Duty ratio control apparatus for pre-pit detection or header detection of an optical storage medium

A detecting device for detecting a header region of an optical storage medium, the detecting device comprising:

• a first slicer for generating a first sliced signal corresponding to a push-pull signal and a first reference level, wherein the push-pull signal is retrieved from the optical storage medium;
• a first duty ratio controller coupled to receive the first sliced signal for adjusting the first reference level or the push-pull signal to control a duty ratio of the first sliced signal to a first predetermined ratio;
• a first reference level generator coupled to the first duty ratio controller for generating a second reference level corresponding to the first reference level;
• a second slicer coupled for generating a second sliced signal corresponding to the push-pull signal and a third reference level;
• a second duty ratio controller coupled to receive the second sliced signal for adjusting the third reference level or the push-pull signal to control a duty ratio of the second sliced signal to a second predetermined ratio greater than the first predetermined ratio;
• a second reference level generator coupled to the second duty ratio controller for generating a fourth reference level corresponding to the third reference level;
• and
• a header region detecting module coupled to receive the second reference level, the fourth reference level, and the push-pull signal for detecting a header region of the push-pull signal according to the second and fourth reference levels.

A detecting device for detecting a header region of an optical storage medium, the detecting device comprising:

• a slicer for generating a sliced signal corresponding to a received push-pull signal retrieved from the optical storage medium and a first reference level;
• a duty ratio controller coupled to receive the sliced signal for adjusting the first reference level or the push-pull signal to control a duty ratio of the sliced signal to a predetermined ratio;
• a reference level generator coupled to receive the first reference level output from the duty ratio controller for generating a second reference level corresponding to the first reference level;
• and
• a header region detecting module coupled to receive the second reference level, the push-pull signal, and a third reference level for detecting a header region of the push-pull signal according to the second reference level and the third reference level, the third reference level corresponding to the second reference level.

A duty ratio control loop comprising:

• a slicer for slicing an incoming signal and a reference level to generate a sliced signal;
• and
• a duty ratio controller coupled to receive the sliced signal for adjusting the reference level or the incoming signal to control a duty ratio of the sliced signal to a predetermined ratio, the duty ratio controller comprising:
• a duty detector coupled to the slicer for detecting the duty ratio of the sliced signal;
• and
• an adjusting device coupled to the duty detector and the slicer for adjusting the reference level or the incoming signal according to the detecting result of the duty detector, the adjusting device comprising:
• a decision unit coupled to the duty detector for generating a control value according to the detecting result of the duty detector;
• a gain amplifier coupled to the slicer;
• and
• a digital-to-analog converter (DAC), coupled to and disposed between the decision unit and the gain amplifier, for controlling the gain amplifier to adjust the gain of the incoming signal according to the control value;
• wherein the adjusting device adjusts the gain of the incoming signal according to the detecting result of the duty detector.