Velocity correction circuit for video discs
AssigneeRCA Corporation
InventorThomas William Burrus
Life of this patent
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Abstract
Velocity and phase errors in signals derived from a rotating video disc are minimized with the use of a voltage controlled oscillator and an electromechanical transducer. A control circuit employing an active and a passive filter maintains an appropriate frequency response to the voltage controlled oscillator and electromechanical transducer in order to appropriately share a single controlling error signal.
Claims5
In a video disc player in which a signal pickup stylus cooperates with a signal information storing groove of a disc subject to rotation at a given rotational frequency, said information storing groove including recorded luminance, chrominance and color synchronization signal components, and said signal components as recovered by said pickup stylus being subject to frequency errors as a consequence of errors in the velocity of relative motion between said disc groove and said pickup stylus, apparatus for providing correction of said signal component errors comprising:
- means coupled to said signal pickup stylus for providing video signals from information recorded on said video disc;
- a voltage controlled oscillator providing oscillations of controllable frequency;
- heterodyning means responsive to said video signals and said oscillations for frequency translating said video signals;
- a reference oscillator;
- phase detecting means responsive to a frequency translated color synchronization component derived from said heterodyning means and to an output of said reference oscillator for providing error signals;
- means for supplying said error signals to said voltage controlled oscillator to provide, over a range of error signal frequencies, an adjustment of the frequency of said oscillations in a sense opposing departures from frequency correspondence between said reference oscillator output and said frequency translated color synchronization component;
- a transducer coupled to said signal pickup stylus for repositioning said stylus along said video disc groove in response to electrical signals;
- means for rendering said transducer responsive to error signals from said phase detecting means in a sense opposing said errors in velocity of relative motion;
- said last-named means including an error signal amplifier having a input and an output, means providing a direct current coupling for error signal information between said phase detecting means and said error signal amplifier input, additional means providing a direct current coupling for error signal information between said error signal amplifier output and said transducer, and frequency selective means coupled to said error signal amplifier for shaping the frequency response characteristic thereof in a manner effectively restricting the the velocity error opposition provided by said transducer to a relatively narrow low frequency portion of said error signal frequency range, said portion encompassing error signal frequencies inclusive of said rotational frequency;
- and
- means coupled between the output of said error signal amplifier and said voltage controlled oscillator for augmenting the error signal applied thereto by said first-named error signal supplying means, said error signal augmenting means having a frequency response characteristic effectively confining said augmentation to a narrow segment of said low frequency range portion below said rotational frequency.
In a video disc player in which a signal pickup stylus cooperates with a signal information storing groove of a disc subject to rotation at a given rotational frequency to recover recorded composite video signals including luminance, chrominance and color synchronization signal components, and wherein said recovered signal components are undesirably subject to frequency errors as a consequence of deviations from a desired velocity of relative motion between said disc groove and said pickup stylus, correction apparatus comprising:
- means coupled to said stylus for developing composite video signals representative of information stored in said video disc groove;
- a voltage controlled oscillator providing oscillations of a controllable frequency;
- heterodyning means responsive to said oscillations and said developed signals for frequency translating said developed signals;
- a reference oscillator;
- an arm stretcher transducer coupled to said stylus for imparting motion to said stylus along said groove in response to signals applied thereto;
- means for phase comparing signals from said reference oscillator with a color synchronization component of said frequency translated signals to develop error signals indicative of departures from frequency correspondence therebetween;
- means, having a first frequency response characteristic, for supplying said error signals from said phase comparing means to said voltage controlled oscillator to establish a first component frequency error correction loop;
- and
- means, coupled to said phase comparing means and having a second frequency response characteristic, for supplying said error signals to said arm stretcher transducer to establish a second component frequency error correction loop;
- said first frequency response characteristic differing from said second frequency response characteristic in such manner that correction of frequency errors which recur at said rotational frequency is predominately effected by said second correction loop to the substantial exclusion of said first correction loop, whereas said first correction loop provides significant correction of errors which recur at frequencies in a narrow range below said rotational frequency.
Dependencies are inferred from the claim text.