Abstract:
A method and related circuit for synchronizing a writing clock with a wobble clock of a compact disk (CD) drive. The CD drive is capable of rotating a CD that has a data track for recording data and a wobble track. The CD drive is capable of generating the wobble clock according to movement of the wobble track while the CD is rotating. Also the CD drive is capable of writing data on the data track according to the writing clock. The method includes adjusting the frequency of the writing clock so as to synchronize the writing clock and the wobble clock.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and related devices for synchronizing a wobble clock with a writing clock of a compact disk (CD) drive, and more particularly, to a method and related devices for synchronizing the wobble clock with the writing clock by adjusting the frequency of the writing clock. 
     2. Description of the Prior Art 
     In this modern information based society, one of the major concerns is how to manage and store tremendous amounts of information. Compared to other kinds of storage media, a compact disk has a small size and a higher-density storage capacity. Due to developments in recordable and rewritable compact disk technology, consumers have the ability to utilize compact disk storage capacity on their personal computers. 
     Similar to general compact disks, the recordable compact disk (CDR) also has a plurality of pits and lands arranged along a data track for recording digital data. Furthermore, the recordable compact disk comprises a wobble track positioned adjacent the data track for recording wobble signals, which are used for separating the recordable compact disk into a plurality of areas on the surface of the CD. Each of the areas is defined as a big frame or a mini-frame, and is separated into ninety-eight small subframes, in which each of the small subframes comprises 588 channel bits for recording digital data. Because there is no data stored in the data track of a blank recordable CD, the CD drive cannot distinguish the big frames from each other according to the data track before data are written on the data track. In order to orientate the big frames, the wobble track of the recordable CD records wobble signals. Please refer to  FIG. 1  which is a top view of a recordable compact disk  10 . 
     As shown in  FIG. 1 , the compact disk  10  comprises a reflecting surface  13 . On the reflecting surface  13  of the compact disk  10 , there is a fine spiral track  11 . Please refer to  FIG. 1 , which shows a magnified view  1 A of the fine track  11 . The track  11  is composed of two types of tracks, one being a data track  12  to record data, and the other being a wobble track  14  positioned adjacent to the data track  12 . As illustrated in the magnified view  1 A, the data track  12  has a continuously spiral shape, while the wobble track  14  has an oscillating shape. Additionally, the curvature of the wobble track  14  is composed of small segment curves. In a further magnified view  1 B in  FIG. 1 , an interrupt and discontinuity record mark  16  is shown within data track  12 . The length of each record mark  16  varies, and the reflection index of the record mark  16  is different from that of the reflecting surface  13 . The record mark  16  is used to allow the compact disk drive to be able to write data on the compact disk  10 . The surface of the wobble track  14  protrudes beyond the reflecting surface  13 , and the reflection index of the wobble track  14  is also different from that of the reflecting surface  13 . The data track  12  is located inside a groove formed by the raised wobble track  14  surface as shown in  FIG. 2 , which is a three-dimensional perspective view of the magnified view  1 B of the compact disk  10 . As the compact disk  10  rotates, the compact disk drive detects the variation of the reflection light from the small segment curves of the wobble track  14  so as to generate a wobble signal. The wobble signal is a frequency-modulated signal and represents different digital data through varied frequencies. The compact disk drive generates a harmony signal, which is used for orientating the big frames of the data track  12 , by decoding the wobble signal. 
     In other words, when the compact disk drive writes data on to the recordable compact disk  10 , the CD drive analyzes the distribution of the big frames of the data track  12  by decoding the wobble signal read from the wobble track  14 . Because the CD drive writes data on to the data track  12  while the compact disk rotates, the operations of writing must be synchronized with the rotation of the compact disk. The CD drive, thus, can write the digital data on the correct locations of the data track  12 . Please refer to FIG.  3 .  FIG. 3  is a timing diagram of waveforms of related signals of a CD drive. When digital data is written on the recordable compact disk  10 , the CD drive controls the length of each channel bit according to a writing clock Cw. The length of each period of the writing clock Cw determines the length of corresponding record marks  16 . As previously mentioned, each big frame of the data track  12  is composed of a plurality of channel bits. Therefore, a frame clock Cf, which corresponds to the big frames, can be generated according to the writing clock Cw. One period of the frame clock Cf is defined as the time duration Tfw in which the CD drive writes data on to a corresponding big frame. The waveforms of the writing clock Cw and the frame clock Cf are shown in FIG.  3 . Additionally, the CD drive also can decode the wobble clock Cb 1  and the harmony signal S 1  while the CD is rotating over an optical module of the CD drive. Generally, the harmony signal S 1 , which corresponds to the rotation speed of the CD, should be synchronized with the frame clock Cf that is used to control the operations of the optical module while the CD is being written, as shown in FIG.  3 . In other words, if the optical module operates correctly, the harmony signal S 1 , which has periods Tf for locating the positions of big frames of the CD, must have the same period and frequency as the frame clock Cf, which has periods Tfw, and synchronizes with the writing clock Cw. Moreover, the phase difference between the harmony signal S 1  and the frame clock Cf is equal to zero or is less than a predetermined error range. Therefore, the CD drive is capable of writing data on correct positions according to the harmony signal S 1 , which is associated with the wobble track  14 . 
