risetime

Rise time, sometimes written risetime, is the time required for a signal or waveform to transition from a specified low value to a specified high value. In electronics, the common convention is from 10% to 90% of the final amplitude, although other thresholds such as 20–80% or 0–100% are used in different contexts. Rise time is a key indicator of how quickly a circuit can respond to changes and is significant for both digital and analog systems.

Rise time definitions are often tied to the edge of a pulse or step. The exact thresholds used can affect comparisons between devices, and some specifications report 10–90% or 20–80% rise times. In digital logic, the rise time of a signal edge influences timing budgets, data integrity, and the overall speed of a logic family or interconnect.

Rise time is closely related to bandwidth. For many simple, single-pole systems, rise time is approximately tr ≈ 0.35/BW, with BW representing the system bandwidth (3 dB). Thus, higher bandwidth allows faster edges. However, in real circuits, factors such as source and load impedance, parasitic capacitance, and the drive strength of the output stage determine the achievable rise time.

Measurement and interpretation can be affected by the testing setup. Probe and cable capacitances, termination, and input/output impedances can artificially slow observed edges, so de-embedding or corrections are often necessary to estimate the intrinsic rise time of a device. Related concepts include slew rate, which describes the maximum rate of change of voltage, and signal integrity phenomena such as overshoot and ringing.