Rise time

In electronics, when describing a voltage or current step function, rise time is the time taken by a signal to change from a specified low value to a specified high value.^[1] These values may be expressed as ratios^[2] or, equivalently, as percentages^[3] with respect to a given reference value. In analog electronics and digital electronics,^{[citation needed]} these percentages are commonly the 10% and 90% (or equivalently 0.1 and 0.9) of the output step height:^[4] however, other values are commonly used.^[5] For applications in control theory, according to Levine (1996, p. 158), rise time is defined as "the time required for the response to rise from x% to y% of its final value", with 0% to 100% rise time common for underdamped second order systems, 5% to 95% for critically damped and 10% to 90% for overdamped ones.^[6]

Similarly, fall time (pulse decay time) ${\displaystyle t_{f}}$ is the time taken for the amplitude of a pulse to decrease (fall) from a specified value (usually 90% of the peak value exclusive of overshoot or undershoot) to another specified value (usually 10% of the maximum value exclusive of overshoot or undershoot). Limits on undershoot and oscillation (also known as ringing and hunting) are sometimes additionally stated when specifying fall time limits.

According to Orwiler (1969, p. 22), the term "rise time" applies to either positive or negative step response, even if a displayed negative excursion is popularly termed fall time.^[7]