Op Amps-Operational Amplifiers

Introduction to Operational Amplifiers

Op-amp circuit

An operational amplifier, abbreviated as op-amp, is basically a multi-stage, very high gain (typically 2,00,000), direct-coupled, negative feedback amplifier that uses voltage-shunt feedback to provide a stabilized voltage gain. An op-amp has high input impedance (ex­ceeding 100 kilo Ohms) and low output impedance (less than 100 Ohms) and has capability of ampli­fying signals having frequency ranging from zero Hz to 1 MHz, that is, op-amp can be used to amplify dc as well as ac input signals. Although discrete op-amps are built, designers of industrial electronic circuit now use integrated circuit operational amplifiers (IC op-amps) almost exclusively. They are made with different internal configurations in linear ICs. An op-amp is so named as it was originally designed to perform mathematical operations such as summation, subtraction, multiplication, differentiation and integration etc. Now-a-days, the op-amps are put to a variety of other uses such as sign changing, scale changing, phase shifting, voltage regulation, analog computer operations, in instrumentation and control systems, oscillator circuits, pulse generators, square-wave generators, triangular-wave generators, comparators, analog to digital and digital to analog converters (ADC and DAC); voltage-to-current converters, current-to-voltage converters, sample-and-hold cir­cuits etc.

The op-amp manufactured with integrated transistors, diodes, resistors and capacitors, is an extremely versatile device that is found doing countless tasks, as enumerated above and many more. The op-amp is a complete amplifier having the advantages of an IC such as low cost, small size, high reliability, temperature stability and low value of offset voltage and current. Furthermore, it is designed in such a way that external components like resistors, capacitors etc. can be connected to its terminals and external characteristics can be changed. Various amplifier characteristics can be tailored to fit a particular application merely by changing a few components, without redesigning the entire amplifier. This is because the voltage gain, input impedance, output impedance, and frequency bandwidth depend almost solely on stable external resistors and capacitors. The voltage gains of IC op-amps are extremely large, typically 2,0,000. Because of this large voltage gain, externally connected resistors must be employed to provide negative feedback for most of the applications