## Operational Amplifier

An * operational amplifier* is a circuit that can perform such
mathematical operations as addition, subtraction, integration and
differentiation. Operational Amplifier, also known as OP-Amp, is
basically a voltage amplifying device designed to be used with components like
capacitors and resistors, between its input and output terminals.

OP-Amp is a linear devices that are ideal for DC amplification and is used
often in signal conditioning, filtering or other mathematical operations. The
block diagram of an operational amplifier is shown below. Note that OP- Amp is
a multistage amplifier. The three stages are : differential amplifier input
stage followed by a high-gain CE (Common-Emitter) amplifier and finally the
output stage. **The key electronic circuit in an OP-Amp is the ****differential
amplifier**.

Block diagram of OP-Amp |

### An operational amplifier have the following characteristics

- The input stage of an OP-Amp is a differential amplifier (DA) and the output stage is typically a class B push-pull emitter follower.
- An operational amplifier has very high input impedance (ideally infinite) and very low output impedance (ideally zero).
- An operational amplifier has very high open-loop voltage gain ; typically more than 200000.
- The operational amplifier are almost always operated with negative feedback.

The effect of high input impedance is that the amplifier will draw a very small current (ideally zero) from the signal source. The effect of very low output impedance is that the amplifier will provide a constant output voltage independent of current drawn from the source.

### Schematic Symbol of Operational Amplifier

The basic operational amplifier has five terminal : two terminals for
supply voltages +V and -V ; two input terminals (* inverting input and
non-inverting input*) and one output terminal.

Schematic Symbol of OP-Amp |

## Slew Rate

The * slew rate* of an OP-AMP is a measure of how fast the
output voltage can change and is measured in volts per microsecond (V/µS).
Since frequency is a function of time, the slew rate can be used to determine
the maximum operating frequency of the OP Amp as follows :

f_{max} = slew rate / {2πV_{pk}}

Here V_{pk }is the peak output voltage.