An amplifier is a circuit which can produce an output voltage, which is the product of input voltage with a value called voltage gain. An op-amp (operational amplifier) is a kind of amplifier circuit which can perform an operation (addition, subtraction etc.) on the input voltages, apart from simply amplifying the input.
An op-amp (operational amplifier) is an electronic circuit made of several active devices (transistors) and passive devices (resistor, capacitors) etc. which is capable of realizing following the common features:
-extremely high voltage gain
-can amplify input current at the output
-can invert the input voltage at the output
-can produce a sum of input voltages at the output
-can produce a sum of input currents at the output
History of op-amp
For every significant invention in history, there must be a time before such an invention where there was a necessity for such a thing. Before op-amps also, there were amplifiers. But they were designed for constant gain only. They were made using vacuum tubes and other components. Moreover the maximum gain of a particular amplifier was limited by the specifications of the vacuum tube.
This was really a problem, especially in early day’s telephone network. The telephone lines used to have thousands of meters long and amplifiers need to be implemented for signal boosting. Those day’s amplifiers had less gain and were very sensitive to temperature and humidity. At each points of the network, amplifiers with different gain were separately designed and implemented.
The telephone engineers in Bell labs were trying to figure out a solution for this. Finally an engineer named Harry Black came up with an idea. Design a general amplifier circuit with gain many times more than any of the normal requirement and then reduce the gain according to required levels using a negative feedback system with that amplifier. Bell labs successfully designed such a circuit using vacuum tubes before 1940s. This ingenious idea triggered the era of op-amps.
The term op-amp first appeared in a patent produced by Karl D. Swartzel of Bell Labs in 1941. This amplifier was capable of doing a summing operation on the input voltages.
First op-amp circuit