Patent Abstract:
An embodiment of the present invention provides a phase difference detection circuit for detecting a phase difference between input data and an input clock generated based on the input data, including: an input data edge position detecting part detecting an edge position of the input data based on an N-phase clock obtained by dividing a predetermined period into N areas (N is an integer of 2 or more); an input clock edge position detecting part detecting an edge position of the input clock based on the input clock and the N-phase clock; and a phase difference detecting part detecting the phase difference between the input data and the input clock based on the edge position of the input data and an edge position of the input clock.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a phase difference detection circuit, a phase difference detecting method, an optical disk drive, and an optical disk drive controlling method. 
     2. Description of Related Art 
     Nowadays, optical disks such as CD (compact disc) and DVD (digital versatile disc) have been widely available. In addition, new optical disks have been under development. Optical disk drives that read/write information from/to the optical disk amplify and shape signals read through light pick-up to supply read data to a PLL (phase locked loop) circuit. The PLL circuit generates a read clock synchronized with the read data. The read data is extracted in accordance with the synchronized read clock and subjected to signal processing to obtain final reproduction data. 
     At this time, attention should be paid to the fact that data read from the disk involves fluctuation in the time axis direction called “jitter”. The jitter is caused by a reading device inclined with respect to a reading surface of the disk, that is, the optical axis of a reproducing laser beam not vertical to the disk surface, or the laser power inadequate for writing data. In some cases, correct signals cannot be input, leading to an error in reading data or correct data cannot be obtained due to the jitter. 
     Further, a read clock that is generated based on the read data with the jitter involves the jitter. In this case, an important problem is not the jitter in both the read data and the read clock but a relative phase difference. In such a case, even if the jitter of the read data is only detected without considering the jitter of the read clock, the detected jitter is different from a relative phase difference as a practical problem. 
     To that end, a method of detecting a jitter has been under study, and there have been some proposals. As the method of detecting the jitter, there has been proposed a method of inputting a read clock signal the rising/falling edge of which appears concurrently with that of the read data signal and detecting a delay therebetween with a counter (see Japanese Unexamined Patent Publication No. 2001-273715 (Kobayashi), for instance). 
     The related art disclosed in Kobayashi is discussed in brief.  FIG. 10  shows the structure of a jitter detecting device of the related art. The jitter detecting device of the related art generates a read clock of which the edge is synchronous with that of the input read data by means of a PLL circuit  30 , and a phase difference between the read data and the read clock is detected with a phase difference detection circuit  32 . 
     The phase differential signal detected by the phase difference detection circuit  32  is output to a Schmitt circuit  33 . The Schmitt circuit  33  compares the received phase difference with a threshold value preset by a threshold setting register  31 , and sends, if the received phase difference exceeds the threshold value, this comparison result to a counter  34 . The counter  34  increments a count value by 1 when the phase difference exceeds the threshold value. 
     The count value of the counter  34  is recorded in a register  35 . The recorded value is output to a CPU through a CPU interface as needed. It is thus possible to count the number of times the phase difference exceeds the present threshold value. 
     With this method, however, the circuit is operated with reference to the edge of the read data signal, a delay of the read clock signal can be detected but the jitter of the advanced read clock signal cannot be detected. Further, the method only counts the number of times the threshold value is exceeded, thus it is impossible to evaluate the phase difference deviation of the rising edge and falling edge of the read data signal. It is still another problem that the jitter cannot be detected in consideration of the jitter of the read clock signal itself. 
     As mentioned above, the jitter detecting method using the conventional phase difference detection circuit is incapable of detecting the jitter of the advanced read clock signal. As another problem thereof, the jitter cannot be relatively detected in consideration of the influence of the jitter in the read clock signal itself. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a phase difference detection circuit for detecting a phase difference between input data and an input clock generated based on the input data. An input data edge position detector detects an edge position of the input data based on an N-phase clock (N is an integer of 2 or more). An input clock edge position detector detects an edge position of the input clock based on the input clock and the N-phase clock. A phase difference detector detects the phase difference between the input data and the input clock based on the edge position of the input data and the edge position of the input clock. According to this circuit configuration, edge positions of both of input data and an input clock are detected, making it possible to obtain jitters of both of the input data and the input clock to calculate a relative jitter. 
