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Operational Amplifiers

Lecture (11). Operational Amplifiers. Integrated Circuits. What does an AMPLIFIER do?. What is an IC?. OP-Amp is an amplifier IC. Inside an IC. What can you do with Op amps?. You can make music louder when they are used in stereo equipment.

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Operational Amplifiers

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  1. Lecture (11) Operational Amplifiers

  2. Integrated Circuits • What does an AMPLIFIER do? • What is an IC? OP-Amp is an amplifier IC Inside an IC

  3. What can you do with Op amps? • You can make music louder when they are used in stereo equipment. • You can amplify the heartbeat by using them in medical cardiographs. • You can use them as comparators in heating systems. • You can use them for Math operations like summing, integration etc.

  4. OP-AMP (operational amplifier) • An OP-AMP is an integrated circuit (IC) used for amplification of signals. • It is the most widely used analog IC. • It is used in control systems, instrumentation, signal processing etc. • The Operational Amplifier or "op-amp" is an amplifier with two inputs and one output. One input is the inverting input and the other is a non inverting input.

  5. Inverting Input (- VIN) + V Output Differential Amplifier Voltage Amplifier Output Amplifier Noninverting Input (+ VIN) - V Figure 1 Op Amp Block Diagram OP-AMP BLOCK DIAGRAM

  6. OP-AMP HAS 3 –STAGE AMPLIFIER CIRCUITS • First Stage : Differential Amplifier -it gives the OP-AMP high input impedance (resistance) • Second Stage: Voltage Amplifier – it gives high gain • Third Stage : Output Amplifier (Emitter Follower) – gives low output impedance (resistance)

  7. OP-AMP CHARACTERISTICS • Very high input impedance • Very high gain • Very low output impedance OP-AMP is a differential, voltage amplifier with high gain.

  8. OP-AMP is a differential, voltage amplifier with high gain. Why???? • Differential Amplifier: Because it amplifies the difference between 2 voltages • Voltage Amplifier: Because input and output are voltages • High Gain Amplifier: Because the voltage gain is very high (> 100,000)

  9. (a) Op Amp 741 8-pins DIP package (b) OPA547FKTWT DIP SMT package (c) TO-5 metal can 8-Leads package Figure : Op Amp packages The 741 Op-amp The most common op-amp is the 741 IC. Packaging Types

  10. 741 1 1 8 8 +VCC +VCC - - 2 7 2 7 3 6 3 6 + + -VEE -VEE 4 5 4 5 b) Notched Package a) Dot marked Package Figure 3 Op Amp pins Identification OP-AMP pins identification

  11. 1 8. N / C 8 1. Offset Null 741 7. +VCC 2. Inverting Input –VIN 2 7 3 6 6.Output 3. Noninverting Input +VIN 5.Offset Null -VEE 4 5 Figure 4 Op Amp pins Description What are these pins? http://www.quia.com/pp/200743.html

  12. What are these pins? • Pin 1 and Pin 5 : Offset null input, are used to remove the Offset voltage. • Pin 2: Inverting input (-VIN), signals at this pin will be inverted at output Pin 6. • Pin 3: Non-inverting input (+VIN), signals at pin 3 will be processed without inversion. • Pin 4: Negative power supply terminal (-VEE). • Pin 6: Output (VOUT) of the Op-Amp • Pin 7: Positive power supply terminal (+VCC) • Pin 8: No connection (N\C), it is just there to make it a standard 8-pin

  13. +VS -VIN - -VIN VOUT - VOUT +VIN + +VIN + -VS (a) Without power connection (b) With power connection Figure 5 Op Amp Schematic Symbols Symbol of OP-AMP

  14. +VS -VIN - 7 VOUT +VIN 4 + Common Ground -VS Figure 6 Dual Supply Voltages connection Most Op Amps require dual power supply with common ground Positive Supply (+15V) to pin7 Negative Supply (-15V) to pin4

  15. +VS -VIN - 7 VOUT +VIN 4 + -VIN - VOUT 7 +VIN 4 + -VS (a) Single Positive Voltage (b) Single Negative Voltage Figure 7 Single Supply Voltages connection Some Op Amps work on single supply also

  16. +15V +30V 30 V 30 V Output Output 0V -15V 0V Figure 8a Op Amp powered from Dual supply Figure 8b Op Amp powered from Single supply Advantage of dual power supply Using dual power supply will let the op amp to output true AC voltage.

