Q.What is an Operational Amplifier? Write the properties of an Ideal Operational Amplifier and also draw its equivalent circuit.

An operational amplifier is a direct-coupled, high-gain amplifier with high input impedance and low output impedance, used to perform mathematical operations such as addition, subtraction, integration and differentiation.

[!ANSWER]

An op-amp is a direct-coupled, high-gain, high-input-impedance, low-output-impedance, high-bandwidth amplifier whose gain is controlled by feedback. An ideal op-amp has infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth, infinite CMRR, infinite slew rate and zero input offset voltage. Its ideal equivalent circuit is a single dependent source $A_d V_d$ driving the output.

[!TLDR]

An op-amp is a direct-coupled, high-gain amplifier with very high input impedance and very low output impedance; an ideal op-amp has infinite gain, infinite input impedance, zero output impedance, infinite bandwidth and CMRR, and its equivalent circuit is just a dependent voltage source $A_d V_d$ at the output.

Operational amplifier: The operational amplifier (op-amp) is a direct-coupled, high-gain amplifier with high input impedance, low output impedance and high bandwidth, whose gain can be controlled by feedback. It is used to perform mathematical operations such as addition, subtraction, inversion, differentiation and integration — hence the name operational amplifier.

Properties of an ideal op-amp:

Because the input impedance is infinite, no current is drawn from the source ($i_b = 0$) and the previous stage is not loaded. Because the output impedance is zero, the op-amp can drive any load without loss. Because the gain is infinite, the differential input voltage needed for a finite output is essentially zero ($V_d \approx 0$) — this is the basis of the virtual-ground concept.

Ideal equivalent circuit: In the ideal AC equivalent circuit the differential input voltage $V_d$ appears across the two input terminals, and the output is a single dependent voltage source $A_d V_d$ connected directly to the output terminal. Since the ideal input resistance is infinite, no input resistor is shown across the inputs; since the ideal output resistance is zero, no series output resistor is shown. (The practical equivalent adds a finite $R_i$ across the inputs and a series $R_O$ at the output.)

This definition and ideal model form a frequently asked 5-mark item in the II PUC Electronics question bank.

[!ANSWER]

An op-amp is a direct-coupled, high-gain amplifier with high input impedance and low output impedance, used to perform mathematical operations. An ideal op-amp has infinite open-loop gain, infinite input impedance, zero output impedance, infinite bandwidth, infinite CMRR, infinite slew rate and zero input offset voltage; its ideal equivalent circuit is simply a dependent voltage source $A_d V_d$ driving the output, with $V_d$ across the input terminals.