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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.〔According to the , p. R-22).〕 These values may be expressed as ratios〔See for example , and .〕 or, equivalently, as percentages〔See for example , and .〕 respect to a given reference value. In analog or digital electronics, these percentages are commonly the 10% and 90% (or equivalently and ) of the output step height:〔See for example , and .〕 however, other values are commonly used.〔For example state that "''For some applications it is desirable to measure rise time between the 5 and 95 per cent points or the 1 and 99 per cent poins.''".〕 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% for critically damped and 10% to 90% for overdamped ones.〔Precisely, states: "''The rise time is the time required for the response to rise from x% to y% of its final value. For overdamped second order systems, the 0% to 100% rise time is normally used, and for underdamped systems'' (...) ''the 10% to 90% rise time is commonly used''". However, this statement is incorrect since the 0%–100% rise time for an overdamped 2nd order control system is infinite, similarly to the one of an RC network: this statement is repeated also in the second edition of the book .〕 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.〔Again according to .〕
== Overview ==
Rise time is an analog parameter of fundamental importance in high speed electronics, since it is a measure of the ability of a circuit to respond to fast input signals.〔According to , "''The most important characteristics of the reproduction of a leading edge of a rectangular pulse or step function are the rise time, usually measured from 10 to 90 per cent, and the "overshoot"''". And according to , "''The two most significant parameters in the square-wave response of an amplifier are its rise time and percentage tilt''".〕 Many efforts over the years have been made to reduce the rise times of generators, analog and digital circuits, measuring and data transmission equipment, focused on the research of faster electron devices and on techniques of reduction of stray circuit parameters (mainly capacitances and inductances). For applications outside the realm of high speed electronics, long (compared to the attainable state of the art) rise times are sometimes desirable: examples are the dimming of a light, where a longer rise-time results, amongst other things, in a longer life for the bulb, or in the control of analog signals by digital ones by means of an analog switch, where a longer rise time means lower capacitive feedthrough, and thus lower coupling noise to the controlled analog signal lines.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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