  17. –15V +15V Common Figure 18 Dual Power Supply Single Power Supply Single Power Supply What is dual power supply?

  18. How can you make a dual power supply using two 9V batteries? What is the voltage between + of first battery and – of second battery?

  19. (a) No Feedback (open loop comparator circuit) (b) Negative Feedback (c) Positive Feedback Figure Types of Feedback OP-AMP CONFIGURATIONS

  20. Feedback • No feedback : Open loop (used in comparators) • Negative feedback : Feedback to the inverting input (Used in amplifiers) • Positive feedback : Feedback to the non inverting input (Used in oscillators(

  21. +VS –VIN VO +VIN –VS VO +VS +VIN –VIN 0 +VIN = –VIN +VIN –VIN –VS (a) Comparator Circuit (b) Comparator Output OP AMP as a Comparator (compares 2 voltages and produces a signal to indicate which is greater)

  22. Applications of Comparators • Analog to digital converters (ADC) • Counters (e.g. count pulses that exceed a certain voltage level). • Cross Over Detectors

  23. OP-AMPS WITH NEGATIVE FEEDBACK The two basic amplifier circuits with negative feedback are: • The non-inverting Amplifier. • The inverting Amplifier (Note: Negative feedback is used to limit the gain)

  24. Where; VO = Output voltage Vin= Input voltage= Vf Ain= Non inverting Gain RF R1 VO VIN Figure 11 Closed-Loop Noninverting Amplifier Circuit NON-INVERTING AMPLIFIER • The input signal is applied to the non-inverting input (+VIN). The output is fed back to the inverting input through resistor RF.

  25. Problem: • Calculate the gain of a non inverting amplifier if Rin=3K and Rf=30K. If Vin=4mV, calculate the output voltage.

  26. RF RIN VIN VO Where; VO = Output voltage VIN = Input voltage AI = Inverting Gain INVERTING AMPLIFIER • The input signal is applied through a series input resistor RI to the inverting input. Also, the output is fed back through RF to the same input. The noninverting input is grounded.

  27. Examples of Negative Feedback Applications: A) Inverting Amplifiers 1.Summing Amplifier 2.Differentiator 3.Integrator B) Non Inverting Amplifiers 1. Voltage Follower

  28. R1 RF V1 R2 V2 VO R3 V3 0V Figure 14 Summing Amplifier Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal value, thenVo = -(V1 + V2+ V3)

  29. R C VO VIN Figure 16 Inverting Op-Amp as Differentiator Differentiator (the input is differentiated with respect to time)

  30. C R VIN VO Figure 15 Inverting Op-Amp as Integrator Integrator (the input is integrated with respect to time)

  31. Figure 17 Voltage Follower VO VIN Voltage Follower (Non Inverting) • It is a non inverting amplifier with gain=1 • So the output is the same as input.

  32. R1 C1 VO R2 R3 Figure 13 A stable Multi-vibrator Positive Feedback is used in oscillators • AstableMultivibrator (Relaxation Oscillator)

  33. 8 7 6 5 A741 1 3 4 2 VO V +VS N/C Figure 22Offset Null adjustment -VS VIN = 0 Offset Null Adjustment (practical)

  34. offset voltagecan be defined as the slight amount of voltage that appears at the output when the voltage differential (ΔVIN) between the input pins is 0 V. For more reading on op. Amplifiers http://holbert.faculty.asu.edu/ece201/opamp.html

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