Abstract:
An automatic detecting device of land pre-pits signal is disclosed. The device adjusts gain of push-pull signals to raise the signal to noise ratio of the land pre-pits signal to the wobble signal. Digital logic computation is also utilized to recognize the practical position of the land pre-pits. The level automatic detection of the RC circuit and the fixed slice level compose an automatic slice level, which is the basis for detecting the land pre-pits. The disclosed device eliminates the drawback of not easy to obtain correct land pre-pits signal from written disks by the conventional of fixed land pre-pits slice level technology.

Description:
This nonprovisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No(s). 092118247 filed in TAIWAN, R.O.C. on Jul. 3, 2003, which is (are) herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to an automatic detecting device for signals of land pre-pits on digital video/audio optical disks, utilizing gain adjustment of push-pull signals to raise the signal to noise ratio of the land pre-pits signal to the wobble signal. Digital logic computation is also utilized to recognize the practical position of the land pre-pits. The level automatic detection of the RC circuit and the fixed slice level compose an automatic slice level, which is the basis for detecting the land pre-pits. 
   2. Related Art 
   A current write-once DVD (DVD-R) or re-writable DVD (DVD-RW) has the same structure, where records relative data, such as laser wavelength, write power, write strategy, manufactures, or track positions.  FIG. 1A  illustrates the schematic diagram of the data tracks of a DVD. The land pre-pits  15  of a DVD-R or a DVD-RW are formed in the grooves  17  relative to the peak of the wobbles. The grooves  11  and the lands  17  interlace with each other. After data are recorded in the grooves  11  of the disk, a mark  12  is written in the pre-pits area  15  of the land  17 , as shown in  FIG. 1B . The un-continuity of the lands  17  in each land pre-pits area  15  results in edge effect of heat diffusion. The mark  12  in the grooves  11  diffuses to the pre-pits area  15 . The LPP signal is thus influenced. The amplitude of LPP signals relative to the wobble signal decreases after data are written onto the disk. This leads to decrease of the signal to noise ratio. 
     FIG. 2A  shows the waveform of land pre-pits (LPP) signals not being affected by written data before writing a DVD. A constant LPP slice level, as denoted by dot lines in the figure, is adopted to obtain correct digital LPP signals through comparators.  FIG. 2B  shows the waveforms after the DVD is written. The LPP signal is usually generated by push-pull approach and constant LPP slice level. The LPP signal is illustrated as waveform A. After data are written on the disk, the amplitude of the LPP signals relative to the wobble signals recesses, which is illustrated as waveform B in the figure. In this situation, adoption of the constant LPP signal slice level brings low accuracy of the LPP signal. The accuracy is still low, even after being protected through Error Correcting Code (ECC). The phenomenon affects access of the lead-in information of the disk drive and access of the address during track jump. The characteristic of the LPP signal of the inner circle and that of the outer circle is not in unanimity during tracking following on the same disk. Furthermore, the influence of written data, the difference between different disks, and writing times lead to accuracy decrease of the LPP signals. Therefore, an automatic level adjusting mechanism is necessary to obtain correct LPP signals under all circumstances. 
     FIG. 3  describes the circuit for generating LPP signals of the prior art. The circuit involves comparing the fixed LPP slice level V 1  and the LPP signal V 2  in the comparator  31  to obtain the LPP slice signal V 12 . The LPP slice signal V 12  is synchronized with the wobble clock V 3  through the noise gate  33  in the circuit to eliminate unnecessary glitches. The filtered LPP slice signal V 4  is delivered to a LPP decoder  35 . Under the influence of high frequency RF signals, the amplitude of LPP signals relative to the wobble signal decrease after data are written onto the disk. Therefore, the credibility of the LPP slice signal before writing data onto the DVD is better than that after writing data onto the DVD. 
     FIG. 4  illustrates the block diagram of the circuit of the prior art for amending the slice level of land pre-pits. The circuit improves the method of the constant slice level of land pre-pits. The land pre-pits signal V 2  is delivered to a level limiter  41  and filtered by a band pass filter  43 , thereby amending the slice level. The filtered signal is then computed with the constant slice level V 1  and the computed signal is then sent to the comparator  31  to compare with the land pre-pits signal V 2 . The land pre-pits signal V 12  is thus obtained. In order to eliminate the unnecessary pulse interference, the land pre-pits signal V 12  is synchronized with the wobble clock V 3  through the noise gate circuit  33 . The protected land pre-pits signal V 4  is then generated and delivered to the land pre-pits decoding circuit  35 . However, the affection of the adjacent land pre-pits causes the insufficient amendment in the slice level and erroneous judgment of land pre-pits. The accuracy rate of the LPP signals is not improved too much. 
