Analog Electronics Basic Op-Amp Applications - LIGO

5.6. ANALOG COMPARATOR 117
D 0
v C
v i
A
D 1
R
−
+
−
+
A
v o
C 0
RESET
Figure 5.11: Peak detector circuit.
5.6 Analog Comparator
An analog comparator or simply comparator is a circuit with two inputs v i ,
v re f and one output v o which fulfills the following characteristic:
{
V1 , v
v o =
i > v re f
V 2 , v i ≤ v re f
An Op-Amp with no feedback behaves like a comparator. In fact, if we
apply a voltage v i > v re f , then V + − V − = v i − v re f > 0. Because of the
high gain, the Op-Amp will set v o to its maximum value +V sat which is a
value close to the positive voltage of the power supply. If v i < v re f , then
v o = −V sat . The magnitude of the saturation voltage are typically about
1V less than the supplies voltages.
Depending on which input we use as voltage reference v re f , the Opamp
can be an inverting or a non inverting analog comparator.
It is worthwhile to notice that the analog comparator circuit is also a 1
bit analog digital converter , which converts voltages to the two levels V 1
and V 2 .
DRAFT