US 5,629,914 A · Data-transition threshold following in optical recording

Abstract

In a pulse width modulated read signal channel for an optical disk drive, a data-transition threshold is maintained for data detection by a threshold tracking circuit that estimates the amplitude centerline data-transition threshold from the most recent maximum and minimum values of the read signal waveform. To improve the accuracy of the response of the centerline estimator, the threshold is increased or decreased based on the phase error at each read signal transition through the data-transition threshold. In addition, defects in the optical recording media are detected, and a defect present signal is used to inhibit the transition phase error input to the centerline estimator. This prevents the estimator from moving the threshold to an incorrect stable level. In addition, the defect present signal boosts the error feedback in the centerline estimator. The estimator then more quickly follows the read signal waveform. As a result, the estimator reacquires the centerline of the waveform after the read head moves past the defect without retriggering the defect detection circuit.

Claims13

Dependent claims

Apparatus for tracking a data detection threshold to an amplitude centerline of a read signal fluctuating between maximum and minimum peaks, said apparatus comprising:

means for estimating the centerline of the read signal in response to a present amplitude mid-point of the read signal and in response to phase errors in transitions of the read signal between minimum and maximum values, said estimating means providing a centerline estimated value as a data detection threshold value;
means for detecting departure of the data detection threshold value from an average centerline value of the read signal and producing a defect present signal as long as the departure is greater than a predetermined amount;
means responsive to said defect present signal for inhibiting the response by said estimating means to phase errors so that the phase errors in transitions of the read signal have no effect on the centerline estimated value;
and
means responsive to said defect present signal for enhancing the response of said estimating means to the present amplitude mid-point so that the centerline estimated value follows the present amplitude mid-point.

2 more elements

Apparatus for tracking a data-detection threshold to a centerline value of a read signal fluctuating between variable maximum and minimum values, said apparatus comprising:

an estimating circuit estimating the centerline value of a read signal based on a present amplitude of the read signal and based on a transition phase error in transitions of the read signal between minimum and maximum values, said estimating circuit providing a centerline estimated value as a data detection threshold value and having an averaging circuit, a difference circuit and a combining circuit to update data detecting threshold value;
said averaging circuit averaging a most recent maximum value with a most recent minimum value to produce a present amplitude mid-point value;
said difference circuit taking the difference between the present amplitude mid-point value and the data-detection threshold value and providing an amplitude mid-point error value;
said combining circuit updating the data-detection threshold value with the amplitude mid-point error value and a transition phase error value from a most recent data-transition;
a defect detector circuit detecting departure of an average centerline value of the read signal from the data detection threshold value and producing a defect present signal as long as the departure is greater than a predetermined amount;
gating circuits, responsive to said defect present signal, inhibiting the transition phase error value from reaching said combining circuit;
and
a gain circuit, responsive to said defect present signal, boosting the amplitude mid-point error value provided to said combining circuit.

5 more elements

A method for tracking a data-detection threshold to a centerline value of a read signal from a pulse width modulated recording fluctuating between variable maximum and minimum values, said method comprising the steps of:

averaging a most recent maximum value of the read signal with a most recent minimum value of the read signal to produce a present amplitude mid-point value;
summing the difference between the present amplitude mid-point value and the data-detection threshold value and providing an amplitude mid-point error value;
updating the data-detection threshold value with the amplitude mid-point error value and a transition phase error value from a most recent data-transition to produce an updated data-detection threshold value;
detecting departure of an average centerline value of the read signal from the data-detection threshold value and producing a defect present signal as long as the departure is greater than a predetermined amount;
inhibiting said updating step from updating the data-transition threshold with the transition phase error during the duration of the defect present signal;
and
boosting the amplitude mid-point error value used in the updating step during the duration of the defect present signal.

4 more elements

Dependencies are inferred from the claim text.

Data-transition threshold following in optical recording

Life of this patent

Data-transition threshold following in optical recording

Life of this patent

Abstract

Claims13