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. These values may be expressed as
ratios or, equivalently, as
percentages respect to a given reference value. In
analog or
digital electronics, these percentages are commonly the 10
nd 90% (or equivalently and ) of the output step height: however, other values are commonly used. For applications in control theory, according to , rise time is defined as "
the time required for the response to rise from to of its final value", with 0% to 100% rise time common for underdamped second order systems, 5% to 95 or critically damped and 10% to 90 or overdamped ones. According to , the term "rise time" applies to either positive or negative
step response, even if a displayed negative excursion is popularly termed
fall time.