Explain slew rate and its impact on large-signal performance.

• A. Slew rate is the maximum rate of change of the input voltage.
• B. Slew rate is the maximum rate of change of the output voltage (V/µs); insufficient SR causes waveform distortion for fast-changing inputs, especially square waves.
• C. Slew rate is the ratio of output to input frequency.
• D. Slew rate is the noise density of the amplifier.

Answer: (B)

Slew rate describes how fast the output voltage can change in response to a rapid input change. It is the maximum dVout/dt, usually given in volts per microsecond, and it comes from the amplifier’s internal limits, such as the current available to charge or discharge the compensation capacitor. In large-signal scenarios, when you drive the amplifier with fast edges or large amplitudes (think of a square wave), the output can’t rise or fall instantly; it can only slope at a finite rate. If the required slope to reproduce the input edge exceeds the device’s slew rate, the output waveform becomes distorted—the transitions are rounded or sloped rather than sharp, and the peak amplitude during the transition can be reduced. This effect is most noticeable for fast-changing inputs like square waves because those edges demand the greatest dV/dt. To improve large-signal performance, you’d use an amplifier with a higher slew rate, or slow down the input edges or reduce the input amplitude, accepting trade-offs in bandwidth or speed.