Abstract: A synchronizing signal reproducing circuit in a disc playback device for playing back discs such as a video disc and Compact Disc comprises an assumed synchronizing signal detection circuit for taking out an assumed synchronizing signal having possibility of being a true synchronizing signal from a signal reproduced from a disc, a window establishing circuit for establishing a window which, on the basis of a preceding true synchronizing signal, includes a timing at which a true synchronizing signal is expected to occur, and a synchronizing signal picking up circuit for picking up the assumed synchronizing signal as a true synchronizing signal if it occurs in the window. The window is so established that a future side range becomes wider than a past side range with respect to the timing at which the true synchronizing signal is expected to occur.

Abstract: In one aspect of the invention, a disc motor control circuit in a disc playback device comprises a rotation detection circuit for detecting the rotation speed of a disc motor and producing a rotation detection signal, a first control circuit for controlling the rotation speed of the disc motor by comparing the rotation detection signal with a reference clock, a second control circuit for controlling the rotation speed of the disc motor by comparing a synchronizing signal taken out of a reproduced signal from the disc with a reference clock, a window circuit for establishing a window for an expected timing of a next synchronizing signal on the basis of the synchronizing signal taken out of the reproducing signal, a state detection circuit for detecting a state of rotation of the disc motor by counting the number of the synchronizing signal entering the window and a mode switching circuit for selectively operating one of these control circuits in accordance with the result of counting in the state detection cir