Operational Amplifier OpAmpA 741 Opamp is a Linear

Operational Amplifier (Op-Amp)-μA 741 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. 1 Notch 74 1

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 180 o out-of-phase (or opposite polarity) signal at 2 the output.

COMPARISON BETWEEN CHARACTERISTICS OF AN IDEAL AND REAL OP-AMP (μA 741) Parameters Ideal Real Open Loop Gain A ∞ 105 Input Impedance Ri ∞ 2 MΩ Output Impedance Ro 0 75 Ω 3

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

Virtual Short So, (1) The voltage between V+ and V is zero V+ = V As V 1 and V 2 are not shorted but are at equal potential, therefore called virtual short. (2) The current into both V+ and V terminals is zero. I+ = 0 ; I- = 0 5

Inverting Amplifier If RF = Rin, Vout = - Vin Non-Inverting Amplifier Due to virtual short Vin = V 1 6

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

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 1 MΩ as it is equal to that of the operational amplifiers input impedance. 8

IF Integrator V 2 = 0 Integrator Circuit +1 V -1 V 9

Differentiator V 2 = 0 Differentiator Circuit 10

Summing Amplifier 11

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

Difference Amplifier Va Due to virtual short Va = Vb Vb Difference Amplifier Circuit When R 1 = R 3 and R 2 = R 4 the transfer function becomes: If R 1 = R 2, then Thus the amplifier becomes a Unity Gain Differential Amplifier. 13