     However, if the rotation speed of the CD is too fast, the wobble track  14  and the data track  12  rotate over the optical module faster, and this makes the periods of the harmony signal shorten. As shown in  FIG. 3 , another set of wobble signal Cb 2  and harmony signal S 2  correspond to such a condition. Because the frame clock Cf does not synchronize with the harmony signal S 2 , the CD drive may write data on wrong big frames of the CD. Similarly, another set of wobble signal Cb 3  and harmony signal S 3 , shown in  FIG. 3 , correspond to a condition in which the rotation speed of the CD is too slow. The CD drive also writes data on wrong big frames of the CD according to the frame clock Cf, which does not synchronize with the harmony signal S 3 . 
     Each of CD drives must have a control circuit for synchronizing the frame clock with the harmony signal. Please refer to  FIG. 4 , which is a function block diagram of a CD drive  20  having a control circuit  22  according to the prior art. The CD drive  20  is used to write data on the CD  10 , and comprises the control circuit  22 , a motor  34 , and an optical module  32 . The motor  34  rotates the CD  10 . The optical module  32  generates corresponding time-variable signals by detecting the data track  12  and the wobble track  14  while the CD  10  is rotating, and generates a corresponding harmony signal S 0  according to the corresponding time-variable signals. Moreover, the optical module  32  can also write data on the data track  12  according to a writing clock Cw 0 . The control circuit  22  has a synchronization circuit FC, a frequency divider  24 , a phase detector PD 0 , a frequency detector FD 0 , a sub-control circuit  28 , a switch circuit  30 , and an activating circuit  26 . The synchronization circuit FC can generate the writing clock Cw 0  according to a system clock Cs 0  that has fixed time periods, and further comprises a frequency divider and a phase-locking circuit that are used to synchronize the writing clock Cw 0  with the system clock Cs 0 , where the ratio between the periods of the writing clock Cw 0  with the system clock Cs 0  is equal to a constant. Because the system clock Cs 0  has a plurality of periods with the same interval, the periods of the writing clock Cw 0  also correspond to the same time duration. The writing clock Cw 0  is divided by a predetermined ratio D 0  via the frequency divider  24  so as to generate a frame clock Cf 0 . That means that the period of the frame clock Cf 0  is D 0  times of the period of the writing clock Cw 0 . As previously mentioned, there are a plurality of channel bits in a big frame, and one of the periods of the frame clock Cf 0  corresponds to an equivalent number of the periods of the writing clock Cw 0 , so that the ratio D 0  can be determined. The phase detector PD 0  and the frequency detector FD 0  respectively detect the phase difference and the frequency difference between the frame clock Cf 0  and the harmony signal S 0 , and the outputs of the phase detector PD 0  and the frequency detector FD 0  transmit to activating circuit  26  and the sub-control circuit  28 . The sub-control circuit  28  has a low-pass frequency filter to filter the signal received from the phase detector PD 0  and the frequency detector FD 0 . The switch circuit  30  is turned on/off by an input signal Mode so as to determine whether to transmit the output signal of the sub-control circuit  28  to the activating circuit  26 . The activating circuit  26  can transmit a corresponding activating signal M 0  to the motor  34  according to the inputs received from the phase detector PD 0 , the frequency detector FD 0 , and the sub-control circuit  28  so as to control the rotation speed of the CD  10 . 