     Another aspect of the present invention provides a phase difference detecting method for detecting a phase difference between input data and an input clock generated based on the input data. An edge position of the input data is detected based on an N-phase clock. An edge position of the input clock is detected based on the input clock and the N-phase clock. The phase difference between the input data and the input clock is detected based on the detected edge position of the input data and the detected edge position of the input clock. According to this method, edge positions of both of input data and an input clock are detected, making it possible to obtain jitters of both of the input data and the input clock to calculate a relative jitter. 
     According to the present invention, it is possible to provide a phase difference detection circuit capable of detecting edge positions of both input data and input clock to detect a jitter of the input data relative to a jitter of the input clock. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing the configuration of a phase difference detection circuit according to the present invention; 
         FIG. 2  is a block diagram showing the configuration of a data rising edge detection circuit according to the present invention; 
         FIG. 3  is a timing chart showing rising/falling timings of read data and clock signals of read clock and N-phase clock according to the present invention; 
         FIG. 4  shows a relationship between edge values input to an edge position encoding circuit and output encoded-data according to the present invention; 
         FIG. 5  shows a relationship between a subtraction result and generated difference data according to the present invention; 
         FIG. 6  is a block diagram showing the configuration of a subtracter according to the present invention; 
         FIG. 7  is a timing chart showing a processing flow for a read data signal, a read clock signal, N-phase clock signal, detected edge positions, and output phase differences according to the present invention; 
         FIG. 8  is a graph showing a relationship between the inclination of an optical disk and a phase difference of a read data signal according to the present invention; 
         FIG. 9  is a block diagram showing the configuration of an optical disk device according to the present invention; and 
         FIG. 10  shows the configuration of a jitter detecting device of the related art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed. 
     First Embodiment of the Invention 
       FIG. 1  shows the overall configuration of a phase difference detection circuit according to the present embodiment. A phase difference detection circuit  1  includes a PLL circuit  10 , a data rising edge detection circuit  11 , a data falling edge detection circuit  12 , a clock falling edge detection circuit  13 , edge position encoding circuits  14 ,  15 , and  16 , subtracters  17 ,  18 , and a memory  19 . 
     The PLL circuit  10  receives a read data signal to generate a read clock signal synchronous with the rising/falling edge of the received read data signal. The generated read clock signal is output to a clock falling edge detection circuit  13 . 
     The data rising edge detection circuit  11  receives the read data signal and an N-phase clock signal to detect a rising edge position of the received read data signal with reference to the received N-phase clock signal. The N-phase clock signal consist of N types of signals having the same cycle as the read clock signal and the phases of which are shifted from one another by 360°/N. Here, N is an integer of 2 or more, preferably, 2 to the Mth power (M is an integer of 1 or more) such as 2, 4, 8, and 16. In the embodiment of the present invention, N=8. The method of detecting the edge based on the N-phase clock signal is detailed later. Information about the detected edge position is sent to the edge position encoding circuit  14 . 
     The data falling edge detection circuit  12  receives the read data signal and the N-phase clock signal to detect a falling edge position of the received read data signal based on the received N-phase clock signal. Information about the detected edge position is output to the edge position encoding circuit  15 . 
     The clock falling edge detection circuit  13  receives the read clock signal and the N-phase clock signal to detect the falling edge position of the received read clock signal based on the received N-phase clock signal. The read clock signal is generated by the PLL circuit  10 . Information about the detected edge position is sent to the edge position encoding circuit  16 . 
     The edge position encoding circuits  14 ,  15 , and  16  encode the received information about the edge positions. An encoding method is described in detail later. The encoded data are output to the subtracters  17  and  18 . 
     The subtracter  17  generates difference data of the edge position encoded data supplied from the edge position encoding circuits  14  and  16 , and the subtracter  18  generates difference data of the edge position encoded data supplied from the edge position encoding circuits  15  and  16 . The generated difference data are sent to the memory  19 . 
     The memory  19  stores the difference data supplied from the subtracters  17  and  18 . The stored difference data are output in response to a request from a CPU or other such units. 
     Subsequently, a method of detecting a rising edge position of the read data signal with the data rising edge detection circuit  11  is described.  FIG. 2  shows the configuration of the data rising edge detection circuit  11  according to the present invention. The data rising edge detection circuit  11  includes variation point detection circuits  110  to  117 , and an arithmetic logical circuit  118 . 
     Specifically, for example, the variation point detection circuit  110  receives a signal CLK 0  of the N-phase clock signal, and determines whether or not the rising edge of the separately received read data signal falls within an area of the CLK 0 . If the determination result is positive, “1” is sent to the arithmetic logical circuit  118  as DATA 0 ; otherwise, “0” is sent. The same applies to the remaining variation point detection circuits  111  to  117  except for the received signals of the N-phase clock signal. 
