Signal level detecting circuits.

摘要

A signal level detecting circuit comprises an input terminal (33) to which an input signal (Sc) with level variations is applied, a level comparator (31) operative to compare the level of the input signal (Sc) with the level of a reference signal (Sw) variable in level and to produce a comparison output signal (Po) having first and second levels in response 16 to differences between the level of the input signal and the level of the reference signal, a control signal generator (11) operative to produce control signals one of which is obtained when a period of time in which the comparison output signal has the first level is not longer than one of two different reference periods of time and the other of which is obtained when the period of time in which the comparison output signal has the first level is not shorter than the other of two different reference periods of time, a pulse generator (13) operative to produce a pulse signal having its pulse duty factor varied in response to the control signals obtained from the control signal generator (11), and an integrator (29) operative to produce an integration output signal based on the pulse signal obtained from the pulse generator (13) and to supply the level comparator (31) with the integration output signal as the reference signal.