramp generator or integrator uses a capacitor in the feedback loop of the operational amplifier. The capacitor is connected to the inverting voltage amplifier as shown below.
The output voltage rises steadily as the capacitor charges, until the operational amplifier reaches a saturating voltage a little less than the supply voltage. The variation of
with time is shown below.
is almost zero so the voltage across
will be the input voltage
and the voltage across the capacitor will be the output voltage
Very little current will flow into the inverting input of the op – amp, all the input current flows onto the capacitor, charging it.
The current charging the capacitor is constant, given by
The charge on the capacitor is then
so
Hence
Ifis allowed to vary then
It is this equation that allows the circuit the alternative name of integrator.