     The arithmetic logical circuit  118  executes arithmetic operation based on the respective data from the variation point detection circuits  110  to  117  to output the arithmetic operation result as EDGE 0  to EDGE 7 . The arithmetic operation as illustrated in the arithmetic logical circuit  118  of  FIG. 2  is executed. For example, EDGE 0  is 1 when DATA 0  is 1, and DATA 7  and DATA 1  are 0; otherwise, EDGE 0  is 0. Similarly, each EDGE takes 1 only when corresponding DATA is 1, and adjacent DATA values are 0; otherwise, EDGE takes 0. 
     As describe above, the variation point detection circuits  110  to  117  each detects a logical level of the input data at each clock edge of the N-phase clock. The arithmetic logical circuit  118  determines the kth (k is an integer) clock of the N-phase clock as an edge timing of the input data if the kth variation point detection circuit detects HIGH and the (k−1)th and the (k+1)th detection circuits detect LOW. 
     Detailed description thereof is given taking a specific example.  FIG. 3  is a timing chart showing timings of rising/falling edges of read data and signals of the N-phase clock signal. In the illustrated example of  FIG. 3 , the first rising edge of the read data appears between the rising edges of CLK 2  and CLK 3  of the N-phase clock. In this case, DATA 3  and subsequent DATA&#39;s show pulse rises in sync with the rising edges of CLK 3  and subsequent CLK&#39;s, and the values thereof are output from the variation point detection circuits  110  to  117  to the arithmetic logical circuit  118 . Then, as a result of the logical operation of the arithmetic logical circuit  118 , EDGE 3  takes 1, and the remaining EDGE&#39;s take 0. Likewise, on the second rising edge, EDGE 6  takes 1, and the remaining EDGE&#39;s take 0. 
     In this way, the data rising edge detection circuit  11  can determine an area where the rising edge of the target read data signal appears from among the areas divided according to the N-phase clock signal, and output the determination result as bit data. 
     The data falling edge detection circuit  12  and the clock falling edge detection circuit  13  have the same circuit configuration as the data rising edge detection circuit  11  except that the detecting position for the variation point is changed to the falling edge of the read data and the falling edge of the read clock data. 
     The edge positions detected with the data rising edge detection circuit  11 , the data falling edge detection circuit  12 , and the clock falling edge detection circuit  13  are sent as the bit data to the edge position encoding circuits  14 ,  15 , and  16 , respectively. The edge position encoding circuits  14 ,  15 , and  16  encode the received bit data about the edge position. 
       FIG. 4  shows a relationship between the values of the EDGE 0  to EDGE 7  input to the edge position encoding circuits  14 ,  15 , and  16  and the output encoded-data. The EDGE 0  to EDGE 7  can be encoded into 3-bit data since one of them is 1 and the rest are 0, which means 8 patterns in total. 
     The encoded data generated with the edge position encoding circuits  14 ,  15 , and  16  are supplied to the subtracters  17  and  18 , and the subtracters  17  and  18  generate difference data. The subtracter  17  generates difference data representative of a difference between rising edge position encoded data of the read data signal from the edge position encoding circuit  14  and falling edge position encoded data of the read clock signal from the edge position encoding circuit  16 . The subtracter  18  generates difference data representative of a difference between falling edge position encoded data of the read data signal from the edge position encoding circuit  15  and falling edge position encoded data of the read clock signal from the edge position encoding circuit  16 . As a result thereof, the relative difference data between the read data signal and the read clock signal can be obtained. Further, it is possible to deal with the case where the N-phase clock involves the jitter. For example, if the N-phase clock has the jitter of Δ, the calculation is such that (read data edge+Δ)−(read clock edge +Δ)=(read data edge)−(read clock edge), so the jitter of the N-phase clock can be cancelled out. 
       FIG. 5  shows the relationship between the subtraction result and the generated difference data. When N=8, the maximum absolute value of the phase difference is 4. Thus, if the calculation result is 5, the absolute value of the phase difference is 3. If the subtraction result is 6, the absolute value of the phase difference is 2. If the subtraction result is 7, the absolute value of the phase difference is 1. 
     If N is 2 to the Mth power (M is an integer of 1 or more) such as 8 or 16, the subtracters  17  and  18  can be configured as shown in  FIG. 6 . The subtracter  17  includes a subtracter circuit  170 , an all-bit inverter circuit  171 , a +1 adder circuit  172 , and a selector  173 . 
