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Module 3 OPERATIONAL AMPLIFIER Brainstorming Session…. What does an AMPLIFIER do? • What is an IC? Integrated Circuits Inside an IC OP-Amp is an amplifier IC 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. 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 Operational Amplifier • 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. OP-AMP BLOCK DIAGRAM +V Inverting Input (- VIN) Differential Amplifier Voltage Amplifier Output Amplifier Noninverting Input (+ VIN) -V Figure 1 Op Amp Block Diagram Output 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) OP-AMP CHARACTERISTICS 1. Very high input impedance 2. Very high gain 3. Very low output impedance OP-AMP is a differential, voltage amplifier with high gain. 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) The 741 Op-amp The most common op-amp is the 741 IC. Packaging Types (b) OPA547FKTWT (a) Op Amp 741 DIP SMT package 8-pins DIP package Figure : Op Amp packages (c) TO-5 metal can 8-Leads package OP-AMP pins identification 1 2 3 4 +VCC - + -VEE 8 1 7 2 6 3 5 4 a) Dot marked Package 741 +VCC - 7 6 + -VEE b) Notched Package Figure 3 Op Amp pins Identification 8 5 What are these pins? 1. Offset Null 1 8 8. N / C 2 7 7. +VCC 3. Noninverting Input +VIN 3 6 6.Output VEE 4 5 2. Inverting Input –VIN - 741 5.Offset Null Figure 4 Op Amp pins Description http://www.quia.com/pp/200743.html 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 Symbol of OP-AMP +VS -VIN -VIN - - VOUT VOUT +VIN +VIN + + -VS (a) Without power connection (b) With power connection Figure 5 Op Amp Schematic Symbols Most Op Amps require dual power supply with common ground Positive Supply (+15V) to pin7 Negative Supply (-15V) to pin4 +VS -VIN 7 VOUT +VIN + 4 Common Ground -VS Figure 6 Dual Supply Voltages connection Some Op Amps work on single supply also +VS -VIN -VIN - 7 VOUT +VIN +VIN + VOUT 7 + 4 4 -VS (a) Single Positive Voltage (b) Single Negative Voltage Figure 7 Single Supply Voltages connection Advantage of dual power supply Using dual power supply will let the op amp to output true AC voltage. +15V Output 0V Output 30 V -15V Figure 8a Op Amp powered from Dual supply +30V 30 V 0V Figure 8b Op Amp powered from Single supply What is dual power supply? Single Power Supply –15V Single Power Supply Common Figure 18 Dual Power Supply +15V How can you make a dual power supply using two 9V batteries? What is the voltage between + of first battery and – of second battery? OP-AMP CONFIGURATIONS (a) No Feedback (open loop comparator circuit) (b) Negative Feedback Figure Types of Feedback (c) Positive Feedback 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( OP AMP as a Comparator (compares 2 voltages and produces a signal to indicate which is greater) VO +VS +VS +VIN –VIN –VIN VO 0 +VIN = –VIN +VIN +VIN –VIN –VS (a) Comparator Circuit –VS (b) Comparator Output Applications of Comparators • Analog to digital converters (ADC) • Counters (e.g. count pulses that exceed a certain voltage level). • Cross Over Detectors 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) 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. R IN R F VF VO R IN V R A NI O 1 F VF R IN Where; VO = Output voltage Vin= Input voltage= Vf ANI = Noninverting Gain R1 RF VIN Figure 11 Closed-Loop Noninverting Amplifier Circuit VO Problem: • Calculate the gain of a non inverting amplifier if Rin=3K and Rf=30K. If Vin=4mV, calculate the output voltage. 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. R VO F VIN R IN R V A I O - F VF R IN Where; VO = Output voltage VIN = Input voltage AI = Inverting Gain RIN RF VIN VO Examples of Negative Feedback Applications: A) Inverting Amplifiers 1.Summing Amplifier 2.Differentiator 3.Integrator B) Non Inverting Amplifiers 1. Voltage Follower Summing Amplifier (Adder) : the inputs are added and the sum is inverted . If all resistors are of equal value, then Vo = -(V1 + V2+ V3) R1 RF V1 R2 V2 VO R3 V3 0V Figure 14 Summing Amplifier Integrator (the input is integrated with respect to time) C R VIN VO Figure 15 Inverting Op-Amp as Integrator Differentiator (the input is differentiated with respect to time) R C VIN VO Figure 16 Inverting Op-Amp as Differentiator Voltage Follower (Non Inverting) • It is a non inverting amplifier with gain=1 • So the output is the same as input. VO VIN Figure 17 Voltage Follower Positive Feedback is used in oscillators • Astable Multivibrator (Relaxation Oscillator) R1 C1 VO R2 R3 Figure 13 Astable Multivibrator Offset Null Adjustment (practical) • VO V +VS N/C 8 7 6 5 3 4 A741 1 2 -VS VIN = 0 Figure 22 Offset Null adjustment • offset voltage can 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. Practical-Summing Amplifier Results Table Vo = - (V1 + V2 )