   The invention employs automatic detection to detect the variation of the wobble signals to overcome the technical difficulties of prior art, and improves the accuracy rate of the LPP signals in coordination with digital logic computation. 
   SUMMARY OF THE INVENTION 
   The main object of the invention is to provide an automatic detecting device for land pre-pits signals. The LPP auto slice level technology overcomes the heat diffusion affection of the LPP signal on the land when writing data in grooves. The heat diffusion weakens the amplitude of the written LPP signal. Therefore, adopting a constant LPP slice level is not easy to obtain the LPP signal precisely. In order to raise the signal to the noise ratio of the LPP signal and wobble signal, the gain of the push-pull signal is adjusted. The practical position of land pre-pits is recognized by digital logical technology. Judgment of the land pre-pits is based on the automatic slice level, combined with the level automatic detection of the RC circuit and the fixed slice level. The method involves the influence of the written data to the wobble signal such that the possibility of slicing error digital LPP signals is greatly reduced. The drawback of not easily obtainable correct LPP signals from disks with recorded data through the constant LPP slice level technology of prior art is eliminated. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given n the illustration below only, and is thus not limitative of the present invention, and wherein: 
       FIG. 1A  is the schematic diagram of data tracks of a writable DVD of the prior art; 
       FIG. 1B  is the schematic diagram showing writing data; 
       FIG. 2A  is the waveform of the LPP signal of a writable DVD before writing; 
       FIG. 2B  is the waveform of the LPP signal of a writable DVD after writing; 
       FIG. 3  is LPP signal generating circuit of the prior art; 
       FIG. 4  is the circuit for amending LPP slice level; 
       FIG. 5  is the schematic diagram the data tracks of a writable DVD; 
       FIG. 6  is the signal of LPP automatic detection slice level of the invention; and 
       FIG. 7  is the circuit of LPP signal automatic slice level detecting device of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 5  illustrates the data tracks of a writable DVD. The figure shows the relationship of the wobble signals and land pre-pits (LPP). The land pre-pits  55  on the writable DVD are formed on the peak of the wobbles on the lands  57 . The grooves  51  and the lands  57  interlace with each other on the data tracks. The push-pull method is employed to obtain the LPP signals from the lands  57 . The gain of the puhs-pull signals is properly adjusted in order to raise the signal to the noise ratio of the grooves  51  to the wobble signals. 
   The invention discloses two methods to raise the accuracy rate of digital LPP signals.  FIG. 6  describes the signals of the LPP signals automatic detecting the slice level of the embodiment of the invention. In view of digital signal processing, an optical pickup head retrieves a LPP signal, as shown in part A in the figure. In order to obtain the LPP position, a digital logic circuit is used to generate a wobble clock, as shown in part D in the figure. Two adjacent land pre-pits are separated by at least 8 wobble clocks according to the DVD specification. The LPP signal is divided into several portions according to the wobble signal. Each portion has eight wobble clocks. The previous three clocks may include LPP signals, while the latter five wobble signals do not have the LPP signals. A LPP window, as shown in part E in  FIG. 6 , is generated for forecast in accordance to the wobble clock. The LPP window, which is open for three clocks and close for five clocks, is used as switching timing of RC impedance. The previous three clocks are for fast RC charge/discharge processing, while the latter five clocks are for slow RC charge/discharge processing, and a bottom hold signal is then generated accordingly, as shown in part F of  FIG. 6 . A sample and hold signal in part G of  FIG. 6  is used to retrieve the bottom hold signal to obtain the hold level signal as shown in part H of  FIG. 6 . After obtaining the LPP-sliced signal, it needs to be synchronized with the wobble clocks in order to obtain the LPP-protect signal as shown in part C in  FIG. 6 . The correct positions of LPP are consequently obtained, and the unnecessary glitches are eliminated. LPP Error Code Detection and Correction then proceeds to obtain precise LPP information. 
