Need of Instrumentation Amplifier:

As we know Instrumentation Amplifier are used to amplify the low level differential signals very precisely, in presence of the large common mode noise and interference signals. Hence a good Need of Instrumentation Amplifier has to meet the following specifications :

Finite, accurate and stable gain : As very low level signals are required to be amplified by the instrumentation amplifiers, high and finite gain is the basic requirement. It is usually in the range of 1 to 100. The gain has to be accurate and closed loop gain must be stable in nature.

Easier gain adjustment : Not only finite and stable gain is required but a variable gain over the prescribed range is also required. The gain adjustment must be easier and precise. Generally such gain adjustment is done continuously using a potentiometer or is done digitally with the help of switches, which are JFET or MOSFET switches.

High input impedance : To avoid the loading of input sources, input impedance of the instrumentation amplifiers must be very high (ideally infinite). The differential mode input impedance Zid is the equivalent impedance between the two input The common mode input impedance Zic is the equivalent impedance between each input terminal and ground.

Low output impedance : Extremely low output impedance (ideally zero) to avoid the loading on the immediate stage.

High CMRR : The output of transducer, when transmitted with long transmission lines has presence of large common mode noise voltages. The instrumentation amplifier must amplify only the differential input, completely rejecting the common mode input component. Thus it must have ideally infinite CMRR.

Low power consumption : The power consumption of an Instrumentation Amplifier should be as low as possible.

Low thermal and Time drifts : The parameters of the instrumentation amplifier, should not drift with temperature or time.

High slew rate : The slew rate of the instrumentation amplifier must be as high as possible to provide maximum undistorted output voltage swing.

The amplifier must have differential input so that it can be amplified.