The document discusses the operational amplifier (op-amp) IC 741, explaining its function in performing mathematical operations and amplifying signals. It details the internal structure, ideal characteristics, limitations of open-loop configurations, and the necessity of negative feedback for linear applications. The summary includes practical applications such as inverting and non-inverting configurations and the concept of virtual ground.

1. Operational Amplifier
IC 741

2. Operational Amplifier
An op-amp is an electronic circuit that could carry out mathematical
operations of addition, subtraction, differentiation and integration.
Op-amp is used to amplify DC and AC signals.
2

3. Block Diagram of Operational
Amplifier
Differential
Amplifier
Differential
Amplifier
Buffer &
Level
Translator
Output
Driver
3
V2
V1
Vo

4. Block Diagram of Operational
Amplifier
Differential Amplifier:
First two stages are cascaded differential amplifiers used to provide
high gain and high input impedance
Buffer:
Emitter follower whose input impedance is very high so that it
prevents loading of high gain stage
Level Translator:
It adjust d.c. voltages so that the output voltage is zero for Zero
inputs
Output Stage:
Used to provide low impedance as demanded by the ideal op amp
characteristics
4

6. Active component!
Introduction
Basic Symbol

8. Operational Amplifier – Ideal
Characteristics
Voltage Gain = Infinite (Very large gain at very low frequency; Thus
small changes in voltages can be amplified by using an op amp).
Infinite Input Impedance.
Low Output Impedance.
Infinite Bandwidth
8

9. Equivalent circuit of Practical OP.Amp

10. Ideal vs typical op amp
Ideal Op-Amp Typical Op-Amp
Input Resistance infinity 106  (bipolar)
109  - 1012  (FET)
Input Current 0 10-12 – 10-8 A
Output Resistance 0 100 – 1000 
Operational Gain infinity 105 - 109
Common Mode Gain 0 10-5
Bandwidth infinity Attenuates and phases at high
frequencies (depends on slew
rate)
Temperature independent Bandwidth and gain

11. Relationship between Vo and difference of i/p
voltage ideal op amp
V0 α difference of i/p voltage
V0 α (V+ - V-)

12. +Vsat
-Vsat

13. Open loop operation of Practical Op Amp
• Open loop gain high
• A ~= 106
• Small difference in the input
voltages result in a very large
output voltage
• Output limited by supply voltages
• Comparator
• If V+>V-, Vout = HVS (+15V)
• If V+<V-, Vout = LVS (-15V)
• If V+=V-, Vout = 0V

14. Limitations of Open Loop
Configuration in Operational
Amplifier
Distortion is introduced in the amplified output signal.
Open loop gain does not remains constant but varies with respect to
temperature and power supply.
Bandwidth of Op-amp is very small and almost equal to zero and it
makes it insufficient for practical use.
Applications:
Comparator
14

15. Need of negative feedback in op-amp
• Any input signal slightly greater than zero drive the output to
saturation level because of very high gain (AOL= ∞).
• Thus when operated in open-loop, the output of the OPAMP is either
negative or positive saturation or switches between positive and
negative saturation levels (comparator). Therefore open loop op-amp
is not used in linear applications.

16. Need of negative feedback in op-amp
• With negative feedback, the voltage gain (ACL) can be reduced and
controlled so that op-amp can function as a linear amplifier.
• The op-amp with negative feedback forces the
two Inputs v+ and v- to have the same voltage,
If v+ is held at 0 volt, then v- will be forced to 0 volts.
This zeo volt forced at –ve input is called “virtual ground”.

17. Basic Applications circuits
• Inverting op amp
• Non-inverting op amp
• Voltage follower