   In view of analog signal processing, the invention utilizes an automatic slice level. The sample and hold signal in  FIG. 6  are used to sample and hold the LPP bottom signal in the area without land pre-pits. The level of the LPP bottom signal is recorded in the capacitor based on the RC charge/discharge principle. The RC circuit with larger resister value is used to sample and hold the LPP bottom signal to obtain a stable bottom signal level. In the area with land pre-pits, the sampled and held bottom signal and a fixed slice level are performed as analog computation to obtain a level-slicing signal. The digital LPP signals are obtained from a comparator processing the obtained level and the LPP signal. To avoid the stable bottom signal level in the RC circuit from being affected by the LPP signal, the resister value in the RC circuit becomes smaller when the LPP window is at high level such that quick change can prevent the bottom signal from being affected by the LPP signal. Therefore, the LPP bottom signal varies severely when the LPP window is at high level. The amplitude variation of the wobble signal caused by adjacent tracks and the influence after data writing can be eliminated through the proper slice level, generated by the LPP signal level automatic detecting device, to prevent the comparator from generating erroneous digital LPP signals and to raise the accurate rate. 
     FIG. 7  illustrates the circuit of the LPP signal level automatic detecting device. The circuit corresponding to the signals in  FIG. 6  is described in details. 
   An optical pickup head  601  of an optical pickup circuit  600  in a writable DVD drive accesses the digital data on the disk. A second signal  62  is delivered to a gain balancer  605  to obtain a fourth signal  64 , whose amplitude is the same as the first signal  61 . A third signal  63  is generated by the first signal  61  and the fourth signal  64  through a push-pull method. The third signal  63  is then transmitted to a spin motor controller  603  through the wobble phase lock loop (PLL)  602 , thereby controlling the spin motor  604  in the drive. The control signal can be implemented by prior art. 
   The fourth signal  64  is delivered to a gain weightier  606  to generate the fifth signal  65  such that the signal to noise ratio of the LPP signal and the wobble signal is raised through adjusting the first signal  61  and the fifth signal  65 . The fifth signal  65  and the first signal  61  are added to obtain the LPP signal A, which is delivered to a comparator  607  and a bottom signal generator  609  respectively. The bottom signal generator  609  produces the LPP bottom signal F, which is shown in  FIG. 6 , through the LPP signal A and the LPP window E from the digital processor  60 . The sample signal generator  610  receives the LPP bottom signal F and the sample signal from the digital processor  60  to obtain a level hold signal H. The level hold signal H and a constant LPP slice signal V 1  generated by a fixed voltage are transmitted to an analog computer  608 , thereby producing the LPP sliced level signal I. 
   The comparator  607  receives the LPP signal A, which is processed by the gain balancer  605  and the gain weightier  606 , and the LPP sliced level signal I. The two signals are compared to obtain the LPP signal B as shown in  FIG. 6 . 
   The bottom signal generator  609  and the sample signal generator  610  receive the LPP window E and the sample signal G from the digital processor  60  to obtain the sliced level signal H. 
   The digital processor  60  includes a synchronous signal corrector  611 , a LPP window generator  612 , and a LPP decoder  613 . The synchronous signal corrector  611  receives the LPP sliced signal B from the comparator  607  and the wobble clock D from the PLL  602  for synchronous correction. The LPP window generator  612  receives the fixed wobble clock generated from PLL  602 , thereby generating a signal that is open for three pulses and closed for five pulses, which signal is shown in  FIG. 6 . The LPP window E and the LPP signal from the synchronous signal corrector  611  are proceeded AND logic computation to generate the protected LPP signal C. The LPP decoder  613  receives the protected LPP signal C for decoding the land pre-pits to obtain the land pre-pits information. 
   The automatic adjusting slice level of the land pre-pits is obtained by the slice level, which is generated by the bottom signal generator  609  and the sample signal generator  610 , through the analog computer  608 . Then the LPP position signal C is obtained through the comparator  607 , the synchronous corrector  611  and the LPP window generator  612 . Finally, the precise LPP information is obtained from the LPP decoder  613 . 
   The LPP signal level automatic detecting device of the invention utilizes a LPP signal level automatic detection technology to detect the variation of the wobble signal, to overcome the drawback of the conventional technology. The accuracy of the LPP signal is improved by digital logic computation, and the unnecessary glitches are eliminates. The error rate of decoding LPP signals due to the LPP signals error reduces substantially. 
   Reading the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.