Question

Slew rate of an ideal op-amp is

• A. \( \text{Infinite} \)
• B. \( \text{Very high} \)
• C. \( \text{Low} \)
• D. \( \text{Zero} \)

Hint:

Remember the key ideal characteristics of an op-amp, as they often appear in questions about ideal components. The concept of "infinite" or "zero" for these parameters helps simplify analysis and highlights the theoretical upper limits of performance. Specifically, for slew rate, "infinite" means the output can change infinitely fast, which is a key assumption for the op-amp to instantaneously respond to input changes without distortion, especially for high-frequency or large-amplitude signals.

Answer 1

The Correct Option is A

An ideal operational amplifier (op-amp) is a theoretical construct with several ideal characteristics that simplify circuit analysis and design. These ideal characteristics are typically assumed to simplify the understanding of basic op-amp circuits. One of the key ideal characteristics of an op-amp is its slew rate. The slew rate is the maximum rate of change of the output voltage of an op-amp, typically measured in volts per microsecond (V/µs). It describes how quickly the output can respond to large, rapid changes in the input signal. For an ideal op-amp, the output voltage is assumed to be able to change instantaneously in response to any change in the input signal, without any delay or limitation due to internal charging of capacitors or current limitations. Therefore, the slew rate of an ideal op-amp is considered to be infinite. Let's briefly review other ideal characteristics of an op-amp:

• Infinite Open-Loop Gain ($A_v \to \infty$): The output voltage is infinite for even a minuscule differential input voltage.
• Infinite Input Impedance ($Z_{in} \to \infty$): No current flows into the input terminals.
• Zero Output Impedance ($Z_{out} \to 0$): The op-amp can supply any amount of current to the load without a drop in output voltage.
• Infinite Bandwidth ($BW \to \infty$): The gain remains constant at all frequencies.
• Zero Input Offset Voltage ($V_{os} \to 0$): The output voltage is zero when the input voltage is zero.

In reality, practical op-amps have finite slew rates, finite gain, finite bandwidth, non-zero input bias currents, etc. However, for theoretical analysis of ideal op-amp behavior, an infinite slew rate is a fundamental assumption.