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Op-Amp Slew Rate
The maximum rate at which an op-amp's output voltage can change, limiting large-signal high-frequency response.
Interpretation
Slew rate SR = ΔV_out/Δt is the maximum rate at which the op‑amp's output voltage can change.
It limits the large‑signal bandwidth and causes distortion if exceeded.
Example: SR=0.5V/µs means the output can change 0.5V per microsecond; a 10V swing takes at least 20µs.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| SR | Slew rate | V/µs |
| ΔV_out | Change in output voltage | V |
| Δt | Change in time | µs |
What it means
The slew rate (SR) of an operational amplifier is the maximum rate of change of the output voltage, defined as SR = ΔV_out/Δt, typically measured in V/µs. It is limited by the internal compensation capacitor and the available current. If the input signal demands a faster output change than the slew rate, distortion occurs (e.g., triangular wave output for a square wave input). Slew rate determines the large‑signal bandwidth and is a key specification for high‑frequency applications. Example: An op‑amp with SR=0.5V/µs can change its output by 0.5V in 1µs. To produce a 10V peak‑to‑peak sine wave at a frequency f, the required slew rate is π·V_pp·f. If f=100kHz and V_pp=10V, the required SR = π*10*100k = 3.14 V/µs, which exceeds 0.5V/µs, causing distortion.
Worked example
Op‑Amp Slew Rate – Practical Example
Real‑World| Parameter | Value |
|---|---|
| ΔVout | 5 V |
| Δt | 1 µs |
| Formula | SR = ΔVout / Δt |
Common mistakes
Watch unit consistency and the assumptions behind the formula; misapplying it outside its valid conditions is the most frequent error.Applications
Op‑amp slew rate SR = ΔV_out/Δt is the maximum rate of change of the output voltage. It limits the full‑power bandwidth and can cause distortion if exceeded. Engineers use it to select op‑amps for high‑speed applications, to estimate distortion, and to design circuits with adequate bandwidth. Slew rate is a key parameter for audio, video, and high‑speed signal processing.
- High‑speed amplifier selection and design
- Audio and video signal processing
- Pulse and waveform generation circuits
- Data acquisition and ADC driver design
- Educational understanding of op‑amp limitations
Frequently Asked Questions
Slew rate is the maximum rate of change of the output voltage of an op‑amp: SR = ΔV_out / Δt. It is typically expressed in V/µs. It limits the large‑signal frequency response.
If the required output slew rate exceeds the op‑amp's slew rate, the output will be distorted (triangular waveform instead of sinusoidal). It sets the maximum frequency for a given output amplitude.
For a sinusoidal output V_out = V_p sin(2πft), the maximum slew rate is SR_max = 2πf V_p. Thus, the maximum frequency is f_max = SR / (2π V_p).
µA741: ~0.5 V/µs; LM358: ~0.3 V/µs; high‑speed op‑amps: >1000 V/µs.
Common errors: 1) using the small‑signal bandwidth (which assumes small signals), 2) forgetting the factor of 2π, 3) applying to DC signals (where slew rate is not a limitation), 4) ignoring capacitive loading.
If the signal exceeds the slew rate, the output will be rate‑limited, causing harmonic distortion. This is especially problematic for high‑frequency, high‑amplitude signals.
Bandwidth is the small‑signal frequency response (linear); slew rate is the large‑signal limit (non‑linear). Both are important.
Audio power amplifiers, high‑speed data acquisition, and video signal processing.