EC8453 Linear Integrated Circuits Unit - 2
Unit 2
Applications of Operational Amplifier
1. State the difference between conventional and precision rectifier.
S. Conventional Rectifier Precision Rectifier
No.
1. Practical diode is used Ideal diode constructed by placing diode
in feedback loop of OPAMP
2. Diode conduct 0.7V for Silicon or Diode conduct when
0.3V for Germanium
3. Cross over distortion occurs Cross over distortion is completely
eliminated.
2. Define Bandwidth of a filter
Bandwidth of a filter is defined as the difference between higher cutoff
frequency fH and lower cut fL. And it is given as
BW = fH-fL
Always fH will be greater than fL and these two frequencies are marked at gain
3dB down the maximum gain of filter.
3. What is a voltage follower?
A circuit which the output voltage follows the input voltage is called voltage
follower circuit. That is output voltage is equal to input voltage. This circuit is also
called as OPAMP buffer.
4. Draw the diagram of peak detector.
EC8453 Linear Integrated Circuits Unit - 2
5. Give an application for each of the following circuits: Voltage follower, peak
detector, Schmitt trigger and clamper.
Voltage Follower:
It has high input impedance and low output impedance. So it is used to
eliminate loading effect. Also used as buffer.
Peak Detector:
Used in amplitude modulation as detector and in test and measurement
instrumentation applications.
Schmitt Trigger:
Used in wave shaping circuit to convert any input to square wave output and
act as square wave converter.
Clamper:
Clamper circuit is used to add dc signal to the ac output both in positive and
negative sides. Often it is used in Television.
6. Give an application of an inverting amplifier.
Sign changer is typical application of an inverting amplifier. It is special case
with Rf = R1 and hence Thus we can call it as unity gain inverter.
7. Draw the circuit diagram and write output equation of an OPAMP differentiator
circuit.
8. How does precision rectifier differ from conventional rectifier?
A precision rectifier from ordinary diode rectifier in a way that it can even
rectify input signal voltage less than cut-in voltage of the diode. This is done by
placing a ordinary diode in the feedback path of an OPAMP. Using this arrangement,
rectification is possible for input range even in milli-volt.
EC8453 Linear Integrated Circuits Unit - 2
9. What is Comparator?
A comparator is a circuit which compares the unknown signal voltage applied
at one input of OPAMP with the known signal voltage applied (reference) at the other
input. It is open loop configuration circuit with only two possible output +Vsat and
–Vsat. When the differential voltage Vid is positive, the output will be +Vsat and when
Vid is negative, the output will be –Vsat.
10. Why is integrator preferred over differentiators?
An analog computer can perform linear operations such as multiplication by
constant, addition, subtraction, and integration. These operations are sufficient for
solving linear differential equation. Linear differential equation can also be solved
directly by using differentiator. But, the gain of differentiator increase linearly with
frequency and amplifies noise and drift, resulting in false oscillations. Therefore,
integrators are preferred over differentiators in analog computers.
11. Mention two important features or characteristics of instrumentation amplifier.
i. High gain accuracy
ii. High CMRR
iii. High gain stability
iv. Low DC offset
v. Low output Impedance
vi. High Input Impedance
12. Draw and write equation of an integrator using an OPAMP.
13. Give the schematic of OPAMP based current to voltage converter.
EC8453 Linear Integrated Circuits Unit - 2
14. Give the circuit of a voltage to current opamp converter.
1. V to I Converter with floating load
2.V to I Converter with Grounded Load
15. State the application of comparator.
i. Digital interfacing
ii. Schmitt trigger
iii. Discriminators
iv. Voltage level detectors
v. Oscillators
vi. Time maker generator
vii. Zero crossing detector
viii. Window detector
ix. Phase meter
16. Draw the circuit of log amplifier.
EC8453 Linear Integrated Circuits Unit - 2
17. Draw averaging circuit using operational amplifier
18. What is zero crossing detectors?
Zero crossing detector is one of the application of OPAMP comparator. The
circuit finds the points at which the input voltage cross zero (or) DC level.
19. What is a V to C or V to I converter?
V to C or V to I is the voltage to current converter. In most of measuring
applications, it is sometimes convenient to measure current than voltage. So when the
input is voltage for such applications, is first converted to current with the help of V
to C converter. There are two types
i. With floating load
ii. With grounded load
20. What is an antilog amplifier? Draw the circuit diagram of an antilog amplifier.
A circuit that perform the mathematical operation of antilog is called as
antilog amplifier. It performs the reverse operation of log amplifier. An antilog
amplifier can be constructed either by using a diode or transistor. The following
circuit is antilog amplifier using a diode.
21. What is an OPAMP comparator?
A comparator is a circuit which compares the unknown signal voltage applied
at one input of OPAMP with known reference voltage at the other input of OPAMP.
OPAMP as comparator is a open loop circuit and only two possible output voltages
±Vsat.
22. State the principles of regenerative comparator.
Schmitt trigger is also known as regenerative comparator. This circuit convers
any irregular shaped input wave to square wave. The reference voltage required for
comparison is taken from output voltage through a potential divider (VUT and VLT)
which is compared with input voltage Vin.Vin is applied to inverting terminals and VUT
EC8453 Linear Integrated Circuits Unit - 2
or VLT applied to non inverting terminal of OPAMP. If Vin >VUT, Vo goes to –Vsat and
if –Vin>VLT, Vo goes to +Vsat and the result is a square wave output. Thus Vo switches
from +Vsat to -Vsat and vice versa causing regenerative action.
23. Draw the Schmitt trigger and give its application.
Schmitt trigger is mainly used to convert very slowly varying signals into a fastly
switches square wave signals and often used as a wave shaping circuits.
24. Give the circuit for precision rectifier.
25. State the disadvantage of Passive filters.
1. Gain and frequency adjustment problem
2. Hign cost due to inductors
3. Loading problem arises due to low input impedance and high output impedance.
4. Possible signal attenuation
5. Inductors are bulky and occupies more space and its noisy too.
26. What is hysteresis and mention the purpose of hysteresis in a comparator?
A comparator with positive feedback is said to have a condition called
hysteresis. It is a dead band condition similar to magnetic hysteresis loop. Hysteresis
voltage is the difference between two threshold voltages VUT and VLT of comparator.
The purpose of hysteresis is to understand the regenerative action of
comparator as Schmitt trigger. It tells the relation between input voltage and output
voltage of comparator.
