Abstract:
A phase-locked loop (PLL) device is disclosed. The PLL device includes an interpolator receiving and processing an input signal by an interpolation operation in response to an interpolation timing value to obtain an output signal, a timing error detector in communication with the interpolator for detecting a timing error value of the output signal, a loop filter in communication with the timing error detector for outputting the interpolation timing value to the interpolator in response to the timing error value, and a lock controller in communication with the loop filter for adjusting the interpolation timing value according to a timing quality of the output signal, and providing the adjusted interpolation timing value for the interpolator. A signal generation method for use in the data pick-up device with the aid of the digital phase-locked loop (PLL) device is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a digital phase-locked loop (PLL) device, and more particularly to a digital phase-locked loop (PLL) device for use in a data pick-up device. The present invention also relates to a method for generating a signal for use in the data pick-up device with the aid of the digital phase-locked loop (PLL) device. 
     BACKGROUND OF THE INVENTION 
     Please refer to  FIG. 1A  which is a partial functional block diagram illustrating a conventional data pick-up device, e.g. an optical-disk pick-up device. An analog voltage signal from a pick-up head (PUH) is converted into an asynchronous sampled signal by an analog-to-digital converter (ADC)  11 . Subsequently, the asynchronous sampled signal is adjusted by an all-digital phase-locked loop (PLL) device  12  to output a synchronous sampled signal. The all-digital PLL device  12  includes an interpolator  121 , a timing error detector  122  and a loop filter  123 . The interpolator  121  receives and processes the asynchronous sampled signal to output the synchronous sampled signal. The timing error detector  122  detects a timing error value between the synchronous sampled signal and an expected synchronous sampled signal as shown in  FIG. 1B . The loop filter  123  outputs an interpolation timing value to the interpolator  121  in response to the change of the timing error value. The interpolator  121  proceeds adjustment according to the interpolation timing value for obtaining a better synchronous sampled signal. 
     When the analog voltage signal from the pick-up head involves therein significant noise resulting from unexpected factors such as scratch on the disk face, the timing of the asynchronous sampled signal generated from the analog-to-digital converter  11  is extremely unstable. Therefore, it will take a long time for the all-digital PLL  12  to recover the normal condition after the unexpected factors are removed. Thus, the data pick-up performance of the data pick-up device is adversely affected. 
     Therefore, the purpose of the present invention is to develop a digital phase-locked loop (PLL) device for use in a data pick-up device and a method for generating a stable signal to deal with the above situations encountered in the prior art. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a digital phase-locked loop (PLL) device and a signal generation method for use in a data pick-up device with the digital phase-locked loop (PLL) device, which involve in reduced converging time after the unexpected factors causing the noise are removed. 
     According to an aspect of the present invention, there is provided a phase-locked loop (PLL) device. The PLL device includes an interpolator receiving and processing an input signal by an interpolation operation in response to an interpolation timing value to obtain an output signal, a timing error detector in communication with the interpolator for detecting a timing error value of the output signal, a loop filter in communication with the timing error detector for outputting the interpolation timing value to the interpolator in response to the timing error value, and a lock controller in communication with the loop filter for adjusting the interpolation timing value according to a timing quality of the output signal, and providing the adjusted interpolation timing value for the interpolator. 
     In an embodiment, the lock controller includes a lock detector in communication with the loop filter for outputting a restore signal when the timing quality is in a bad condition, and outputting a backup signal when the timing quality is in a good condition, a register electrically connected to an output end of the loop filter for storing a backup copy of the interpolation timing value, and a multiplexer set electrically connected between the register and the loop filter for allowing the backup copy of the interpolation timing value in the register to be updated in response to the backup signal, and allowing the backup copy of the interpolation timing value to be read by the loop filter in response to the restore signal. 
     In an embodiment, the lock detector includes a timing quality test device comparing a ratio of absolute values of two immediately adjacent output signals respectively leading and following a zero crossing point with a threshold value, and optionally outputting one of an up-counting signal and a down-counting signal according to the comparing result, an up/down counter proceeding an up-counting operation in response to the up-counting signal and a down-counting operation in response to the down-counting signal to produce a counting value, and a comparator set electrically connected to the up/down counter, comparing the counting value of the up/down counter with a backup threshold value and a restore threshold value, outputting the backup signal in response to a first comparison result indicating the counting value crosses the backup threshold value, and outputting the restore signal in response to a second comparison result indicating the counting value crosses the restore threshold value. 
     For example, the input signal is provided by an analog-to-digital converter, and obtained by a sampling operation on an analog voltage signal. In this case, the input signal is an asynchronous sampled signal and the output signal is a synchronous sampled signal. 
