JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech III Year LINEAR AND DIGITAL IC APPLICATIONS Previous Question Paper (November/December - 2020 - R16)

An instrumentation amplifier is a high-precision differential voltage amplifier characterized by high input impedance, high common-mode rejection ratio (CMRR), and low output impedance. It is primarily used to amplify small signals in the presence of large common-mode noise.

• Circuit Configuration: The circuit consists of three operational amplifiers. The first two op-amps (A1 and A2) act as non-inverting buffers/amplifiers providing high input impedance, while the third op-amp (A3) acts as a differential amplifier.
• Circuit Diagram Description: Two input op-amps have their non-inverting terminals connected to input voltages V1 and V2. A gain-setting resistor R_g is connected between the inverting terminals of A1 and A2. The outputs of A1 and A2 are fed into the differential amplifier A3, which uses four matched resistors (R) to set the gain of the final stage to unity.
• Operation: The output voltage V_out is given by the expression:

• The gain is adjusted by varying the external resistor R_g. Because the differential gain is determined by R_g and the common-mode gain is ideally zero, the circuit provides excellent signal extraction from noisy environments.

The IC 741 is a general-purpose operational amplifier widely used in industrial and educational applications. Its key features include:

• High Open-Loop Gain: Typically around 200,000, allowing for precise control in feedback configurations.
• Internal Frequency Compensation: It includes an internal 30pF capacitor that ensures stability by preventing oscillations at high frequencies.
• Short-Circuit Protection: The output stage is designed to limit current, protecting the device from damage if the output is accidentally shorted to ground or supply rails.
• Offset Null Capability: It provides pins to nullify the input offset voltage, ensuring zero output for zero input.
• High Input Impedance: Typically 2 MΩ, which minimizes loading effects on the signal source.
• Low Power Consumption: Operates efficiently over a wide range of supply voltages (typically ±5V to ±18V).