OPERATIONAL AMPLIFIER

An operational amplifier or popularly known as Op-Amp, is a solid state IC with transistors that uses external feedback to control its functions. It has a very high gain.

How it works

It is an integrated circuit with individual transistors and has a non-inverting input (+), an inverting input (-) and one output. The output voltage is the difference between the + and - inputs multiplied by the open-loop gain.

The basic design has three stages:

Differential amplifier: at the input stage, it lowers noise amplification
Voltage amplifier: gives high voltage gain
Output amplifier: gives high current driving capability

Selection of operational amplifier

The device should have low distortion, low noise and wide bandwidth. The device can be damaged by ESD. Nodal analysis is used to analyze op amp circuits. Offset voltage is sometimes laser trimmed.

Input voltage range: range of the input voltage (e.g. +/- 5V to +/- 25V)
Output voltage: voltage at the output (e.g. +/-12V)
Bandwidth gain: refers to the total gain in the bandwidth (20 MHz)
Open loop gain: amplification from input to output without any feedback applied (e.g. 80 to 100 dB)
Load: load carried (Ohms)
Operating temp: usually between –25 deg C to +85 deg C
Power dissipation: internal power dissipation is higher at higher supply voltage

Types of op-amp

They are specified based on their mounting, input resistance, output resistance, and voltage gain. The main types are: inverting amplifier, non-inverting amplifier, voltage follower, difference amplifier, summing amplifier, integrator, differentiator, comparator, instrumentation amplifier, Schmitt trigger, inductance gyrator.

Applications

They are used in professional audio equipment, SWOP amplifiers, audio and video pre-amplifiers and buffers, PCM DAC I/V converters, spectral analysis equipment, transducer amplifiers, and data acquisition voltage comparators. Other uses are in differential amplifiers, differentiators and integrators, filters, precision rectifiers, voltage and current regulators, analogue calculators, analogue-to-digital converters, digital-to-analog converters, and ultrasonic distance measurement.