     The control circuit  22  is used to synchronize the harmony signal S 0  with the frame clock Cf 0  so as to make the optical module  32  write data on the correct position of the CD  10 . According to the prior art, the frame clock Cf 0  is generated according to the system clock Cs 0 , which has periods with the same interval, so the time duration of each period of the frame clock Cf 0  is fixed and the frame clock Cf 0  can be taken as a standard clock signal. Additionally, the harmony signal S 0  generated by the optical module  32  can respond to the rotation speed of the CD  10 . The frame clock Cf 0  and the harmony signal S 0  are transmitted to the phase detector PD 0  and the frequency detector FD 0  to compare their phases and frequencies respectively, and the results of the phase detector PD 0  and the frequency detector FD 0  transmit to the activating circuit  26  so that the activating circuit  26  can control the rotation speed of the motor  34  according to the received results. For example, if the motor  34  rotates too fast, the frequency of the harmony signal S 0  increases, and then the phase detector PD 0  and the frequency detector FD 0  compare the harmony signal S 0  with the frame clock Cf 0  and generate corresponding signal and transmit it to the activating circuit  26  to reduce the rotation speed of the motor  34 . In other words, the method according to the prior art adjusts the phase and the frequency of the harmony signal S 0  so as to synchronize the harmony signal S 0  with the frame clock Cf 0 , which has fixed frequency. 
     To write data on the correct position on the CD  10 , the control circuit  22  should eventually make the phase difference and the frequency difference between the frame clock Cf 0  and the harmony signal S 0  equal to zero. However, the motor  34  cannot be driven, if there is not any signal with a nonzero voltage (or current) transmitted to the motor  34 . When there is not any phase difference or frequency difference between the frame clock Cf 0  and the harmony signal S 0 , the phase detector PD 0  and the frequency detector FD 0  do not transmit any signal to the activating circuit  26 . To avoid shutting down the motor  34  when the CD drive  20  writes data on the CD  10  and the phase difference and the frequency difference between the frame clock Cf 0  and the harmony signal S 0  are equal to zero, a sub-control circuit  28  is needed to transmit signals to the activating circuit  26  in a timely manner. Therefore, the method according to the prior art comprises the two following steps: (1) adjusting the rotation speed of the motor  34  to make the frequency difference between the frame clock Cf 0  and the harmony signal S 0  be equal to zero, and to make the phase difference between the frame clock Cf 0  and the harmony signal S 0  be unequal to zero, where the phase difference can trigger the activating circuit  26  to transmit the activating signal M 0  to the motor  34  to force the motor  34  rotate (i.e. the CD drive  20  is in a constant linear velocity mode and the switch circuit  30  disconnects the output of the sub control circuit  28  from the activating circuit  26  at this time); and (2) after there is a stable phase difference between the frame clock Cf 0  and the harmony signal S 0 , switching the CD drive  20  into a write mode, and then the control circuit  22  further makes the phase difference between the frame clock Cf 0  and the harmony signal S 0  equal to zero, and meanwhile a mode control signal terminal Mode controls the switch circuit  30  to connect the output of the sub-control circuit  28  with the activating circuit  26  so as to force the motor  34  to rotate constantly. In other words, the sub-control circuit  28  records the phase difference when the CD drive  20  is in the constant linear velocity mode so as to drive the motor  34  when the CD drive  20  switches to the write mode. 
     Because the method according to the prior art controls the rotation speed of the motor  34  to adjust the harmony signal S 0  so as to synchronize the harmony signal S 0  with the frame clock Cf 0 , and the CD drive  20  must mechanically switch from the constant linear velocity mode to the write mode to drive the motor  34 , a long response time is required for the CD drive  20  to write data onto the CD  10 . Furthermore, other embedded circuitry of the CD drive  20  is necessary to control the timing to switch the CD drive  20  from the constant linear velocity mode to the write mode, that makes the circuit design of the CD drive  20  more complex. 
     SUMMARY OF INVENTION 
     It is therefore a primary object of the present invention to provide a method and related devices for synchronizing the wobble clock with the writing clock by adjusting the frequency of the writing clock so as to achieving a stable writing state of a compact disk drive quickly. 
     Briefly, the invention provides a method for adjusting signals of a compact disk (CD) drive and synchronizing a wobble clock with a writing clock. The CD drive has a motor for forcing a CD to rotate. The CD has a data track for storing data and a wobble track for recording signals. When the motor forces the CD to rotate, the CD drive generates the wobble clock according to the wobble track, and the CD drive is capable of writing data on the data track according to the writing clock. The method includes adjusting a frequency of the writing clock or a phase of the writing clock to synchronize the writing clock with the wobble clock. 
     These and other objects of the invention will no doubt become obvious to those ordinary skill in the art after reading the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top view of a recordable compact disk. 
