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Op-Amp Slew Rate & Full-Power Bandwidth

Calculate op-amp full-power bandwidth from slew rate and signal amplitude, and verify the op-amp can handle your signal without slew-rate distortion.

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Formula

FPBW = SR / (2π × V_peak)

SR— Slew rate (V/μs)
V_peak— Peak output voltage (V)

How It Works

Slew rate (SR) is the maximum rate at which an op-amp's output voltage can change, expressed in V/μs. It is determined by the charging current available to the compensation capacitor inside the op-amp. When a large-amplitude, high-frequency signal demands a faster voltage change than the op-amp can supply, the output becomes a triangle wave instead of a sine wave — a nonlinear distortion called slew-rate limiting. The Full-Power Bandwidth (FPBW) is the highest frequency at which the op-amp can produce an undistorted full-amplitude sinusoidal output: FPBW = SR / (2π × V_peak). The minimum slew rate required to handle a signal of frequency f and peak amplitude V_p without distortion is SR_min = 2π × f × V_p (in V/μs, divide by 10⁶). Audio op-amps must handle 20 kHz signals; at ±10 V output, SR_min = 2π × 20000 × 10 / 10⁶ ≈ 1.26 V/μs.

Worked Example

Op-amp: NE5532, SR = 9 V/μs. Signal: 20 kHz, 5 V peak. Minimum slew rate required: SR_min = 2π × 20000 × 5 / 10⁶ = 0.628 V/μs SR margin = 9 − 0.628 = 8.37 V/μs (adequate) Full-power bandwidth: FPBW = 9 × 10⁶ / (2π × 5) = 286,479 Hz ≈ 286 kHz The NE5532 can handle a 5 V peak signal up to 286 kHz without slew limiting — far beyond audio. However, if used at ±15 V supply (V_peak = 13.5 V at 90% rail): SR_min for 20 kHz = 2π × 20000 × 13.5 / 10⁶ = 1.70 V/μs FPBW = 9 × 10⁶ / (2π × 13.5) = 106 kHz — still sufficient for audio.

Practical Tips

  • ✓For audio circuits with ±15 V rails and a 20 kHz signal, SR > 2 V/μs is the absolute minimum; use > 5 V/μs for headroom. The NE5532 (9 V/μs) and OPA2134 (20 V/μs) are popular audio choices with adequate slew margin.
  • ✓High-speed video or RF op-amps (SR 100+ V/μs) are not always better in audio — they can be noisier and more prone to instability at audio-frequency closed-loop gains. Match the op-amp to the bandwidth actually needed.
  • ✓Slew-rate distortion sounds harsh and buzzy, distinctly different from harmonic distortion. If an op-amp stage sounds harsh at high volumes, measure the output waveform at 20 kHz on a scope to check for triangular clipping.

Common Mistakes

  • ✗Confusing gain-bandwidth product (GBW) with slew rate — GBW applies to small-signal bandwidth under closed-loop conditions. Slew rate is a large-signal, nonlinear limitation. A fast GBW op-amp can still slew-limit on a large-amplitude, high-frequency signal.
  • ✗Forgetting to account for actual peak amplitude — the slew rate requirement scales directly with peak amplitude. An op-amp with FPBW of 100 kHz at ±10 V peak has a FPBW of only 50 kHz at ±20 V peak.
  • ✗Selecting an op-amp with exactly SR = SR_min — always apply a design margin of at least 2× (6 dB), especially in audio applications where harmonics and transients can demand instantaneous slew rates exceeding the fundamental's requirement.

Frequently Asked Questions

SR_min = 2π × 20000 × 12 / 10⁶ ≈ 1.51 V/μs. With a 2× safety margin, target ≥ 3 V/μs. Most modern audio op-amps (NE5532: 9 V/μs, TL072: 13 V/μs) comfortably exceed this.
Yes. DAC output buffer op-amps must pass 20 kHz audio after the reconstruction filter, but the reconstruction filter itself may produce sub-microsecond transients at the Nyquist frequency (22.05 kHz for 44.1 kHz audio). Choose buffer op-amps with SR > 10 V/μs to handle these transients cleanly.
At signal levels that approach but don't reach the slew-rate limit, the op-amp produces 'soft slew-rate limiting' — a form of gentle nonlinearity that increases THD before obvious waveform clipping is visible. To keep THD below 0.001% at 20 kHz, design for SR at least 3–5× above SR_min.

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