Slew rate (SR) is the maximum rate of change an op-amp's output can physically achieve, typically specified in volts per microsecond (V/µs). It is a completely separate limitation from the op-amp's small-signal bandwidth (gain-bandwidth product): small-signal bandwidth describes how well the op-amp tracks small fast signals, while slew rate limits how fast the output can swing through a large voltage change, regardless of frequency response on paper.
A sine wave's fastest rate of change happens as it crosses zero, and that peak rate of change is proportional to both its frequency and its amplitude: d/dt[Vpeaksin(2πft)] has a maximum of 2πfVpeak. If this required rate exceeds the op-amp's slew rate, the amplifier physically cannot keep up, and the output distorts into a triangle-wave-like shape instead of following the intended sine — this is exactly why a large-amplitude high-frequency signal can distort even on an op-amp whose small-signal bandwidth looks more than adequate.
The frequency at which this just starts to happen, for a given amplitude, is called the Full Power Bandwidth (FPBW): the highest frequency at which the op-amp can still deliver its full rated output swing without slew-induced distortion.
| Quantity | Formula |
|---|---|
| Full power bandwidth | FPBW = SR/(2πVpeak) |
| Slew rate required for a target f, Vpeak | SRrequired = 2πfVpeak |
| Peak rate of change of a sine wave | dV/dt|max = 2πfVpeak (at the zero crossing) |
| Typical general-purpose op-amp SR | 0.5–20 V/µs (e.g. classic 741-class parts) |
| Typical high-speed op-amp SR | 50–1000+ V/µs (video/RF-oriented parts) |
It is the maximum rate of change (in volts per microsecond) an op-amp's output can physically achieve, independent of frequency — a hard physical limit set by the internal circuit's ability to charge/discharge its compensation capacitance.
FPBW is the highest sine-wave frequency at which an op-amp can still deliver its full rated output amplitude without slew-rate-induced distortion, calculated as FPBW=SR/(2πVpeak).
The peak rate-of-change of a sine wave is proportional to both frequency and amplitude (2πfVpeak). A small-amplitude signal at the same frequency requires a much lower slew rate to follow cleanly, so it may stay well under the op-amp's slew rate limit even when a larger-amplitude signal at that same frequency would exceed it.
No. GBW describes small-signal frequency response (how gain falls off with frequency for small signals), while slew rate is a large-signal limitation on how fast the output voltage can physically change. An op-amp can have excellent GBW yet still slew-limit badly on large signals if its SR spec is comparatively low.
Instead of a smooth sine wave, the output becomes visibly triangular, with straight, constant-slope ramps (at the maximum slew rate) replacing the natural curved sine shape near the zero crossings and peaks.
Use SRrequired=2πfVpeak, where f is your highest frequency of interest and Vpeak is the largest output amplitude you need at that frequency, then choose an op-amp with a rated slew rate comfortably above this (commonly with 2× or more margin).
General-purpose op-amps (like classic 741-derived designs) are often 0.5–20 V/µs; "high-speed" or "video" op-amps commonly reach 50–1000+ V/µs. What counts as "fast enough" always depends on your specific frequency and amplitude requirements, not an absolute number.
Yes, in fact even more directly — a fast edge on a square wave or pulse demands an extremely high instantaneous rate of change, and an op-amp's slew rate directly limits how fast that edge can actually rise or fall, rounding off otherwise-sharp transitions.
Because the relevant number is the required rate at full amplitude across the whole audio band, not just at the highest frequency component alone, and some designs intentionally include margin for ultrasonic content, transients, and feedback stability that pushes effective bandwidth requirements above 20 kHz.
No — slew rate is a fundamental limitation of the op-amp's internal output stage and compensation, and it doesn't change based on the external feedback network or closed-loop gain configuration; the only way to get more slew rate is to choose a faster op-amp.
FPBW marks the theoretical onset of slew-induced distortion, so operating exactly at it, or especially above it, risks visible waveform distortion; a common design practice is to keep your actual operating frequency well below the calculated FPBW for margin, rather than treating it as a hard, distortion-free ceiling.
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