Operational Amplifiers

An operational amplifier (op-amp) is a high-gain electronic voltage amplifier with a differential input and a single-ended output.

Originally used for mathematical operations (e.g., addition, subtraction, integration, differentiation).

Modern op-amps are linear integrated circuits (ICs):

• Operate with low DC supply voltages.

• Reliable and cost-effective.

Applications: signal amplification, filtering, analog computing, and more.

Two inputs: Inverting (\(-\)) and Noninverting (\(+\)) and One output.

Typically powered by dual DC supplies (\(+V_{\text{CC}}\), \(-V_{\text{CC}}\)) or single supply.

Common IC packages: dual in-line (DIP), surface-mount technology (SMT).

1947: Concept of op-amps proposed as analog building blocks.

Early op-amps used vacuum tubes (high voltages).

1964: First IC op-amp developed by Fairchild Semiconductor designated as 702.

Later Developments: Fairchild 709 and 741 (industry standard).

Modern op-amps benefit from IC technology: compact, efficient, and versatile.

Infinite voltage gain: \(A_{\text{ol}}\to \infty\).

Infinite bandwidth: Amplifies all frequencies equally.

Infinite input impedance: \(Z_{\text{in}}\to \infty\) (no input current).

Zero output impedance: \(Z_{\text{out}}= 0\) (ideal voltage source).

Zero noise: No unwanted signals.

Very high voltage gain: \(A_{\text{ol}}\approx 10^5 - 10^6\).

Very high input impedance: \(Z_{\text{in}}\approx 10^6 - 10^{12} \Omega\).

Very low output impedance: \(Z_{\text{out}}\approx 50 - 100 \Omega\).

Limited bandwidth: Gain decreases at high frequencies.

Non-zero noise: Internal noise affects signal quality.

Voltage and current limitations:

• Output voltage limited to \(\pm V_{\text{CC}}\) (slightly less).

• Current limited by power dissipation and component ratings.

Composed of three main stages:

1. Differential Amplifier: Input stage, amplifies difference between inputs.

2. Voltage Amplifier: Provides additional gain (Class A).

3. Push-Pull Amplifier: Output stage (Class B) for efficient power delivery.

Differential Mode:

• Single-Ended: One input grounded, signal on the other.

• Double-Ended: Two out-of-phase signals applied.

• Output amplifies the difference between inputs.