Differential voltage-gain device that amplifies the difference between the voltages existing at its two input terminal. An instrumentation (or instrumentational) amplifier is a type of differential amplifier that has been outfitted with input buffer amplifiers, which eliminate the need for input impedance matching. ier

Main: to amplify small signals that may be riding on large common-mode voltages. Other: particularly suitable for use in measurement and test equipment, used where great accuracy and stability of the circuit both short and long-term are required.

High input impedance High common-mode rejection Low output offset Low output impedance Additional characteristic very low DC offset low drift low noise

 An integrated circuit that internally has three operational amplifiers and several resistors.  The voltage gain is usually set with an external resistor FIGURE 1 The basic instrumentation amplifier using three op-amps.

Figure above show that Op-amps A1 and A2 are noninverting configurations that provide high input impedance and voltage gain. While, Op-amp A3 is used as unity-gain differential amplifier with high precision resistor that are all equal in value (R3=R4=R5=R6)

The gain-setting resistor, is connected externally as shown in figure 2. Op-amp A1 receives the differential input signal on its noninverting (+) input and amplifies this signal with a voltage gain of

Op-amp A1 also has as an input signal to it inverting (-) input through Op-amp A2 and the path formed by and. The input signal is amplified by Op-amp A1 with the voltage gain of The overall closed-loop gain

 where = = the equation above show the gain can be set by the value of the external resistor when and have a known fixed value  So, external gain setting resistor, is

Use this equation 100Ω