Instrumentation Amplifier

In an electrocardiography machine, electrodes detect small electrical changes on the skin resulting from heart muscle depolarization during each heartbeat.

These microvolt-range signals can be overwhelmed by noise or interference.

To rectify this, the ECG machine uses an instrumentation amplifier to amplify the ECG waveform while minimizing common-mode noise signals.

The instrumentation amplifier is a type of difference amplifier. It includes six resistors, three terminals, and an external resistor connected between the gain set terminals.

It amplifies small differences between input signals while rejecting signals common to both inputs.

The output voltage is the product of the voltage gain and the input voltage difference., The gain can be easily adjusted by varying only the external resistor.

Instrumentation amplifiers have high input impedance, low output impedance, high gain stability, and a high common mode rejection ratio.

The high input impedance prevents signal distortion by avoiding signal load, and high CMRR helps reject noises picked by the electrode leads, like electrical interference from other equipment.

Instrumentation amplifiers are used in biomedical instrumentation and telecommunication.