Op-Amp Slew Rate Limit

Formula

Description

The slew rate of an op-amp limits the maximum frequency at which it can produce a full-amplitude sinusoidal output without distortion. The maximum rate of change of a sine wave occurs at the zero crossing and equals 2π × f × Vpk. If this exceeds the op-amp's slew rate, the output becomes triangular rather than sinusoidal, introducing severe harmonic distortion. This frequency limit is called the full-power bandwidth and is often much lower than the small-signal bandwidth specified by GBW.

Variables

• fmax — Maximum undistorted frequency (Hz)
• SR — Op-amp slew rate (V/s)
• Vpk — Peak output voltage amplitude (V)

Practical Notes

Common slew rates: LM358 0.5 V/µs, TL072 13 V/µs, OPA2134 20 V/µs, AD8065 180 V/µs. For audio applications with ±10V output at 20 kHz, minimum SR = 2π × 20000 × 10 = 1.26 V/µs. Always provide margin: use at least 5-10x the minimum required slew rate for low-distortion audio.