Operational Amplifier(OPAMP) Operational amplifier is a direct-coupled amplifier used to perform wide variety of linear and some nonlinear operations which is usable in the frequency range from 0 to few MHz. (TOAL No of Slides is 14) Some features of OPAMP OPAMP was designed to perform mathematical operations such as summation, subtraction, multiplication, differentiation, integration etc. in analog computer. OPAMP can also be used for the purpose of solution of simultaneous linear algebraic equation as well as differential equation. Now a days OPAMPs are available almost all in IC forms having comparatively low price. Many useful circuits can be designed using OPAMP and so this has become very popular in electronic industry. Pin Diagram & Circuit symbol of OPAMP Characteristics of ideal OPAMP Open loop voltage gain is infinite Input impedance is infinite Output impedance is zero Bandwidth is infinite Perfect balance i.e, ouput is zero when two input voltage are equal. Characteristics do not drift with temperature Common mode rejection ratio is infinite Slew rate is infinite Deviations of practical amplifier from ideal one In practical OPAMP Open Loop Voltage gain is not infinite Input impedance is not infinite CMRR is not infinite Output is not zero even if two input voltages are identical. The voltage which should be applied between the input terminals to balance the amplifier is called input offset voltage. where as the input offset current is the difference between the two bias currents entering into the input terminals of balanced amplifier and input bias current is the average of two separate currents entering the input terminals of a balanced amplifier. Applications of OPAMP OPAMP can be used both in inverting mode and non inverting mode. However OPAMP can be used for designing i) Scale changer ii) Phase Shifter iii) Unity gain follower iv) Adder v) Subtractor vi) Differential amplifier vii) Integrator viii) Differentiator Inverting Amplifier • Op-amp are almost always used with a negative feedback: Part of the output signal is returned to the input with negative sign Feedback reduces the gain of op-amp Since op-amp has large gain even small input produces large output, thus for the limited output voltage (lest than VCC) the input voltage vx must be very small. Practically we set vx to zero when analyzing the op-amp circuits. with vx =0 i1 = vin /R1 i2 = i1 and vo = -i2 R2 = -vin R2 /R1 so Av=vo /vin =-R2 /R1 ……………(1) Scale changer and Phase Shifter • From (1) , R2 v0 vs kvs R1 i.e the circuit multiplies the input by –k and so such circuit can be treated as scale changer. If , R1 and R2 is replaced by impedances z1 and z2 and they are chosen in such a way that they have equal magnitude but different phase then v0 Iz2 Ie j2 j ( 2 1 ) e vs Iz2 Ie j1 Where 1and 2 are respectively the phase angles of z1 and z2.Thus the OPAMP can shift the phase of input voltage by the angle 2 1 Non Inverting Amplifier Here signal is applied in non-inverting terminal. Since gain A There is a virtual short at the input terminals and so, v0 v2 v2 0 R2 R1 or , v0 v R 0 1 2 vs v2 R1 .........(1) Unity gain follower From eq (2)it is found that the closed loop gain becomes unity if we choose R1 and/or . R2 0 . The amplifier then acts a voltage follower i.e, a non-inverting amplifier with unity gain. OPAMP as Adder Thus the output is proportional to the algebraic sum of the inputs. OPAMP used for difference of two signals OPAMP as Integrator OPAMP as differentiator

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising