The Op-amp comparator compares one analog voltage level
with another analog voltage level, or some preset reference
voltage, VREF and produces an output signal based on this voltage
comparison.
OPAMP VOLTAGE COMPARATOR
The Op-amp comparator compares one analogue voltage level
with another analogue voltage level, or some preset reference
voltage, VREF and produces an output signal based on this voltage
comparison.
Thus, the op-amp voltage comparator compares the magnitudes
of two voltage inputs and determines which is the largest of the
two.
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 AVO.
1
, ctd
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.
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 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.
2
, op-amp voltage comparator circuit
3
, ctd
With reference to the op-amp comparator circuit in the fig above
first assume that VIN is less than the DC voltage level at VREF,
(VIN < VREF ).
As the non-inverting (positive) input of the comparator is less than
the inverting (negative) input, the output will be LOW and at the
negative supply voltage, -Vcc resulting in a negative saturation of
the output.
If the input voltage(Vin) is increased so that its value is greater
than the reference voltage VREF on the inverting input, the output
voltage rapidly switches HIGH towards the positive supply
voltage, +Vcc resulting in a positive saturation of the output.
4
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