An Operational Amplifier (Op-Amp) is a direct-coupled, high-gain amplifier capable of performing a wide range of linear, non-linear, and mathematical operations on both AC and DC signals.

2.1 Construction

An Op-Amp is constructed from multiple stages, including one or more differential amplifiers, a level translator, and an output stage. The differential amplifier at the input stage provides two input terminals:

• Inverting Terminal: The output signal is 180° out of phase with the input signal applied to this terminal.
• Non-Inverting Terminal: The output signal is in phase with the input signal applied to this terminal.

2.2 Key Performance Characteristics

• Open Loop Voltage Gain (): The differential gain of the op-amp without any feedback path. It is mathematically expressed as: A_{v}= \frac{v_0}{v_1-v_2}.
• Output Offset Voltage: The voltage present at the output when the differential input voltage is zero.
• Common Mode Rejection Ratio (CMRR): The ratio of the closed-loop differential gain (A_d) to the common mode gain (A_c). A high CMRR is desirable. It is expressed as: CMRR=\frac{A_{d}}{A_{c}}.
• Slew Rate (SR): The maximum rate of change of the output voltage in response to a step input. It is measured in V/μSec or V/mSec and defined as: SR=Maximum\:of\:\frac{\text{d}V_{0}}{\text{d}t}.

2.3 Ideal vs. Practical Op-Amps

There is a significant difference between the theoretical characteristics of an ideal Op-Amp and the performance of a practical Op-Amp. The IC 741 is cited as the most popular practical op-amp.