1. Operational Amplifier (Op-Amp)-μA741
Op-amp is a Linear Integrated Circuit used to amplify dc as well as ac signals and to perform mathematical operations such as addition, subtraction, integration and differentiation.
The input-output relationship of the op-amp is Vo = A (Vn – Vi)
where, A is the open loop gain of the op-amp.
741
Notch 1 1

2. Op-Amp Schematic Symbol
Op-Amp (contd…) A
Op-Amp Schematic Symbol
741 Op-Amp Pin Diagram
An ac signal (or dc voltage) applied to the non-inverting terminal produces an in-phase (or same polarity) signal at the output.
An ac signal (or dc voltage) applied to the inverting terminal produces an 180o out-of-phase (or opposite polarity) signal at the output. 2 2

3. COMPARISON BETWEEN CHARACTERISTICS OF AN IDEAL AND REAL OP-AMP (μA741)
Parameters
Ideal
Real
Open Loop Gain A ∞
105
Input Impedance Ri
2 MΩ
Output Impedance Ro
75 Ω 3

4. Equivalent Circuit of an Op-Amp
Vo = A(v+ - v-)
The output voltage is directly proportional to the algebraic difference between the two input voltages. vo
Voltage Gain (A) of the Amplifier
where Vin=V+ – V- 4 4

5. Virtual Short
So,
The voltage between V+ and V is zero V+ = V
The current into both V+ and V terminals is zero.
I+ = 0 ; I- = 0
As V1 and V2 are not shorted but are at equal potential, therefore called virtual short. 5

6. Non-Inverting Amplifier
If RF = Rin, Vout = - Vin
Non-Inverting Amplifier
Due to virtual short Vin = V1 6

7. Solution: Solution: Example
Find the closed loop gain of the following inverting amplifier circuit.
Solution:
Example
If Rin is 10kΩ, what value of Rf is required to produce a non-inverting amplifier with voltage gain of 25?
Solution: 7

8. Voltage Follower (Unity Gain Buffer)
In non-inverting amplifier if we make the feedback resistor, Rf = 0 then the circuit will have a fixed gain of "1" and is called a Voltage Follower.
As the input signal is connected directly to the non-inverting input of the amplifier the output signal is not inverted resulting in the output voltage being equal to the input voltage
Vout = Vin
The input impedance of the voltage follower circuit is very high, typically above 1MΩ as it is equal to that of the operational amplifiers input impedance. 8

9. Integrator
V2 = 0 IF
Integrator Circuit
+1V
-1V 9

10. V2 = 0
Differentiator
Differentiator Circuit 10

11. Summing Amplifier
Summing Amplifier 11

12. Example: Find the output voltage of the following Summing Amplifier circuit.12

13. Difference Amplifier Due to virtual short Va = Vb Va Vb
Difference Amplifier Circuit
Difference Amplifier
Due to virtual short Va = Vb
When R1 = R3 and R2 = R4 the transfer function becomes:
If R1 = R2, then
Thus the amplifier becomes a Unity Gain Differential Amplifier. 13