Periodically biased video disc player servo system

In a video disc player of the kind including a video signal correction servo system comprising a reference oscillator for producing a reference signal, a phase detector responsive to an enabling signal for comparing said reference signal with a color burst component of a video signal produced by said player and producing an error voltage representative of deviations of said color burst component from a prescribed relationsip with said reference signal, an error voltage holding capacitor for storing said error voltage during a portion of each horizontal scan interval of said video signal, a feedback path for supplying said error voltage to at least one point in said player in a sense to minimize said deviations, the improvement for periodically biasing said video signal correction servo system to a predetermined point within its control range, said improvement comprising:

• a precharging circuit means coupled to said error voltage holding capacitor and responsive to a control signal for charging said error voltage holding capacitor to a predetermined voltage level when said control signal is present;
• and
• a timing circuit means synchronized with a horizontal synchronizing signal derived from said video signal for supplying said enabling signal to said phase detector and simultaneously supplying said control signal to said precharging circuit means during a first time interval, for supplying said enabling signal to said phase detector and simultaneously terminating said control signal during a second time interval subsequent to said first time interval and for terminating both said enabling signal and said control signal during a third time interval subsequent to said second time interval.

In a video disc player of the kind comprising a turntable for rotating a video disc, a pickup transducer proximate said disc for producing capacitance variations representative of information recorded on said disc as a frequency modulated carrier in BSC format, a pickup converter responsive to said capacitance variations for producing a voltage output signal, a demodulator for demodulating said FM output signal to produce a composite video signal, a video converter for converting said composite video signal from said BSC format to an NTSC format, a phase detector responsive to a keying signal for producing a composite error signal representative of phase and frequency errors between the output signal of an NTSC reference frequency crystal oscillator and the color burst component of an NTSC chrominance output signal produced by said video converter, an error voltage holding capacitor for storing said composite error signal, a filter for separating the composite error signal into first and second components, an arm stretcher transducer responsive to said first component and coupled to said pickup transducer for varying the position of said pickup transducer in a sense to minimize frequency errors in both the chrominance and luminance components of said composite video output signal produced by said video converter and a voltage controlled crystal oscillator in said video converter responsive to said second component of said composite error signal for correcting phase and frequency errors of solely the chrominance component of said NTSC composite video output signal, the improvement, comprising:

• a precharging circuit means coupled to said error voltage holding capacitor and responsive to a control signal for charging said error voltage holding capacitor to a predetermined voltage level when said control signal is present;
• and
• a timing circuit means synchronized with the tip of a horizontal synchronizing pulse derived from said video converter for supplying said keying signal to said phase detector during first and second time intervals and terminating said keying signal during a third time interval, said timing circuit means supplying said control signal to said precharging circuit means during said first time interval and terminating said control signal during said second and third time intervals.