Turntable rotational speed and phase control system for a video disc

Abstract

Video disc play/record apparatus includes a turntable driven by a uni-directional DC motor, a speed loop for controlling motor rotation responsively to horizontal sync signal and a position loop for controlling the rotational phase of the turntable responsively to a frame sync signal. The speed loop comprises a motor driven tachometer whose output is stabilized by a phase locked loop about a nominal frequency. A phase and frequency difference detector, responsive to the phase locked loop output and the horizontal sync signal, provides a driving voltage to power amplifiers coupled to the motor. The position loop includes means cooperating with the speed loop to regulate the turntable phase of rotation responsively to the phase difference between the outputs of a turntable tachometer and a frame and vertical sync signal source. Delay circuits in the speed and position loops provide compensation for detected disc mounting error between a previous recording mounting position and the current mounting position of the disc on the turntable. A by-pass circuit directly powers the motor during start-up operations. Stopping and overspeed protection are accomplished by inhibiting the power amplifiers and coupling a source of reverse potential to the motor.