Introduction to Operational Amplifier.pptx

Introduction about operational amplifier

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 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

5. Active component! Introduction Basic Symbol

6. 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

7. Equivalent circuit of Practical OP.Amp

8. Ideal vs typical op amp Ideal Op-Amp Typical Op-Amp Input Resistance infinity 10 6  (bipolar) 10 9  - 10 12  (FET) Input Current 10 -12 – 10 -8 A Output Resistance 100 – 1000  Operational Gain infinity 10 5 - 10 9 Common Mode Gain 10 -5 Bandwidth infinity Attenuates and phases at high frequencies (depends on slew rate) Temperature independent Bandwidth and gain

9. Relationship between V o and difference of i /p voltage ideal op amp V α difference of i /p voltage V α (V + - V - )

10. + V sat - V sat

11. Open loop operation of Practical Op Amp Open loop gain high A ~= 10 6 Small difference in the input voltages result in a very large output voltage Output limited by supply voltages Comparator If V + >V - , V out = HVS (+15V) If V + <V - , V out = LVS (-15V) If V + =V - , V out = 0V

12. 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

13. 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 (A OL = ∞). 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.

14. Need of negative feedback in op-amp With negative feedback, the voltage gain (A CL ) 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 ”.

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