# US 5,703,849 A · Tracking servo correction control circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,703,849 A - Document ID: US5703849A - Status: Granted - Kind: A - Application number: 08/634,767 - Filed: 1996-04-19 - Granted: 1997-12-30 - Earliest claimed: 1995-04-28 - Assignees: Sony Corporation - Inventors: Hidenobu Noda - Web page: https://patentgrep.com/patent/US5703849A ## CPC - G11B 7/094: {Methods and circuits for servo offset compensation} - G11B 7/0948: {specially adapted for detection and avoidance or compensation of imperfections on the carrier, e.g. dust, scratches, dropouts (G11B7/095 takes precedence)} - G11B 7/0903: {Multi-beam tracking systems} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract In a tracking servo circuit for such as an optical disc device, and the like, a tracking error signal TE obtained in a servo-off state is subjected to A/D conversion, the center level thereof is calculated at a center level computation circuit, that value is stored in a register, at a time of servo-on, switches are connected to one terminal side, in the normal operation mode, the center level stored in the register is subtracted from the tracking error signal TE obtained at the time of the servo-on state at the subtraction circuit, the offset of the tracking error signal is corrected, and when light reflected from the surface of the disc can no longer be obtained due to an accidental cause, the connection of another switch is switched to the terminal b in response to the switching of the signal FOK generated based on the RF signal to the low level, and the offset correction operation of the tracking error signal TE is stopped. ## Claims ### Claim 1 A tracking servo circuit which obtains a drive output for correction of the position of the light irradiated on the surface of a recording medium by a tracking error signal obtained in accordance with the level of reflection of light irradiated to the surface of the medium, comprising: a first circuit which obtains a predetermined level of the tracking error signal obtained before the servo-on state is established from the start of driving; a register which holds said predetermined level of tracking error signal obtained by said first circuit; a second circuit which corrects said predetermined level of the tracking error signal obtained in the servo-on state based on said predetermined level held in said register; and a third circuit which stops the correction operation of said second circuit when a reflection light from the surface of the medium can no longer be obtained at the time of the servo-on state. ### Claim 2 (depends on 1) A tracking servo circuit as set forth in claim 1, wherein said first circuit comprises a subtraction circuit. ### Claim 3 (depends on 1) A tracking servo circuit as set forth in claim 1, wherein said second circuit is comprised by a subtraction circuit. ### Claim 4 (depends on 1) A tracking servo circuit as set forth in claim 1, further comprising a system control circuit which controls said third circuit based on said level of the tracking error signal. ### Claim 5 (depends on 4) A tracking servo circuit as set forth in claim 4, wherein said third circuit stopping the correction operation of said second circuit is switched by a switching means. ### Claim 6 (depends on 4) A tracking servo circuit as set forth in claim 4, wherein said third circuit is switched by a tracking level control signal and a tracking level disable signal from said system control circuit. ### Claim 7 (depends on 6) A tracking servo circuit as set forth in claim 6, wherein an RF signal is supplied to said third circuit to thereby control said switching operation. ### Claim 8 (depends on 7) A tracking servo circuit as set forth in claim 7, wherein said third circuit is controlled to stop the correction operation of said second circuit when said level of the RF signal is lowered than a predetermined level. ### Claim 9 (depends on 1) A tracking servo circuit as set forth in claim 1, wherein said predetermined level of the tracking error signal is set to as a center level of the tracking error signal. ### Claim 10 A tracking servo circuit which obtains a drive output for correction of the position of the light irradiated on the surface of a recording medium by a tracking error signal obtained in accordance with the level of reflection of light irradiated to the surface of the medium, comprising: a first circuit which obtains a predetermined level of the tracking error signal obtained before the servo-on state is established from the start of driving; a register which holds said predetermined level of tracking error signal obtained by said first circuit; a second circuit which corrects said predetermined level of the tracking error signal obtained in the servo-on state based on said predetermined level held in said register; a third circuit which stops the correction operation of the second circuit when a reflection light from the surface of the medium can no longer be obtained at the time of the servo-on state; and servo a filter circuit which inputs the output of said register via a means for switching. ### Claim 11 (depends on 10) A tracking servo circuit as set forth in claim 10, wherein said third circuit is controlled to stop the correction operation of said second circuit when a level of an RF signal is lowered than a predetermined level. ### Claim 12 (depends on 11) A tracking servo circuit as set forth in claim 11, wherein said third circuit stops said correction operation to prevent the application of the DC component contained in the tracking error signal to said servo filter circuit, so that a malfunction of said tracking servo is prevented.