Operational Amplifier (Op-Amp) - Study Guide
An Operational Amplifier (Op-Amp) is a high-gain voltage amplifier designed for signal processing,
mathematical operations, and analog computations. It is a key component in analog electronics used
in filters, amplifiers, and signal conditioning circuits.
1. Features of an Op-Amp
• High Gain: Very high open-loop voltage gain (typically 10⁵ to 10⁶).
• High Input Impedance: Minimizes loading effects.
• Low Output Impedance: Ensures efficient signal transfer.
• Differential Inputs: Two inputs – Inverting (-) and Non-Inverting (+).
• Wide Frequency Response: Operates over a large range of frequencies.
• Low Offset Voltage: Ideally, the output should be zero when inputs are equal.
2. Op-Amp Symbol & Pin Configuration (IC 741)
The most common Op-Amp is the 741 Op-Amp, an 8-pin IC.
2.1 Symbol
+Vcc
(-) ----| |---- Output
(+) ----| |
-Vee
2.2 Pin Configuration (IC 741)
Pin Function
1 Offset Null
2 Inverting Input (-)
3 Non-Inverting Input (+)
4 Negative Power Supply (-Vcc)
5 Offset Null
6 Output
Pin Function
7 Positive Power Supply (+Vcc)
8 Not Connected
3. Op-Amp Operating Modes
An Op-Amp operates in two main modes:
3.1 Open-Loop Mode (Comparator)
• No feedback is used.
• The output is saturated (±Vcc) based on the difference between inputs.
• Used in comparator circuits.
3.2 Closed-Loop Mode (Feedback Applied)
• Negative Feedback: Stabilizes gain, improves bandwidth, reduces distortion.
• Positive Feedback: Used in oscillators and regenerative circuits.
4. Ideal vs. Practical Op-Amp
Parameter Ideal Op-Amp Practical Op-Amp
Input Impedance ∞ 10⁶ – 10¹² Ω
Output Impedance 0 10 – 100 Ω
Open-Loop Gain (AOL) ∞ 10⁵ – 10⁶
Bandwidth ∞ Limited (~1 MHz for 741)
Offset Voltage 0V Small (~mV range)
5. Op-Amp Configurations
5.1 Inverting Amplifier
• The input signal is applied to the inverting input (-).
• Gain: Vout=−(RfRin)VinV_{out} = - \left(\frac{R_f}{R_{in}}\right) V_{in}
• Phase Shift: 180°.
5.2 Non-Inverting Amplifier
• The input is applied to the non-inverting input (+).
• Gain: Vout=(1+RfRin)VinV_{out} = \left(1 + \frac{R_f}{R_{in}}\right) V_{in}
• Phase Shift: 0°.
5.3 Voltage Follower (Buffer)
• Used to provide high input impedance and low output impedance.
• Gain: 1 (No amplification).
• Used in impedance matching.
5.4 Summing Amplifier
• Adds multiple input signals.
• Output: Vout=−(V1+V2+V3)V_{out} = - (V_{1} + V_{2} + V_{3})
5.5 Differential Amplifier
• Amplifies the difference between two inputs.
• Output: Vout=Ad(V1−V2)V_{out} = A_d (V_1 - V_2)
5.6 Integrator
• Performs mathematical integration (∫).
• Output: Vout=−1RC∫VindtV_{out} = -\frac{1}{RC} \int V_{in} dt
• Used in signal processing and waveform generation.
5.7 Differentiator
• Performs mathematical differentiation (d/dt).
• Output: Vout=−RCdVindtV_{out} = -RC \frac{dV_{in}}{dt}
• Used in edge detection circuits.
6. Op-Amp Applications
• Signal Amplifiers (Audio, Instrumentation)
• Active Filters (Low-pass, High-pass, Band-pass)
• Oscillators (Sine, Square, Triangle Wave Generators)
• Analog Computation (Addition, Integration, Differentiation)
• Voltage Regulators
• Comparators (Zero-crossing detection, Schmitt