     In another embodiment, the lock detector includes a timing quality test device comparing a ratio of absolute values of two immediately adjacent output signals respectively leading and following a zero crossing point with a threshold value, and optionally outputting one of an up-counting signal and a down-counting signal according to the comparing result, an up/down counter proceeding an up-counting operation in response to the up-counting signal and a down-counting operation in response to the down-counting signal to produce a counting value, and a comparator set electrically connected to the up/down counter, comparing the counting value of the up/down counter with a backup threshold value and a restore threshold value, outputting the backup signal in response to a first comparison result indicating the counting value crosses the backup threshold value, and outputting the restore signal in response to a second comparison result indicating the counting value crosses the restore threshold value. 
     According to another aspect of the present invention, a phase-locked loop (PLL) device includes an interpolator receiving and processing an input signal by an interpolation operation in response to an interpolation timing value to obtain an output signal; a timing error detector in communication with said interpolator for detecting a timing error value of said output signal; a lock detector for determining a timing quality of said output signal; and a loop filter in communication with said timing error detector and said lock detector for outputting said interpolation timing value to said interpolator according to said timing error value and said timing quality. 
     According to another aspect of the present invention, there is provided a signal generation method. The method includes steps of detecting a timing error value associated with an input signal, adjusting an interpolation timing value according to the timing error value, proceeding a frequency backup operation to store the adjusted interpolation timing value when the input signal is in a first quality condition, and proceeding the interpolation operation on the input signal according to the stored interpolation timing value to obtain an output signal when the input signal is in a second quality condition. 
     Preferably, the signal generation method further includes a step of proceeding the interpolation operation on the input signal according to the last adjusted interpolation timing value to obtain the output signal when the input signal is in the first quality condition. 
     Preferably, the method further includes steps of detecting the input signal processed by the interpolation operation to determine a quality condition of the input signal, generating a backup signal when the quality condition is the first quality condition, and generating a restore signal when the quality condition is the second quality condition. 
     Preferably, the quality condition is determined by comparing a ratio of absolute values of two immediately adjacent output signals respectively leading and following a zero crossing point with a threshold value. The first quality condition is determined when the absolute values are close to each other to an extent. 
     In an embodiment, the method further includes steps of outputting one of an up-counting signal and a down-counting signal to obtain a count value according to a comparing result of a ratio of absolute values of two immediately adjacent output signals at opposite sides of a zero crossing point and a threshold value, outputting the backup signal in response to the cross of the count value over a backup threshold value, and outputting the restore signal in response to the cross of the count value over a restore threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may best be understood through the following description with reference to the accompanying drawings, in which: 
         FIG. 1A  is a partial functional block diagram of a optical-disk pick-up device illustrating a conventional all-digital PLL device; 
         FIG. 1B  is a schematic diagram illustrating a timing error value between a practical synchronous sampled signal and an expected synchronous sampled signal; 
         FIG. 2  is a functional block diagram illustrating a preferred embodiment of an all-digital phase-locked loop (PLL) device for use in an optical-disk pick-up device according to the present invention; 
         FIG. 3  is a functional block diagram illustrating a preferred embodiment of a loop filter and a lock controller of the all-digital phase-locked loop (PLL) device in  FIG. 2 ; 
         FIG. 4  is a functional block diagram illustrating a preferred embodiment of the lock detector of  FIG. 3 ; 
         FIGS. 5A–5B  are schematic waveform diagrams illustrating synchronous sampled signals in a good timing quality and a bad timing quality, respectively; 
         FIG. 6A  is a functional block diagram illustrating another preferred embodiment of an all-digital phase-locked loop (PLL) device for use in an optical-disk pick-up device according to the present invention; and 
         FIG. 6B  is a functional block diagram illustrating a preferred embodiment of a modified loop filter and a lock detector of the all-digital PLL device in  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
       FIG. 2  schematically illustrates a preferred embodiment of an all-digital phase-locked loop (PLL) device for use in an optical-disk pick-up device according to the present invention. The all-digital PLL device includes an interpolator  21 , a timing error detector  22 , a loop filter  23  and a lock controller  24 . The interpolator  21  receives and processes an asynchronous sampled signal in response to an interpolation timing value to output a synchronous sampled signal. The timing error detector  22  electrically connected the interpolator  21  detects a timing error value between the synchronous sampled signal and an expected synchronous sampled signal. The loop filter  23  electrically connected to the timing error detector  22  outputs an updated interpolation timing value to the interpolator  21  as a reference according to the timing error value. The lock controller  24  is electrically connected between the interpolator  21  and the loop filter  23  and electrically parallel to the timing error detector  22 . The lock controller  24  adjusts the interpolation timing value outputted from the loop filter  23  according to a timing quality of the synchronous sampled signal outputted from the interpolator  21  (detailed descriptions are given later). When the timing quality is in a bad condition, the loop filter  23  keeps outputting a backup copy of the interpolation timing value to the interpolator  21  as a reference. 