     The subtracter circuit  170  executes the subtraction processing on the received two encoded data about the edge position to send the subtraction result to the all-bit inverter circuit  171  and the selector  173 . The all-bit inverter circuit  171  executes the bit-inversion on the received encoded data to output the bit-inverted data to the +1 adder circuit  172 . The +1 adder circuit  172  adds 1 to the data supplied from the all-bit inverter circuit  171  to send the addition result to the selector  173 . In the case of N=8, the selector  173  selects, if the subtraction result from the subtracter circuit  170  is 4 or less, the subtraction result received from the subtracter circuit  170 , and selects, if the result is more than 4, the addition result received from the +1 adder circuit  172  to send the selected one to the memory  19 . Provided that N=16, the selector  173  selects a desired one depending on whether or not the subtraction result is 8 or less. 
     Owing to such a circuit configuration, the subtracters  17  and  18  can send the phase difference calculated on the basis of the subtraction result of  FIG. 5  to the memory  19 . 
     The memory  19  stores the phase difference data received from the subtracters  17  and  18  as 3-bit data (if N=8). The stored phase difference data are read in response to a request from a CPU or other such units on the other end. There is no particular limitation on the application of the stored phase difference data. 
       FIG. 7  is a timing chart showing a processing flow for a read data signal, a read clock signal, N-phase clock signal, detected edge positions, and output phase differences. On the first rising edge edgeT 1  of the read data, the rising edge position is “3”, and the corresponding falling edge position of the read clock is “5”, so the phase difference equals “2”. Likewise, on the first falling edgeT 2  of the read data, the falling edge position is “2”, and the corresponding falling edge position, which is different from the above corresponding falling edge position, of the read clock is “5”, so the phase difference is “3”. 
     On the second rising edgeT 3  of the read data, the rising edge position is “0”, and the corresponding falling edge position of the read clock is “6”, so the difference equals −6, but the actual phase difference becomes “2” with the use of the subtracter  17 . On the second falling edgeT 4  of the read data, the falling edge position is “6”, and the corresponding falling edge position of the read clock is “6”, so the phase difference equals “0”. 
     According to this configuration, the rising edge and the falling edge of the read data can be determined with respect to the falling edge of the read clock, so the phase difference reflecting the jitter of the read clock can be obtained. In addition, the phase difference is calculated separately on the rising edge and the falling edge, so more accurate phase difference data can be offered. 
     Second Embodiment of the Invention 
     A description is given of an example in which the phase difference detection circuit of the present invention is applied to an optical disk device. The optical disk device is known to largely vary a phase difference of a read data signal upon, for example, data reproduction due to the inclination of a reading device with respect to a reading surface of the disk.  FIG. 8  shows the relationship between the inclination of the reading device with respect to the reading surface of the disk, and the phase difference of the read data signal. To minimize the error resulting from the phase difference, it is necessary to find a point of the graph of  FIG. 8 , at which the phase difference is minimized. The phase difference detection circuit of the present invention is applicable to the optical disk device for that purpose. 
       FIG. 9  is a schematic diagram focused on the structure related to the phase difference detection circuit of the present invention in the optical disk device of the present invention. The optical disk device  2  includes a CPU  20 , a CPU interface  201 , a memory  21 , a memory interface  211 , a phase difference detection circuit  22 , a PLL circuit  23 , an N-phase clock generator circuit  231 , a data comparator  24 , a motor driver  25 , a laser driver  251 , an RF amplifier  26 , a pick-up  27 , a spindle motor  28 , and a digital servo processor  29 . 
     The CPU  20  executes various types of control over the optical disk device  2 . The CPU interface  201  controls the data exchange between the CPU  20  and the memory interface  211 , the phase difference detection circuit  22 , the PLL circuit  23 , or the data comparator  24 . 
     Programs for controlling the optical disk device  2  or various types of data are recorded/read on/from the memory  21 . The memory interface  211  controls the data exchange among the memory  21 , the CPU  20 , and the phase difference detection circuit  22 . 
     The phase difference detection circuit  22  detects the phase difference between the received read data signal and read data clock. The phase difference detection circuit has the same configuration as that of the first embodiment of the present invention as shown in  FIG. 1 , but the PLL circuit  10  of  FIG. 1  may be replaced by the PLL circuit  23 , and the memory  19  may be replaced by the memory  21 , both of which may be omitted from the phase difference detection circuit  22  of the present invention. The phase difference detecting method is the same as the first embodiment of the present invention. 
