OPERATIONAL AMPLIFIER

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OPERATIONAL AMPLIFIER (OP – AMP ) 1 weyes57

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By V.SUBRAMANIAN, P.G.TEACHER (PHYSICS), GOVERNMENT HIGHER SECONDARY SCHOOL, MANALI, CHENNAI – 600 068, TAMIL NADU STATE , INDIA. 2 weyes57

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3 weyes57 CONTENT Introduction Components inside an op.amp. Characteristics of an op.amp. Circuit symbol and pin configuration Top view Pin-out configuration Inverting amplifier Non inverting amplifier Summing amplifier Difference amplifier

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OPERATIONAL AMPLIFIER ( OP AMP ) OP - AMP is a solid state device capable of sensing and amplifying dc and ac input signals. OP – AMP is an amplifier with two inputs (Differential inputs) and a single output. 4 weyes57

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OPERATIONAL AMPLIFIER ( OP AMP ) OP – AMP consists of 20 transistors 11 resistors and 1 capacitor. OP - AMP requires a positive and negative power supply( Dual power supply ). This allows the output voltage to swing positive and negative with respect to ground. 5 weyes57

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OP – AMP consists of 20 transistors 11 resistors and 1 capacitor. 6 weyes57

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CHARACTERISTICS OF AN OP - AMP VERY HIGH INPUT RESISTANCE OR EVEN INFINITY WHICH PRODUCES NEGLIGIBLE CURRENT AT THE INPUT. VERY HIGH CURRENT GAIN. VERY LOW OUTPUT IMPEDANCE OR EVEN ZERO,SO AS NOT TO AFFECT THE OUTPUT OF THE AMPLIFIER BY LOADING. 7 weyes57

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An OP – AMP is so named, because it was originally designed to perform mathematical operations such as addition, subtraction, multiplication, division, integration, differentiation etc in analog computer. Nowadays OP - AMPs are used in analog computer operations and in timing circuits. 8 weyes57

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The Op – Amp is represented by a triangular symbol . It has two input and one output terminals. CIRCUIT SYMBOL AND PIN-OUT CONFIGURATION 9 weyes57

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The terminal with negative sign (-) is called inverting input. The terminal with positive sign (+) is called non inverting input. The input terminals are at the base and the output is at the apex of the triangular symbol. 10 weyes57

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The widely used and most popular type is Op – Amp IC 741. The top pin on the left side of the notch is pin 1. The pin number 2 is inverting input and pin number 3 is non-inverting input terminal. 11 weyes57

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The pin number 6 is the output terminal. A dc voltage or ac signal connected to pin 2 will be 180o out of phase at the output. A dc voltage or ac signal connected to pin 3 will be in phase at the output. Pin 4(-) and 7(+) are the power supply terminals. 12 weyes57

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The pin 1 and 5 are Null adjustment pins. Null adjustment pins are used to null the output voltage , when equal voltages are input terminals for perfect balance. Pin number 8 indicates No connection. 13 weyes57

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TOP VIEW OF 8 PIN DIP Notch 741 14 weyes57

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OP – AMP Pin- out configuration 15 weyes57

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We are using the two ideal op amp properties discussed above to analyze this circuit.   Since the amplifier has infinite gain, it will develop its output voltage, Vout, with zero input voltage. 1. INVERTING AMPLIFIER 16 weyes57

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Since the differential input is zero, the full input voltage must appear across Ri, making the current in Ri, Iin = Vin / Ri . since there is no current flow into either input terminal because the input impedance is infinite, the current Iin must also flow in Rf. 1. INVERTING AMPLIFIER 17 weyes57

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Then, -Vout / R2  = Vin / Ri    Voltage Gain (Av) is equal to = Vout / Vin = - Rf / Ri Vout = - Rf / Ri (Vin ) The output voltage is out of phase with the input voltage. 1. INVERTING AMPLIFIER 18 weyes57

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2.THE NON INVERTING AMPLIFIER The input signal is applied to the non inverting input terminal. A resistor R1, is connected from the inverting input to the ground. The feedback resistor R2 is connected between the output and the inverting input. 19 weyes57

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2.THE NON INVERTING AMPLIFIER The resistances R1 and R2 form a resistive net work to produce the feedback voltage VA needed at the inverting input. The feedback voltage VA is developed across R2 . 20 weyes57

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2.THE NON INVERTING AMPLIFIER Since the potential at the inverting input and that at the non inverting input are same . VA = VIN. A v = VOUT / VIN VA = ( R1 / R1 + R2 ) x VOUT 21 weyes57

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2.THE NON INVERTING AMPLIFIER (R1 + R2 / R1) = VOUT / VA 1 + ( R2 / R1) = VOUT / VIN A v = 1 + ( R2 / R1). The output and input voltages are in phase. 22 weyes57

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3.The Summing Amplifier The summing amplifier provides an output equal to the sum of the input voltages. Here we have an inverting amplifier, used to sum two input voltages. 23 weyes57

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The Summing Amplifier The input voltages V1 and V2 are connected to the inverting input through the resistors R1, R2 and RF is the feedback resistance. 24 weyes57

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The Summing Amplifier At the junction I1 + i2 = if V1/R1 + V2/R2 = Vout / RF V1 RF /R1 + V2 RF /R2 = Vout V1 = V2 = RF = R then, Vout = - (V1 + V2 ) I1 I2 If 25 weyes57

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Difference Amplifier In this amplifier the output is obtained by superposition principle. First find the output due to input V2 alone, assuming that V1 is shorted to ground. 26 weyes57

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Difference Amplifier V+ = (R4 / R3+R4)V2 V02 = ( R1+R2 / R1 )V+ ( Non Inverting Amplifier) V02 = ( R1+R2 / R1 ) (R4 /R3+R4)V2 V+ 27 weyes57

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Now assuming V2 is shorted to ground, the output due to V1 alone is given by, V 01 = - (R2 / R1 ) V1 (Inverting Amplifier) V0 = V 02 + V 01 Difference Amplifier 28 weyes57

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V02 = ( R1+R2 / R1 ) ( R4 /R3+R4 )V2 – ( R2 / R1 ) V1 If R1 =R2 = R3 = R4 then, V0 = V2 – V1 Difference Amplifier If all the external resistances are equal, the voltage difference amplifier functions as a voltage subtractor. 29 weyes57

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30 weyes57 THANK YOU THE END. Kindly visit www.freewebs.com/weyes57