Introduction to Op-amp (Operational Amplifier)
In this “Introduction to Op-amp” topics related to general term Op-amp is explained only. No specific topic of any Op-amp (for example IC 741) is explained in this article.
Definition: One electronic device which is a special type of amplifier and can be used for variety of operations such as addition, subtraction, differentiation and integration is called OPerational AMPlifier (Op-amp). It is one amplifier and can perform various operations, therefore it is named as operational amplifier.
The term op-amp was coined in 1947 by John R. Ragazzini to specify special type of amplifier that can perform mathematical operations. Initially, these op-amps were mainly made up of vacuum tubes.
These op-amps of vacuum tubes were large, bulkier, and high power consuming devices. Hence after a decade of the vacuum tube, op-amps began to be replaced by miniatured solid-state op-amps.
Karl D. Swartzel Jr. invented the first op-amp in 1967 and he originally considered them to do mathematical operations in analog computers.
Importance of Op-amp
- We can construct amplifiers, waveform generators and timers using Op-amp.
- Various circuits like adder, Subtractor, differentiator and integrator etc. can be built using op-amp.
- The op-amp has become an integral part of almost every electronic circuit which uses linear integrated circuits (ICs).
- The op-amp is basically an excellent high gain d.c. amplifier.
- A variety of useful circuit can be built without the necessity of knowing about the complex internal circuitry.
- Op-amps are inexpensive, take up less space and consume less power.
Due to these various usage the significance of op-amp is very much. Thus it became an integral part of almost every Electronic circuit which uses an analog IC.
Block Diagram of Op-amp
The block diagram of the Operational Amplifier is shown in the following figure.
The op-amp consist of mainly four stages. Each stage is an electronic circuit and perform some operations.
- Input stage: The Input stage is a dual-input and balanced output differential amplifier . This stage provides most of the voltage gain of the amplifier and also establishes the input resistance of the op-amp.
- Intermediate Stage: Intermediate stage increases the overall gain of the op-amp. It is dual input unbalanced output differential amplifier.
- Level shifting stage: It is an emitter follower with constant current source. This circuit is used after intermediate stage to shift the d.c. level at the output of the intermediate stage downwards to zero volt with respect to ground.
- Output Stage: The last stage is a complementary symmetry push-pull amplifier . It increases voltage and current handling capability of op-amp. It also provides a low output resistance.
As every block is nothing but a circuit. The circuit diagram of each block alog with its operation is explaned in video tutorial of our YouTube channel. Click here to watch it.
The circuit symbol of the op-amp is shown below.
The symbol looks like an arrowhead which indicates the signal flow from input to output. All the op-amps have at least following five terminals.
- Positive supply voltage terminal +VCC or +V or +VS.
- Negative supply voltage terminal –VCC or -V or – VS.
- The output terminal.
- Inverting input terminal, marked as negative.
- Non–inverting input terminal, marked as positive
Equivalent Circuit of Op-amp
The figure shows an equivalent circuit of an op-amp.
Here, AVid is an equivalent Thevenin’s Voltage source and Ro are the Thevenin’s equivalent resistance.