     Please refer to  FIG. 3  which is a functional block diagram illustrating a preferred embodiment of a lock controller to cooperate with a loop filter according to the present invention. As shown in  FIG. 3 , the lock controller  24  includes a lock detector  241 , a register  242  and a multiplexer set comprising two multiplexer  2431  and  2432 , and the loop filter  23  includes a phase register  40  and a frequency register  41 . The register  242  is electrically connected to an output end of the loop filter  23  coming across the multiplexer  2431  for storing a backup copy of the interpolation timing value. The lock detector  241  that comes across the multiplexer  2432  to electrically connect to the loop filter  23  outputs a restore signal or a backup signal according to the timing quality of the synchronous sampled signal. When the timing quality is in a good condition, the lock detector  241  outputs the backup signal. The multiplexer  2431  allows a frequency-related counting value of the interpolation timing value stored in the frequency register  41  of the loop filter  23  to be stored into the register  242  to update the backup copy of the interpolation timing value in response to the backup signal. On the other hand, when the timing quality is in a bad condition, the lock detector  241  outputs the restore signal. The multiplexer  2432  allows the backup copy of the interpolation timing value stored in the register  242  to be outputted by the loop filter  23  in response to the restore signal. 
     Please refer to  FIG. 4  which is a functional block diagram illustrating a preferred embodiment of the lock detector of  FIG. 3 . The lock detector  241  includes a timing quality test device  2411 , an up/down counter  2412  and a comparator set  2413 . The timing quality test device  2411  compares a ratio of absolute values of two immediately adjacent synchronous sampled signals respectively leading and following a zero crossing point, which will be described later with reference to  FIGS. 5A and 5B , with a threshold value. The timing quality test device  2411  outputs either an up-counting signal or a down-counting signal to the up/down counter  2412  electrically connected thereto according to the comparing result. The up/down counter  2412  proceeds an up-counting operation in response to the up-counting signal and a down-counting operation in response to the down-counting signal so as to realize a counting value. Subsequently, the comparator set  2413  electrically connected to the up/down counter  2412  compares the counting value with a backup threshold value and a restore threshold value and optionally outputs the backup signal or the restore signal according to the comparing result. When the counting value is greater than the backup threshold value, the backup signal is in logic. 1; otherwise, the backup signal is in logic 0. When the backup signal is in logic 1, it represents that the timing quality is in a good condition, so the multiplexer  2431  of  FIG. 3  allows the frequency in the register  242  to be updated. On the contrary, when the backup signal is in logic 0, it represents that the timing quality is deteriorated to some extent, and the timing error value obtained in this defect region will be far beyond the expected one. Therefore, the backup operation of the interpolation timing value from the frequency register  41  to the register  242  should be suspended. On the other hand, when the counting value is greater than the restore threshold value, the restore signal is in logic 0; otherwise, the restore signal is in logic 1. When the restore signal is in logic 0, representing the timing quality is in the good condition, the frequency obtained from the loop filter  23  is suitable to be directly used for next interpolation operation. On the contrary, when the restore signal is in logic 1, representing the timing quality is in the bad condition, the current frequency is not suitable to be used, so the backup copy of the frequency stored in the register  242  is used for next interpolation operation. Since the backup copy of the frequency is made when the signal quality is still good, the frequency used for the following interpolation operations would not far away from the normal frequency after the abnormal factor is removed. 
     Please refer to  FIGS. 5A and 5B  which show how the timing quality is determined. It is understood that if timing quality is perfect, all the synchronous sampled signals should lie at predetermined levels. Generally, the synchronous sampled signals should be at well symmetric levels. Therefore, two immediately adjacent synchronous sampled signals at opposite sides of the zero crossing point should also be symmetric to each other. Accordingly, by comparing two immediately adjacent synchronous sampled signals at opposite sides of the zero crossing point, the timing quality can be determined. For synchronous sampled signals shown in  FIG. 5A , the ratio of absolute values of two immediately adjacent synchronous sampled signals  51  and  52  at opposite sides of the zero crossing point  50  is very close to the ideal value “1”. In other words, the synchronous sampled signals are well symmetric. Therefore, the timing quality is determined by the timing quality test device  2411  to be good, and the up-counting signal is outputted to counting accumulatively, as mentioned above. Once the ratio of absolute values of two immediately adjacent synchronous sampled signals  53  and  54  at opposite sides of the zero crossing point  50  is far away from the ideal value “1” as shown in  FIG. 5B , the synchronous sampled signals are poorly symmetric. Accordingly, the timing quality test device  2411  will determine the timing quality is in the bad condition and output the down-counting signal to the up/down counter  2412 , as mentioned above. 
