AD623 Instrumentation Amplifier & Its Working

• The AD623 is an Instrumentation Amplifier with Rail to Rail feature. It also operates at a very low current of 550nA making it suitable for battery-operated applications.

Instrumentation amplifier:

• An instrumentation amplifier (sometimes shorthanded as in-amp or In Amp) is a type of differential amplifier that has been outfitted with input buffer amplifiers.
• These buffer amplifiers eliminate the need for input impedance matching and thus make the amplifier particularly suitable for use in measurement and test equipment.

Rail to rail Op-Amp:

• The output stage transistors prevent the amplifier from reaching the maximum positive voltage or minimum negative voltage.
• Therefore, the output pin of a normal op-amp will not be able to provide a voltage that is equal to the supply voltage.
• But the Rail to Rail Op-Amp overcomes this problem and hence the output pin can reach either positive rail voltage or negative rail voltage.
• Terms rail-to-rail input/output (RRIO) and rail-to-rail output (RRO).
• If an op amp can drive RRO, it means you have a good dynamic range in which to work on the signal. A related term, headroom, is a measure of how close the signal comes to the rails.

WORK of AD623

• The AD623 only requires a resistor to sets its gain value and hence can be easily set up. A very basic commonly used circuit for AD623 is shown below.
• The IC is powered using pin 7 and pin 4, here I have used a singly supply of +5V hence pin 4 is grounded.
• If a dual supply voltage is used pin 4 will be provided with negative voltage.
• The non-inverting pin (pin 2) and the inverting pin (pin 3) are connected to the signal which has to be amplified or compared based on the application of the Op-Amp.
• The Reference pin (pin 5) is normally grounded along with pin 4, the reference pin is used to direct the output towards a voltage when the difference voltage between the inverting and the non-inverting pin is 0V.

PIN Description

Applications of AD623

• Low power medical instrumentation
• Transducer interfaces
• Thermocouple amplifiers
• Industrial process controls
• Difference amplifiers
• Low power data acquisition