Operational Amplifier (Op-Amp)
The popular name of operational amplifier is op-amp. The operational amplifier is an active device used to design circuits that perform useful operations. The main operation of operational amplifier is
- to generating sine waves or square waves
- differentiating and
- removing noise; and
- transforming alternating current into direct current and vice-versa.
Description of Op-Amp
- It can also change the shape of a waveform, produce a change in the output when an input signal reaches a certain level.
- It provides constant voltage or current and performs various other important circuit operations.
- Op-amp circuits are very important as we develop a valuable perception of how electronic circuits work in general.
- An op-amp is a very high-gain differential amplifier with high input impedance and low output impedance.
- The above figure shows a basic op-amp with two inputs and one output. The negative terminal is known as the inverting input terminal (Input 1), and the positive terminal is known as the non-inverting input terminal (Input 2).
- Each input results in an output, which further depends upon the input that is being applied to positive (+) or negative (−) input terminals.
- The op-amp is known as the differential amplifier because it amplifies the voltage difference of the inverting and non-inverting terminals.
Properties of The Ideal Operational Amplifier
An ideal op-amp should have the following properties:
- Gain must be infinite.
- Output voltage must be zero when input voltages are the same or when both are zero.
- The input resistance must be infinite.
- The output resistance must be zero.
- The common mode rejection ratio (CMMR) must be infinite.
- Infinite bandwidth, i.e., it must allow all frequencies to pass.
- Op-amp characteristics should not drift with temperature.
All these parameters for an ideal op-amp are different from those of a practical op-amp, as illustrated by the comparison given in table
|Op-amp Parameters||Ideal Op-amp Parameters||Practical Op-amp Parameters|
|Gain||Infinite||103 to 106 order|
|Output voltage||Zero (0 volt)||Few volts (in μV or nV), due to offset|
|Input resistance||Infinite||103 Ω to 106 Ω order|
|Output resistance||Zero (0 Ω)||Few ohm (Ω) order|
|CMRR||Infinite||100 dB order|
|Bandwidth||Infinite||Mega Hz order|
|Slew rate||Infinite||0.5 V/μs order|
Table Comparison between the parameters of an ideal op-amp and a practical op-amp
SPECIFICATIONS OF IC 741C
The op-amp popularly used in the laboratory is IC 741C. It is an eight (8) pin DIP (dual input package) IC, as shown in the figure.
Description of Op-Amp 741 IC Pins
|Pins 1 and 5:||These two pins are used for the offset null process.|
|Pin 2:||Inverting input terminal, i.e., when a sinusoidal signal is applied to the input pin 2, the inverted output is obtained at the output terminal 6.|
|Pin 3:||Non-inverting input terminal, i.e., when a sinusoidal signal is applied to the input pin 3, the waveform of the same phase output is obtained.|
|Pin 4:||− Vcc, i.e., the negative terminal of the supply voltage is connected to this pin.|
|Pin 6:||Output terminal.|
|Pin 7:||+ Vcc, i.e., positive terminal of the supply voltage is connected to this pin.|
|Pin 8:||No electrical connection is there in this pin; this pin is just for balance and the symmetric dual-input package look.|
APPLICATIONS OF THE OPERATIONAL AMPLIFIER
The op-amp is used either in inverting mode or non-inverting mode. In many practical applications, the op-amp is used as an adder, subtractor, intergrator, integrator, differentiator, voltage follower, phase changer, etc.