Digital partial response asymmetry compensation
View Patent ↗A method is provided for receiving and restoring data from an optical recording medium exhibiting strong asymmetry in the regenerated RF signal. The method provides digital partial response asymmetry compensation of a digital RF signal. The asymmetry of the digital RF signal is detected through the measurement of the envelopes of a short T pulse (xT pulse) and a long T pulse (yT pulse), where the T is the bit clock of the recovered bit stream. Through the evaluation of the xT upper and lower envelopes and the asymmetry factor, upper and lower thresholds are determined. Only the asymmetric parts of the digital RF signal are selected and compensated.
1. A method for digital partial response asymmetry compensation of a digital data signal, the method comprising:
providing pulses of the digital data signal having a pulse length equal to or smaller than a first value to a first signal path and providing pulses of the digital data signal having a pulse length equal to or greater than a second value to a second signal path, the second value being larger than the first value;
determining an asymmetry value of the digital data signal by measuring envelopes of the pulses in the first signal path and measuring envelopes of the pulses in the second signal path;
determining upper and lower thresholds by evaluating upper and lower envelopes of the pulses in the first signal path and the asymmetry value; and
selecting and compensating only asymmetric parts of the digital data signal using the determined upper and lower thresholds.
2. The method according to claim 1 , comprising filtering a DC-component in the digital data signal to generate a DC-free digital data signal.
3. The method according to claim 1 , further comprising separating pulses having a pulse length equal to or smaller than the first value and pulses having a pulse length equal to or greater than the second value from the digital data signal, respectively, according to a zero-crossing information in the digital data signal.
4. The method according to claim 3 , further comprising floating the digital data signal with an offset.
5. The method according to claim 1 , wherein measuring the envelopes of the pulses in the first signal path and the pulses in the second signal path comprises:
detecting a maximum value and a minimum value of each pulse;
filtering all detected maximum values and minimum values by a low-pass filter.
6. The method according to claim 1 , further comprising determining the asymmetry value from a look-up table.
7. The method according to claim 1 , further comprising indicating a quality of a recording medium from which the digital data signal is obtained based on the determined asymmetry value.
8. The method according to claim 1 , further comprising optimizing subsequent processing blocks using the determined asymmetry value.
9. The method according to claim 1 , further comprising performing an analog automatic gain control or a digital automatic gain control using the measured upper and lower envelopes of the pulses in the second signal path.
10. An apparatus for retrieving a digital data signal from a recording medium, wherein said apparatus comprises:
a first pulse separator configured to provide pulses of the digital data signal having a pulse length equal to or smaller than a first value to a first signal path;
a second pulse separator configured to provide pulses of the digital data signal having a pulse length equal to or greater than a second value to a second signal path, the second value being larger than the first value;
an asymmetry detector configured to determine an asymmetry value of the digital data signal by measuring envelopes of the pulses in the first signal path and measuring envelopes of the pulses in the second signal path;
a threshold determination block configured to determine upper and lower thresholds by evaluating upper and lower envelopes of the pulses in the first signal path and the asymmetry value; and
an asymmetry compensation block configured to select and compensate only asymmetric parts of the digital data signal using the determined upper and lower thresholds.
11. The apparatus according to claim 10 , further comprising an AC-coupling block configured to filter a DC-component in the digital data signal to generate a DC-free digital data signal.
12. The apparatus according to claim 10 , wherein the first pulse separator and the second pulse separator are configured to separate the pulses from the digital data signal according to a zero-crossing information in the digital data signal.
13. The apparatus according to claim 12 , further comprising an adder configured to float the digital data signal with an offset.
14. The apparatus according to claim 10 , wherein for measuring the envelopes of the pulses in the first signal path and for measuring the envelopes of the pulses in the second signal path the apparatus further comprises:
upper envelope measurement blocks and lower envelope measurement blocks configured to detect a maximum value and a minimum value of each pulse, and
a low-pass filter configured to filter all detected maximum values and minimum values.
15. The apparatus according to claim 10 , wherein the asymmetry detector is configured to determine the asymmetry value from a look-up table.
16. The apparatus according to claim 10 , further comprising a microprocessor configured to use the determined asymmetry value as an indication of a quality of a recording medium from which the digital data signal is obtained.
17. The apparatus according to claim 10 , wherein the apparatus is configured to optimize subsequent processing blocks using the determined asymmetry value.
18. The apparatus according to claim 10 , wherein the apparatus is configured to perform an analog automatic gain control or a digital automatic gain control using the measured upper and lower envelopes of the pulses in the second signal path.