     Please refer to  FIG. 6A  which is a functional block diagram illustrating another preferred embodiment of an all-digital phase-locked loop (PLL) device for use in an optical-disk pick-up device according to the present invention. The function and structure of the interpolation  21  and the timing error detector  22  in  FIG. 6A  are similar to those in  FIG. 2 , but a modified loop filter  61  is used instead of the loop filter  23 . As shown in  FIG. 6B , the modified loop filter  61  includes a phase register  611 , a frequency register  612 , a register  613  and two multiplexers  614  and  615 . The modified loop filter  61  cooperates with a lock detector  62  to achieve the functions of the loop filter  23  and the lock controller  24 . 
     As shown in  FIG. 6B , the register  613  stores therein a backup copy of the interpolation timing value. The lock detector  62  outputs a restore signal or a backup signal according to the timing quality of the synchronous sampled signal. When the timing quality is in a good condition, the lock detector  62  outputs the backup signal. The multiplexer  614  allows a frequency-related counting value of the interpolation timing value stored in the frequency register  612  to be stored into the register  613  to update the backup copy of the interpolation timing value in response to the backup signal. On the other hand, when the timing quality is in a bad condition, the lock detector  62  outputs the restore signal. The multiplexer  615  allows the backup copy of the interpolation timing value stored in the register  613  to be outputted in response to the restore signal. The function of the lock detector  62  is similar to the lock detector  241  in  FIG. 3 , and includes a timing quality test device, an up/down counter and a comparator set, similar to those shown in  FIG. 4 . The timing quality test device compares a ratio of absolute values of two immediately adjacent synchronous sampled signals respectively leading and following a zero crossing point with a threshold value. The timing quality test device outputs either an up-counting signal or a down-counting signal to the up/down counter electrically connected thereto according to the comparing result. The up/down counter proceeds an up-counting operation in response to the up-counting signal and a down-counting operation in response to the down-counting signal so as to realize a counting value. Subsequently, the comparator set compares the counting value with a backup threshold value and a restore threshold value and optionally outputs the backup signal or the restore signal according to the comparing result. When the counting value is greater than the backup threshold value, the backup signal is in logic 1; otherwise, the backup signal is in logic 0. When the backup signal is in logic 1, it represents that the timing quality is in a good condition, so the multiplexer  614  of  FIG. 6B  allows the frequency in the register  613  to be updated. On the contrary, when the backup signal is in logic 0, it represents that the timing quality is deteriorated to some extent, and the timing error value obtained in this defect region will be far beyond the expected one. Therefore, the backup operation of the interpolation timing value from the frequency register  612  to the register  613  should be suspended. On the other hand, when the counting value is greater than the restore threshold value, the restore signal is in logic 0; otherwise, the restore signal is in logic 1. When the restore signal is in logic 0, representing the timing quality is in the good condition, the frequency obtained from the modified loop filter  61  is suitable to be directly used for next interpolation operation. On the contrary, when the restore signal is in logic 1, representing the timing quality is in the bad condition, the current frequency is not suitable to be used, so the backup copy of the frequency stored in the register  613  is used for next interpolation operation. Since the backup copy of the frequency is made when the signal quality is still good, the frequency used for the following interpolation operations would not far away from the normal frequency after the abnormal factor is removed. 
     From the above description, when the analog voltage signal from the pick-up head involves therein significant noise resulting from unexpected factors such as scratch on the disk face, the all-digital PLL device according to the present invention can quickly restore the backup copy of the interpolation timing value obtained in the good condition for next interpolation operation so as to efficiently reduce the recovering time after the unexpected factors are removed. Further, the data pick-up performance of the data pick-up device can be improved. Moreover, the disclosed digital phase-locked loop (PLL) device can be established into any device for reading data from a storage medium. For example, any optical reproducing device used to reproduce information from a disc can employ the embodiment for reading data. The optical reproducing device can be a compact disk-read only memory (CD-ROM) drive, a digital versatile disk-read only memory (DVD-ROM) drive, a compact disk-rewritable (CD-RW) drive, a digital versatile disk-recordable (DVD-R) drive, a digital versatile disk-rewritable (DVD-RW) drive, or even a digital versatile disk-random access memory (DVD-RAM) drive. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.