Apparatus for reading an optically coded disc-shaped record carrier
First Claim
1. An apparatus for reading a disc-shaped record carrier with a multi-turn spiral information track provided with optically readable digitally coded information, said digital information being recorded in the information track as a stream of data bits of constant spatial bit frequency independently of the diameter of the track turn and comprising a sequence of detectable information blocks with a fixed number of data bits, said apparatus comprising a radiation source for emitting a read beam, an optical system for projecting said read beam as a read spot on the record carrier, a detection system for detecting the information contained in the read beam after cooperation with the record carrier, means for converting said information into an electric information signal, means for rotating the record carrier at a speed such that the read spot scans the information track at a scanning speed which is n times higher than the scanning speed which would result in said electric information signal having a desired bit frequency, a positioning system for controlling the radial position of the read spot on the record carrier, and a servo-system for controlling said scanning speed so that said electric information signal has a constant first bit frequency which is a factor n higher than the ultimately desired bit frequency independently of the radial position of the read spot on the record carrier, said converting means comprising a memory device for storing, with the first bit frequency, the data bits of an information block being read and for subsequently supplying said data bits with the desired bit frequency, to thereby reduce the susceptability of said apparatus to disturbances caused by shocks, vibrations and the like during read-out of the information, said apparatus further comprising a control unit which is coupled to the positioning system for effecting a jump-back of the scanning spot by one track pitch at instants which are determined by said control unit, said control unit also being coupled to the memory device for determining the periods during which said data bits are read into the memory device such that as a result of the scanning pattern of the information track and the read-in periods, consecutive information blocks are read into the memory device in accordance with a cycle which is determined by the control unit and are subsequently supplied by said memory device as a continuous sequence of information blocks.
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Accused Products
Abstract
The invention relates to an apparatus for reading a disc-shaped record carrier with a spiral information track in which an optically readable digitally coded information signal is recorded with a spatial bit frequency which is independent of the radius of the track turn. The scanning speed of the information track is selected to be a factor n higher than the scanning speed normally employed of the reproduction for the recorded information. By means of a memory device, information blocks being read and comprising a fixed number of data bits are time-expanded to restore the customary time relationship. A control unit determines the read-in cycles of the memory device for the storage of the information blocks being read and, via the radial positioning system for the read spot, it determines the scanning pattern of the record carrier so that the ultimately recorded information blocks are reproduced in the same sequence and at the desired rate.
33 Citations
7 Claims
- 1. An apparatus for reading a disc-shaped record carrier with a multi-turn spiral information track provided with optically readable digitally coded information, said digital information being recorded in the information track as a stream of data bits of constant spatial bit frequency independently of the diameter of the track turn and comprising a sequence of detectable information blocks with a fixed number of data bits, said apparatus comprising a radiation source for emitting a read beam, an optical system for projecting said read beam as a read spot on the record carrier, a detection system for detecting the information contained in the read beam after cooperation with the record carrier, means for converting said information into an electric information signal, means for rotating the record carrier at a speed such that the read spot scans the information track at a scanning speed which is n times higher than the scanning speed which would result in said electric information signal having a desired bit frequency, a positioning system for controlling the radial position of the read spot on the record carrier, and a servo-system for controlling said scanning speed so that said electric information signal has a constant first bit frequency which is a factor n higher than the ultimately desired bit frequency independently of the radial position of the read spot on the record carrier, said converting means comprising a memory device for storing, with the first bit frequency, the data bits of an information block being read and for subsequently supplying said data bits with the desired bit frequency, to thereby reduce the susceptability of said apparatus to disturbances caused by shocks, vibrations and the like during read-out of the information, said apparatus further comprising a control unit which is coupled to the positioning system for effecting a jump-back of the scanning spot by one track pitch at instants which are determined by said control unit, said control unit also being coupled to the memory device for determining the periods during which said data bits are read into the memory device such that as a result of the scanning pattern of the information track and the read-in periods, consecutive information blocks are read into the memory device in accordance with a cycle which is determined by the control unit and are subsequently supplied by said memory device as a continuous sequence of information blocks.
Specification