         FIG. 2  is a three-dimensional perspective view of the magnified view  1 B of the compact disk. 
         FIG. 3  is a timing diagram of waveforms of related signals of a compact disk drive. 
         FIG. 4  is a function block diagram of a compact disk drive according to the prior art. 
         FIG. 5  is a function block diagram of a compact disk drive according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 5 , which is a function block diagram of a compact disk (CD) drive  40  according to the present invention. The CD drive  40  comprises a control circuit  42 , a motor  54 , and an optical module  52 . The motor  54  is used for forcing the CD  10  to rotate. When the CD  10  rotates over the optical module  52 , the optical module  52  generates a corresponding wobble clock Cb. Additionally, the optical module  52  can write data on the data track  12  according to a writing clock Cw 1 . The control circuit  42  is used for generating the writing clock Cw 1  and a frame clock Cf 1 , which synchronizes with the writing clock Cw 1 , and for making the frame clock Cf 1  synchronize with a harmony signal, which is relatively generated with the wobble clock Cb. 
     The control circuit  42  has a clock generator  46 A and a stabilizing circuit  46 B. The clock generator  46 A comprises a first frequency divider  50 A, a second frequency divider  50 B, a third frequency divider  50 C, a fourth frequency divider  50 D, a phase-locking circuit  48 , a modification circuit  62 , and a debugging circuit  64 . The four frequency dividers  50 A- 50 D are used to divide frequencies of signals by a first ratio N 1 , a second ratio N 2 , a third ratio N 3 , and a fourth ratio N 4  respectively. The phase-locking circuit  48  comprises a phase detector  60 A, a current source  60 B, a low-pass filter  60 C, and voltage-controlled oscillator  60 D. The phase detector  60 A is capable of detecting a phase difference between two input signals. The current source  60 B is capable of generating current, and the magnitude of the current is determined by the phase difference detected by the phase detector  60 A, so that the low-pass filter  60 C can output a corresponding voltage. Finally, the voltage-controlled oscillator  60 D can generate a clock signal, in which the duration of each period corresponds to the voltage received from the low-pass filter  60 C. The stabilizing circuit  46 B comprises two frequency dividers  58 A,  58 B, a phase detector PD, a frequency detector FD, and an activating circuit  56 . 
     The clock generator  46 A of the control circuit  42  receives a system clock Cs that has a plurality of periods with a same interval. The first frequency divider  50 A divides the system clock Cs by the first ratio N 1  to generate a first clock C 1 . The phase-locking circuit  48  generates a third clock C 3 . The third frequency divider  50 C divides the third clock C 3  by the third ratio N 3  to generate the writing clock Cw 1 . The second frequency divider  50 B divides the writing clock Cw 1  by the second ratio N 2  to generate a second clock C 2 . The first clock C 1  and the second clock C 2  are fed back to the phase-locking circuit  48  so that the phase-locking circuit  48  can synchronize the first clock C 1  with the second clock C 2 . Additionally, the fourth frequency divider  50 D is used to divide the second clock C 2  by the fourth ratio N 4  to generate the frame clock Cf 1 . The time duration of one period of the system clock Cs, the first clock C 1 , the second clock C 2 , and the writing clock Cw 1  will later be respectively represented by Ts, T 1 , T 2 , and Tw 1 . Because the phase-locking circuit  48  locks the phases both of the first clock C 1  and the second clock C 2  to synchronize the first clock C 1  with the second clock C 2 , T 1  is equal to T 2 . As previously mentioned, the first frequency divider  50 A generates the first clock C 1  and the second frequency divider  50 B to generate the second clock C 2 , so N 2 ×Tw 1 =T 2  and N 1 ×Ts=T 1 , and then the equation Tw 1 =(N 1 /N 2 )×Ts is obtained. In other words, the period of the writing clock Tw 1  is directly proportional to the period of the system clock Ts, and the ratio of the period of the writing clock Tw 1  to the period of the system clock Ts is defined as a phase-locked rate (i.e. N 1 /N 2 ). Because the period of the system clock Ts is fixed, the period of the writing clock Tw 1  can be easily adjusted by changing the phase-locked rate. Additionally, the frame clock Cf 1  is generated by dividing the writing clock Cw 1  via the second frequency divider  50 B and the fourth frequency divider  50 D. 
