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Tracking error signal detector

  • US 5,808,979 A
  • Filed: 11/22/1995
  • Issued: 09/15/1998
  • Est. Priority Date: 11/25/1994
  • Status: Expired due to Term
First Claim
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1. An apparatus for detecting a tracking error signal from recorded bit information of a high density optical record carrier on which a laser beam is emitted to a data track area to produce a reflection beam carrying the recorded bit information on the optical record carrier, said apparatus comprising:

  • a divided photodetector having a first divided portion and a second divided portion disposed in a light path of the reflection beam from the optical record carrier, said divided photodetector producing a first photodetector signal from said first divided portion and a second photodetector signal from said second divided portion, wherein said first photodetector signal and said second photodetector signal both contain the recorded bit information;

    a phase comparison means for detecting a phase difference between said first and said second photodetector signals, and for producing a phase difference signal which is a tracking error signal;

    a first low-order phase lead filter located between said first divided portion and said phase comparison means for amplifying a high frequency component of said first photodetector signal and shifting a phase of the high frequency component of said first photodetector signal; and

    a second low-order phase lead filter located between said second divided portion and said phase comparison means for amplifying a high frequency component of said second photodetector signal and shifting a phase of said high frequency component of said second photodetector signal in substantially a same amount and in a same direction as the high frequency component of said first low-order phase lead filter;

    wherein said first and second low-order phase lead filters are characterized by a transfer function G=Go (1+jf/f5), wherein Go is a gain and f5 is a cut-off frequency which is set at an approximate middle of a frequency band of the recorded bit information.

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