Global Standards for the Microelectronics Industry
fall time (tf) (1) (general)
The time interval between one reference point on a waveform and a second reference point of smaller magnitude on the same waveform.
NOTE The first and second reference points are usually 90% and 10%, respectively, of the steady‑state amplitude of the waveform existing before the transition, measured with respect to the steady‑state amplitude existing after the transition.
(2) (of an analog integrated circuit): For a step-function change of the input signal level, the time interval between the end of the delay time (normally 90%) and that instant at which the magnitude of the output signal first passes through a specified value (normally 10%) close to its final value. (Ref. IEC 747‑3.)
(3) (of a digital integrated circuit): Synonym for "transition time, high-to-low level".
(4) (of a transistor): (A) The time interval during which the amplitude of the trailing edge of a pulse decreases from 90% to 10% of its maximum amplitude.
(B) Synonym for "current fall time, tfi".