     The modification circuit  62  of the clock generator  46 A can repair the waveform of the wobble clock Cb received from the optical module  52  by filtering noise. The debugging circuit  64  is used for generating a harmony signal, which synchronizes with the wobble clock Cb that is repaired by the modification circuit  62 , according to the wobble clock Cb, and adjusting the first dividing ratio N 1  according to the frequency of the wobble clock Cb and the phase difference between the harmony signal and the frame clock Cf 1 . In the stabilizing circuit  46 B, a reference clock Cr is generated by dividing the system clock Cs via the frequency divider  58 A, and a compared clock Cp is generated by dividing the wobble clock Cb via the frequency divider  58 B. The phase detector PD and the frequency detector FS respectively detect the phase difference and the frequency difference between the reference clock Cr and the compared clock Cp, and then output the results to the activating circuit  56  so that the activating circuit  56  can control the rotation speed of the motor  54  via an activating signal terminal M of the activating circuit  56 . 
     The major feature of the present invention is to adjust the frequency of the writing clock Cw 1  for synchronizing and locking the frame clock Cf 1  with the harmony signal, which is generated by the optical module  52 , so as to write data on the correct position of the data track  12 . The frequency divider  58 A of the stabilizing circuit  46 B divides the system clock Cs by a ratio D 1  to generate the reference clock Cr, which is taken as a standard clock signal, so that the compared clock Cp, which synchronizes with the wobble clock Cb, is capable of archiving a steady state gradually according to the reference clock Cr. That means that the motor  54  is controlled to operate with a stable rotation speed. In order to make the rotation speed of the motor  54  stable, it just needs to make the phase difference between the reference clock Cr and the compared clock Cp stable without completely phase-locking the reference clock Cr with the compared clock Cp. In other words, the stabilizing circuit  46 B is capable of controlling the rotation speed of the motor  54  to maintain in a relatively steady state according to the system clock Cs as long as the phase difference between the reference clock Cr and the compared clock Cp is stable. 
     When the motor operates stably, the periods of both the wobble clock Cb and the harmony signal become unchanged. The frequencies and the phases of both the writing clock Cw 1  and the frame clock Cf 1  can be changed according to the wobble Cb and the harmony signal so that the frame clock Cf 1  can be locked with the harmony signal. The debugging circuit  64  generates the corresponding harmony signal according to the wobble clock Cb, and obtains the phase difference between the harmony signal and the frame clock Cf 1 . In other words, the debugging circuit  64  changes the first ratio N 1  of the first frequency divider  50 A according to the frequency of the wobble clock Cb and the phase difference between the harmony signal and the frame clock Cf 1  to synchronize the wobble clock Cb with the writing clock Cw 1 . As previously mentioned, Tw 1 =(N 1 /N 2 )×Ts and the frequency of the writing clock Cw 1  is (N 2 ×N 4 ) times the frequency of the frame clock Cf 1 . In the condition that the period of the system clock Ts is fixed, the period of the writing clock Tw 1  and the frequency of the frame clock Cf 1  can be controlled by changing the first ratio N 1 . After the writing clock Cw 1  is divided by the two frequency dividers  50 B, and  50 D to generate the frame clock Cf 1 , the frame clock Cf 1  is fed back to the debugging circuit  64  so as to adjust both the frequency and the period of the writing clock Cw 1  and the frame clock Cf 1 . Finally, the frame clock Cf 1  and the harmony signal of the debugging circuit  64  are phase locked without any phase difference. For example, when the rotation speed of the motor  54  is too high and causes the frequency of the wobble clock Cb to increase, the debugging circuit  64  detects this situation and then reduces the first ratio N 1  so that the frequencies both of the writing clock Cw 1  and the frame clock Cf 1  increase, and so that the frequency difference between the writing clock Cw 1  and the wobble clock Cb decreases. Similarly, if the frequency of the frame clock Cf 1  is less than the harmony signal, the debugging circuit  64  decreases the first ratio so that the frequency of the writing clock Cf 1  increases and that the frequency difference between the frame clock Cf 1  and the harmony signal reduces. 
     In contrast to the prior art, the present invention method locks the frame clock with the harmony signal by adjusting the frequencies of both the writing clock and the frame clock in the condition that the motor rotates stably. Because the writing clock and the frame clock are generated electrically, there is a shorter response time for controlling operations of the motor compared to the prior art. Moreover, the wobble clock and the writing clock can be phase-locked without changing the rotation speed of the motor, so it becomes simpler to control the operations of the motor. Furthermore, because it is unnecessary to switch the CD drive from the constant linear velocity mode to the write mode, circuit design become easier and reduces the cost of the CD drive. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.