By Mark Stansberry, updated Mar 24, 2022
Slew rate – the rate of voltage change per unit time – quantifies how quickly a circuit can transfer information. High slew rates enable faster data transmission, which is why cutting‑edge processors and communication modules are built around components with the highest specified slew rates. Calculating the slew rate is straightforward: simply divide the voltage difference by the elapsed time between those voltage levels.
Begin with a voltage‑vs‑time trace of the component under study. Most manufacturers provide this information in the device datasheet. If not, capture the waveform with an oscilloscope or equivalent measurement system.
Identify the region where the signal rises from its minimum to its maximum. Note the peak voltage and the valley voltage on the vertical axis, and record the corresponding times on the horizontal axis. For example, a low voltage of 0 V at 1 s and a high voltage of 5 V at 4 s.
Subtract the lowest voltage from the highest:
5 V – 0 V = 5 V
Subtract the time of the low voltage from the time of the high voltage:
4 s – 1 s = 3 s
Divide the voltage change by the time change:
5 V ÷ 3 s ≈ 1.66 V/s
The slew rate is a key indicator of how rapidly an amplifier or digital logic circuit can transition from a low to a high voltage state. In high‑speed digital systems, rise times can be as short as a few nanoseconds, which translates to slew‑rate specifications ranging from 10^6 V/s to 10^9 V/s.
Designers typically use the 10 % and 90 % voltage levels rather than the absolute minimum and maximum to define rise or fall times. The interval between the 10 % and 90 % points is the effective rise time used in precise slew‑rate calculations.