     The PLL circuit  23  generates and outputs read clock signals based on the read data signal received from the data comparator  24  to the phase difference detection circuit  22  and the N-phase clock generator circuit  231 . 
     The N-phase clock generator circuit  231  receives the read clock signal from the PLL circuit  23  to generate N-phase clock based on the received read clock signal. The N-phase clock generator circuit  231  sends the generated N-phase clock to the phase difference detection circuit  22 . 
     The data comparator  24  slices the RF signals received from the RF amplifier  26  at a given slice level into binary data. This binary data is the read data signal. The generated read data signal is sent to the phase difference detection circuit  22  and the PLL circuit  23 . 
     The motor driver  25  controls the rpm of the spindle motor  28  based on rotational servo signals supplied from the digital servo processor  29 . Besides, the motor driver  25  controls the pick-up  27  based on a tracking servo signal and focus servo signal received from the digital servo processor  29 . 
     The laser driver  251  controls the pick-up  27  based on the correction amount from the CPU  20  to adjust the laser power. 
     The RF amplifier  26  amplifies and applies the beam shaping to the signals received from the pick-up  27  to generate and send RF signals to the data comparator  24 . 
     The pick-up  27  reads the data from the optical disk under the control of the motor driver  25  to send the read signal to the RF amplifier  26 . The spindle motor  28  rotates the optical disk under the control of the motor driver  25 . 
     The digital servo processor  29  generates and sends rotational servo signals, tracking servo signals, and focus servo signals to the motor driver  25  under the control of the CPU. 
     Subsequently, the application of the phase difference detected by the phase difference detection circuit  22  is described. The phase difference data supplied from the phase difference detection circuit  22  is stored in the memory  21 . The phase difference data stored in the memory  21  is sent to the CPU  20 , and the CPU  20  executes various types of control based on the phase difference data. 
     Examples of the control include, in addition to the foregoing adjustment of the inclination of the reading device with respect to the disk&#39;s reading surface, control of the laser power for writing the data to the optical disk. The data is written to the optical disk through turn on/off of the laser, so the laser power significantly influences the recording quality. Unless the optimum laser power is used, the obtained data of the read data signal is distorted, so the offset occurs on the edge. How far the data is distorted varies depending on the quality of the optical disk, so it is necessary to adjust the laser power so as to deal with various recording mediums. For that purpose, the phase difference detection circuit  22  detecting the deviation on the edge can be used. 
     The laser power is adjusted such that the CPU  20  sends the correction amount data to the laser driver  251  based on the received phase difference data. Receiving the correction amount data from the CPU  20 , the laser driver  251  adjusts the laser power based on the correction amount data. 
     The phase difference data can be used for adjusting the RF signals. In this case, the CPU  20  adjusts the settings of a DC level of the RF amplifier  26 , gain, or an output current of a driver. 
     Similarly, the correction amount data based on the phase difference is converted into analog data, enabling various types of control. In this case, the correction amount is sent to the digital servo processor  29  based on the phase difference data received from the CPU  20 . The digital servo processor  29  converts the received correction amount data into analog data to be sent to the motor driver  25 . The motor driver  25  controls the spindle motor  28  based on the received correction amount. Further, the motor driver  25  controls the pick-up  27  based on the received correction amount. In this way, the pick-up  27  and the spindle motor  28  are controlled, making it possible to control tracking or focusing processings or adjust the reading device with respect to the disk&#39;s reading surface based on the detected phase difference. 
     Other Embodiment of the Invention 
     In the above example, the phase difference data is recorded as the absolute value of 0 to 4 but may be recorded as a signed relative phase difference. 
     Further, in the above example, the N-phase clock is generated based on the input read clock data but maybe generated based on other clock generated inside an LSI or may be externally applied. In addition, the N-phase clock signal has N types of signals whose phases are shifted from one another by 360°/N. However, the degree of phase shift is not particularly limited insofar as it is determined which of N divided areas the edge appears in. 
     In addition, in the above example, the phase difference is calculated based on the falling edge of the read clock signal, the rising and falling edges of the read data signal but may be calculated based on the rising edge of the read clock signal, and the rising and falling edges of the read data signal. 
     It is apparent that the present invention is not limited to the above embodiment and it may be modified and changed without departing from the scope and spirit of the invention.

Technology Classification (CPC): 6