Definitions for "Fall Time"
The time for the amplitude of system response to decay to 37% of its steady-state value after the removal of a steady-state step input signal.
Fall time is defined as the transition time from an output logic high to an output logic low and is measured in nanoseconds (nSec). This transition time is measured at specified voltage thresholds or at specified percentages of the output waveform amplitude. See rise time.
The time required for a signal to change from a high level (usually 90%) to a low level (usually 10%) of its base line-to-peak or peak-to-peak amplitude. (Also, see Rise Time.)
Keywords:  switching, speed, see
See Switching Speed