DVD−R/RW and DVD+R/RW recorders
View Patent ↗A method and apparatus for recording data at specific locations on a DVD includes selectively detecting the occurrence of wobble sync during a window computed from previous occurrences of wobble sync and eight-to-fourteen modulation sync. The method and apparatus also uses a phase-locked loop to recover the wobble signal, including wobble sync, and computes phase drift between wobble sync and eight-to-fourteen modulation sync and applies a compensation profile, compatible with a read clock phase-locked loop, to the wobble phase-locked loop.
1. A method of operating a digital versatile disk (DVD) reader/recorder including a wobble channel carrying wobble channel symbols recovered from a DVD and a data channel carrying data channel sync patterns recovered from the DVD in a DVD recorder, comprising:
deriving a write clock from the recovered wobble channel symbols;
monitoring time-varying time intervals from when the data channel sync patterns carried in the data channel are recovered to when the wobble channel symbols carried in the wobble channel are recovered;
computing a window of time during which a next wobble symbol is expected;
computing a phase drift between data channel sync patterns and wobble channel symbols based on the monitored time-varying time differences;
adjusting the computed window by the phase drift computed;
searching for the next wobble symbol during the adjusted, computed window;
adjusting the derived write clock to compensate for the phase drift computed;
tracking wobble channel signal phase with a wobble phase locked loop (PLL) having a control signal derived from the wobble channel input phase and operating as a closed loop independent of the data channel; and
overriding closed loop operation of the PLL by modifying the control signal of the PLL from its derivation from the wobble channel signal phase to perform the adjusting to compensate for the phase drift.
2. The method of claim 1 , wherein adjusting is performed substantially continuously.
3. The method of claim 1 , further comprising:
adding to the closed loop during overriding a compensation signal derived externally to the closed loop to compensate for the phase drift.
4. A method of operating a digital versatile disk (DVD) recorder to record on a DVD medium including a wobble channel and a data channel, comprising:
recovering wobble channel symbols from the DVD medium using a wobble PLL having a control signal representative of a wobble channel symbol phase;
recovering data channel sync patterns from the DVD medium;
monitoring time-varying time intervals from when the data channel sync patterns are recovered to when the wobble channel symbols are recovered;
computing a window of time during which a next wobble symbol is expected;
computing a phase drift between data channel sync patterns and wobble channel symbols based on the monitored time-varying time differences;
adjusting the computed window by the phase drift computed;
searching for the next wobble symbol during the adjusted, computed window;
deriving from the computed phase drift a time-varying compensation profile independent of the wobble channel symbol phase applied to the control signal of the wobble PLL,
tracking wobble channel signal phase with a wobble phase locked loop (PLL) having a control signal derived from the wobble channel input phase and operating as a closed loop independent of the data channel; and
overriding closed loop operation of the PLL by modifying the control signal of the PLL from its derivation from the wobble channel signal phase to perform the adjusting to compensate for the phase drift.
5. The method of claim 4 , further comprising:
writing user write data using a write clock derived from the wobble PLL;
recovering user written data from the DVD medium using a read data PLL; and
deriving further comprises constructing the time-varying compensation profile such that when applied, the wobble PLL keeps phase differences between the user write data and the user written data within a range recoverable by the read data PLL.
6. A method of operating a digital versatile disk (DVD) reader/recorder to record on a DVD medium including a wobble channel and a data channel, comprising:
recovering wobble channel symbols having a known spacing from the DVD medium using a wobble PLL;
recovering data channel sync patterns from the DVD medium;
generating data channel sync patterns for writing to the DVD medium;
monitoring time-varying time intervals from when the data channel sync patterns are recovered to when the wobble channel symbols are recovered;
computing a window of time during which a next wobble symbol is expected;
determining a phase drift between the data channel sync patterns and the wobble channel symbols based on the monitored time-varying time differences;
adjusting the computed window by the phase drift determined;
searching for the next wobble symbol during the adjusted, computed window; and
writing data to the DVD medium at times derived from the wobble channel symbols as adjusted based upon the determined phase drift;
tracking wobble channel signal phase with a wobble phase locked loop (PLL) having a control signal derived from the wobble channel input phase and operating as a closed loop independent of the data channel; and
overriding closed loop operation of the PLL by modifying the control signal of the PLL from its derivation from the wobble channel signal phase to perform the adjusting to compensate for the phase drift.
7. The method of claim 6 , further comprising:
determining where to write data to the DVD medium by combining the determined phase drift and a location at which a recent data channel sync pattern has been generated.