| 摘要 |
<p>This invention relates to an improvement in a video signal playback device which derives video signals from an information track on a video disc using a light beam source for impinging upon an information track on the surface of the video disc. In prior art devices of this type, the circuitry necessary to sense whether or not a light beam is on or off track is rather complicated, since it has been necessary to have at least two sensors (and in some instances three sensors), together with the associated electronics to perform the necessary feedback function for maintaining accurate tracking of the reading beam as the reader and disc move relative to one another radially of the disc. The present invention overcomes this difficulty by providing a simplified single beam tracking system including circuitry which is responsive to the position of the impinging light beam relative to a prescribed edge portion of the information track. When the light beam impinges the prescribed edge portion of the track, the output from the circuitry is nil. The circuitry provides an output voltage having a first polarity when the light beam impinges less than the prescribed edge portion, and a second polarity when the light beam impinges more than the prescribed edge portion. When the output voltage signal is applied to the tracking control device, a closed loop tracking system results, accurately keeping the light beam impinging on the prescribed edge portion of the track.</p> |
