Optical Disc Corporation

W Ray Dakin

John F Browne

A videodisc recorder signal processing system and a recording method providing programmed control of the amplitude of the secondary (audio channel) carrier signals relative to the primary (video channel) carrier signal during recording. In one embodiment, the amplitude of the two audio carrier signals are varied in accordance with a preprogrammed profile to counteract the MTF effects of the recording system. In another embodiments, the amplitudes of the two audio carriers are varied in accordance with a preprogrammed pattern related to the relative criticality of the audio and video information recorded on the disc. The signal characteristics of the audio channels are improved by increasing the amplitude of the audio carriers. When no audio information exists, the audio carrier signals are substantially eliminated to maximize the quality of the video channel. At other times, the audio carrier signals are decreased to improve the video quality by reducing IM products.

Audio carrier amplitude control for videodisc recorder

A modulator including a voltage controlled oscillator (VCO) having its center frequency stabilized to a reference frequency using a phase locked loop in which the low frequency range is increased by using frequency translation techniques. The VCO output signal is translated relative to the phase locked loop feedback signal so that an increased frequency division ratio can be used in the feedback loop and the effective frequency deviation at the phase comparator can be reduced by an arbitrary factor. This has the effect of increasing the allowable deviation at a given information signal frequency by that arbitrary factor. Likewise, a given deviation can be maintained for input information frequencies which are an arbitrary fraction of the low end cutoff frequencies of conventional modulators.

PLL stabilized frequency modulator with extended low frequency range

A focus control system with a novel gain control circuit for continually varying the gain of the focus error signal based on the optical characteristics of the medium. As those optical characteristics change to decrease the amount of light available to the focus error detector, the gain of the focus error signal is increased so that the overall gain of the servo loop and the overall response of the servo to a focus error remains constant. This is accomplished by monitoring the optical characteristics of the medium which affect the focus error detector. In a multiple detector system, the outputs of all of the detectors are summed together. The resultant signal is a reflectivity or a transparency signal and is used in a novel circuit for controlling the servo gain.

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Huntington Beach, CA, United States of America

W Ray Dakin