OPERATIONAL AMPLIFIERS
1. If the input to the circuit of figure is a sine wave the output will be
i/p -
o/p
+
a. A half wave rectified sine wave
b. A full-wave rectified sine wave
c. A triangular wave
d. A square wave
[GATE-1990: 2 Marks]
Ans. (d)
Explanation: - The op-amp is in open-loop so it will work as comparator. The
circuit shown here is a zero crossing detector a special case of comparator. When
the input is above ground level, the output is saturated at its negative maximum
and when the input is below ground, the output is at its positive maximum.
2. An Op – Amp has offset voltage of 1mV and is ideal in all other respects. If this Op –
Amp is used in the circuit shown in figure. The output voltage will be (Select the
nearest value)
1MΩ
1KΩ
-
+ V0
a. 1 mV c. ± 1V
b. 1V d. 0V
[GATE-1992: 2 Marks]
, Ans. (c)
Explanation: -
−
= =− =−
Vis = Voffset = 1 mV
V0 = Vis . Gain
= -1 . 10-3 . 103
=-1V
It may be ± 1V (since the polarity of offset voltage is not know)
3. The circuit shown in the figure is that of
Vin -
V0
+
R2
R1
a. a non-inverting Amplifiers c. an oscillator
b. an inverting Amplifiers d. a Schmitt trigger
[GATE-1996: 1 Mark]
Ans. (d)
Explanation: - The circuit has a positive feedback and in positive feedback, op-
amp operates in its saturation region. It is a fast operating voltage level detector.
The circuit switches between negative and positive output voltage levels (- Vsat to
Vsat). It is Schmitt trigger circuit.
4. One input terminal of high gain comparator circuit is connected to ground and a
sinusoidal voltage is applied to the other input. The output of comparator will be
1. If the input to the circuit of figure is a sine wave the output will be
i/p -
o/p
+
a. A half wave rectified sine wave
b. A full-wave rectified sine wave
c. A triangular wave
d. A square wave
[GATE-1990: 2 Marks]
Ans. (d)
Explanation: - The op-amp is in open-loop so it will work as comparator. The
circuit shown here is a zero crossing detector a special case of comparator. When
the input is above ground level, the output is saturated at its negative maximum
and when the input is below ground, the output is at its positive maximum.
2. An Op – Amp has offset voltage of 1mV and is ideal in all other respects. If this Op –
Amp is used in the circuit shown in figure. The output voltage will be (Select the
nearest value)
1MΩ
1KΩ
-
+ V0
a. 1 mV c. ± 1V
b. 1V d. 0V
[GATE-1992: 2 Marks]
, Ans. (c)
Explanation: -
−
= =− =−
Vis = Voffset = 1 mV
V0 = Vis . Gain
= -1 . 10-3 . 103
=-1V
It may be ± 1V (since the polarity of offset voltage is not know)
3. The circuit shown in the figure is that of
Vin -
V0
+
R2
R1
a. a non-inverting Amplifiers c. an oscillator
b. an inverting Amplifiers d. a Schmitt trigger
[GATE-1996: 1 Mark]
Ans. (d)
Explanation: - The circuit has a positive feedback and in positive feedback, op-
amp operates in its saturation region. It is a fast operating voltage level detector.
The circuit switches between negative and positive output voltage levels (- Vsat to
Vsat). It is Schmitt trigger circuit.
4. One input terminal of high gain comparator circuit is connected to ground and a
sinusoidal voltage is applied to the other input. The output of comparator will be
