Arrangement for reproducing data readable by an optical scanner from tracks of a recorded medium

• US 4,888,754 A
• Filed: 04/29/1988
• Issued: 12/19/1989
• Est. Priority Date: 05/09/1987
• Status: Expired due to Term

• Current Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Original Assignee: Deutsche Thomson-Brandt Gmbh (Vantiva SA)
• Inventors: Gleim, Gunter
• Primary Examiner(s): Richardson, Robert L.
• Application Number:
  US07/188,459
• Time in Patent Office: 599 Days
• Field of Search: 369/32, 369/43-47, 358/342, 250/201 DF, 318/640
• US Class Current: 369/44.11
• CPC Class Codes: G11B 7/0909 by astigmatic methods
• CPC Class Codes: G11B 7/094 Methods and circuits for servo offset compensation

Abstract

An arrangement for reproducing data readable by an optical scanner from tracks on a recorded medium. At least one beam of light is focused onto the medium, and the beam is positioned along the tracks by a tracking control. The recorded medium reflects the beam onto a photodetector which generates an electrical data signal having a phase relation, a focusing error signal also having a phase relation for indicating the current state of the focus control. A tracking error signal also supplied by the photodetector indicates the current state of the tracking control. A control amplifier is connected in the focus control and has an offset voltage. An offset compensation voltage is supplied to the input of the control amplifier for compensating the offset voltage of that amplifier. The offset compensation voltage is varied at the input of the control amplifier until the phase relation of the focusing error signal coincides with the phase relation of the data signal for obtaining the correct value for the offset compensation voltage.

Claims

1. An arrangement for reproducing data readable by an optical scanner from tracks on a recorded medium, comprising:

focus control means for focusing at least one beam of light on the medium tracking control means for positioning said beam of light along said tracks;

a photodetector for receiving said beam after being reflected by said medium;

said photodetector generating an electrical data signal with a phase relation, a focusing error signal with a phase relation for indicating the current state of said focus control means, and a tracking error signal indicating the current state of said tracking control means;

control amplifier means in said focus control means and having an offset voltage and an input;

a source of offset compensation voltage connected to said input of said control amplifier for compensating said offset voltage of said control amplifier; and

means for varying said offset compensation voltage at said input of said control amplifier until the phase relation of said focusing error signal coincides with the phase relation of said data signal for obtaining a correct value for said offset compensation voltage, said offset compensation voltage having a correct value when the two phase relations coincide.

2. An arrangement for reproducing data readable by an optical scanner from tracks on a recorded medium, comprising:

focus control means for focusing at least one beam of light on the medium;

tracking control means for positioning said beam of light along said tracks;

a photodetector for receiving said beam after being reflected by said medium;

said photodetector generating an electrical data signal with a phase relation, a focusing error signal with a phase relation for indicating the current state of said focus control means, and a tracking error signal indicating the current state of said tracking control means;

control amplifier means in said focus control means and having an offset voltage and an input;

a source of offset compensation voltage connected to said input of said control amplifier for compensating said offset voltage of said control amplifier; and

means for varying said offset compensation voltage at said input of said control amplifier until the phase relation of said focusing error signal coincides with the phase relation of said data signal for obtaining a correct value for said offset compensation voltage, said offset compensation voltage having a correct value when the two phase relations coincide;

phase comparator means having a first input receiving said data signal, said phase comparator means having a second input receiving said focusing error signal, said phase comparator means having an output;

a microprocessor having an input connected to said output of said phase comparator means said microprocessor having an output;

a digital-to-analog converter with input connected to said output of said microprocessor, said digital-to-analog converter having an output connected to an input of said control amplifier;

said output of said microprocessor having a digital value varying until said phase comparator means emits a signal to said input of said microprocessor indicating that said data signal is in shape with said focusing error signal.

3. An arrangement as defined in claim 2 including analog switch having an input connected to said output of said photodetector, said analog switch having an output variable switch having a control input connected to of said analog switch, said output of said analog switch reacting to a descending edge of a signal;

said switch having an output reacting to an ascending signal;

a second variable switch having a control input connected to said output of said first variable switch said first and second variable switches having a first contact connected to said output of said control amplifier;

additional amplifier having a non-inverting input connected to a second contact of said first variable switch;

a source of reference potential;

capacitor means connected between said source of reference potential and said non-inverting input of said additional amplifier;

said second variable switch having a second contact, said additional amplifier having an inverting input connected to said second contact of said second variable switch;

additional capacitor means connected between said source of reference potential and said inverting input of said additional amplifier;

said additional amplifier having an output connected to said input of said microprocessor.