In theory due to the op-amps high open-loop gain the magnitude of its output voltage could be infinite in both directions, ( ± ∞). We can also see that the value of the output voltage is completely dependent on the op-amps power supply voltage.

This condition is true regardless of whether the input signal is connected to the inverting or the non-inverting input of the comparator. Then we can see that the op-amp voltage comparator is a device whose output is dependant on the value of the input voltage, V IN with respect to some DC voltage level as the output is HIGH when the voltage on the non-inverting input is greater than the voltage on the inverting input, and LOW when the non-inverting input is less than the inverting input voltage. Then we can say that the voltage comparator is essentially a 1-bit analogue to digital converter, as the input signal is analogue but the output behaves digitally. The open-loop op-amp comparator is an analogue circuit that operates in its non-linear region as changes in the two analogue inputs, V+ and V- causes it to behave like a digital bistable device as triggering causes it to have two possible output states, +Vcc or -Vcc. Then due to this high open loop gain, the output from the comparator swings either fully to its positive supply rail, +Vcc or fully to its negative supply rail, -Vcc on the application of varying input signal which passes some preset threshold value. Voltage comparators on the other hand, either use positive feedback or no feedback at all (open-loop mode) to switch its output between two saturated states, because in the open-loop mode the amplifiers voltage gain is basically equal to A VO.

We have also seen that the standard operational amplifier is characterised by its open-loop gain A O and that its output voltage is given by the expression: V OUT = A O(V+ – V-) where V+ and V- correspond to the voltages at the non-inverting and the inverting terminals respectively. We have seen in previous tutorials that the operational amplifier can be used with negative feedback to control the magnitude of its output signal in the linear region performing a variety of different functions. In other words, the op-amp voltage comparator compares the magnitudes of two voltage inputs and determines which is the largest of the two. The Op-amp comparator compares one analogue voltage level with another analogue voltage level, or some preset reference voltage, V REF and produces an output signal based on this voltage comparison.

Negative feedback op amp