307_FM

This noninverting integrator uses a Howland current source, an operational amplifier voltage-controlled current source. When a capacitor is used as the load of a VCIS, the circuit functions as an integrator. In the circuit shown a DC source is used as the controlling variable resulting in a constant current output. Therefore the output voltage is a linear ramp. A probe is setup to display both the voltage and current in the integration capacitor. In real applications, its better to get the output voltage from the output terminal of the operational amplifier so that node is also probed. For this example, the voltage at the output of the op-amp is twice the voltage at the integration capacitor. The output of the VCIS is Iout = 5 V / 5 kOhms Iout = 1 mA Therefore the capacitor voltage has a slope of 1 mA / 1 uF = 1 V / mSec and the output voltage of the op-amp has a slope of 2 V / mSec.