BACKGROUND
The present invention relates to a wobble signal synthesizer, and more specifically, to a wobble signal synthesizer for generating a wobble signal synchronized with physical wobble signal through comparing phases of both land pre-pit signal and synthesized wobble signal with a reference clock.
Conventionally, an optical recordable disc, such as CD−R(W), DVD−R(W), or DVD+R(W) has been widely utilized as a medium for recording data. Wobbling grooves are formed in a data-recording region of the blank disc such that they meander slightly to produce a physical wobble signal on the groove of a disc surface to provide a signal reference for disc rotation control or for clock recovery purpose. Data in the form of pit-land mark is recorded inside this wobble groove. In other words, the wobble groove defines a recording track. It is well known that the optical disc drive has a pick-up head, and the pick-up head is divided into four parts to receive reflected light from surface of the optical disc. The reflected light received by two parts in the same side are transformed into electrical signals and summed up respectively. Then differential push-pull process is performed to generate a sinusoidal signal, named extracted wobble signal. If there is a land pre-pit across the wobble groove, such as DVD−R(W) disc, a peak pulse will piggyback on the extracted wobble signal. By feeding the extracted push-pull signal into a slicer, the position of the land pre-pit is confirmed and the signal outputted from the slicer is named as land pre-pit signal.
When recording data onto this recording track, the wobble signal is detected from the wobble groove so as to control disc rotation and to generate a recording clock. Then, data can be appropriately recorded at a target recording position through decoding physical address information carried on land pre-pit signals(such as DVD−R(W)) or modulated wobble signals(such as CD−R(W) and DVD+R(W)).
Taking DVD−R(W) disc for example, the specification suggests that the center of 14T data sync signal need to be close with the first land pre-pit signal within the range of +7T˜−7T distance. In order to have good recording performance, disc rotation must synchronize with the recording clock. However, the information recording capacity of a DVDR(W) is much higher than the capacity of a conventional CD−R(W) disc, a track pitch of a DVD (which is a center-to-center distance between neighboring wobble grooves in the radial direction) is smaller than a track pitch of a CD−R disc. In a DVD, because of the smaller track pitch, the crosstalk of neighboring wobble grooves is not negligible.
In certain circumstances, when recording data onto a DVD, the extracted wobble signal (which is obtained from the DVD) may have significant variances in amplitude and phase due to the crosstalk of neighboring wobble grooves. When the crosstalk occurs due to the adjacent wobble grooves, the extracted wobble signal is interfered with by the wobble component generated from the adjacent wobble groove so that the amplitude and the phase will deviate, that is, the extracted wobble signal read by a optical disc drive does not exactly match to the physical wobble signal on the disc surface. In this case, it is difficult to produce a recording clock that is precisely synchronized with the rotation of the disc, if the recording clock is produced directly based on the extracted wobble signal.
In particular, the time delay and signal distortion of the processing circuits results in a mismatch between the extracted wobble signal and physical wobble signal. This mismatch effect causes a deviation in a disc rotation control signal because of a phase difference between the physical wobble signal recorded by wobble grooves on the optical disc and the extracted wobble signal generated from processing the extracted operation. Because the extracted wobble signal is corresponding to the clock signal generation and the physical wobble signal is corresponding to the position of the rotation of the disc, the phase of the clock signal is deviated from the phase of the rotation of the disc. Such a deviation causes the recording pits to be inaccurately formed on the recording track and degrades performance of the optical disc drive. For example, when recording data on the disc, the positions or lengths of the recorded pits are inaccurate as mentioned above. In this case, this will cause errors while reproducing information in accordance with the recorded pits, and greatly degrade the recording and reproducing quality.
In our invention, we provide a circuit architecture and method for generating a synthesized wobble signal synchronized with physical wobble signal for the optical disc drive to circumvent the effect of crosstalk or other non-ideal interference factors.
SUMMARY
According to the claimed invention, a wobble signal synthesizer for generating a synthesized wobble signal synchronized with physical wobble signal is disclosed. The wobble signal synthesizer includes a variable-period signal generating module for generating the synthesized wobble signal; a first period calculating module, electrically coupled to the variable-period signal generating module, for calculating the number of periods of a second reference clock in a certain period of the synthesized wobble signal; a second period calculating module for calculating the number of periods of the second reference clock in a certain wobble period at a disc rotation speed; a comparison module, electrically coupled to the variable-period signal generating module, the first period calculating module, and the second period calculating module, for outputting the period error value; and a phase alignment module, electrically coupled to the variable-period signal generating module, for determining the phase error value.
According to the claimed invention, a method for generating a synthesized wobble signal synchronized with physical wobble signal is further disclosed. The method includes generating the synthesized wobble signal according to a first reference clock, a phase error value, and a period error value; calculating the number of periods of a second reference clock in certain period of the synthesized wobble signal to produce a first period number; calculating the number of periods of the second reference clock in a certain wobble period at a disc rotation speed to produce a second period number; determining the period error value according to the first and second period numbers; and determining the phase error value between a land pre-pit signal and the synthesized wobble signal.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a wobble signal synthesizer according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a wobble signal synthesizer according to a second embodiment of the present invention.
FIG. 3 is a block diagram of a period decision circuit illustrated in FIG. 2.
FIG. 4 is a block diagram of a wobble signal synthesizer according to a third embodiment of the present invention.
FIG. 5 is a block diagram of a wobble period searching circuit illustrated in FIG. 4.
FIG. 6 is a block diagram of a wobble signal synthesizer according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION
Please refer to FIG. 1. FIG. 1 is a block diagram of a wobble signal synthesizer 10 according to a first embodiment of the present invention. The wobble signal synthesizer 10 is able to generate a synthesized wobble signal WS synchronized with a physical wobble signal on the surface of an optical disc by means of correcting the phase relation with detected physical land pre-pit. The wobble signal synthesizer 10 includes a variable-period signal generator 80 for generating a reference wobble signal Wref according to a first reference clock Cr1 and a period error value Epe; a tuning delay circuit 70, electrically coupled to the variable-period signal generator 80, for adjusting phase of the reference wobble signal Wref according to a phase error value Eph to generate the synthesized wobble signal WS; a first period calculating module 50, electrically coupled to the tuning delay circuit 70, for calculating the number of periods of a second reference clock Cr2 in one period of the synthesized wobble signal WS to produce a first period number N1; a second period calculating module 30 for calculating the number of periods of the second reference clock Cr2 in one period of the extracted wobble signal WE to produce a second period number N2; a comparison module 40, electrically coupled to the variable-period signal generator 80, the first period calculating module 50, and the second period calculating module 30, for outputting the period error value Epe, determined in accordance with the first and the second period numbers N1, N2, to the variable-period signal generator 80; and a phase alignment module 60, electrically coupled to the tuning delay circuit 70, for determining the phase error value Eph according to a land pre-pit signal Spre-pit and the synthesized wobble signal WS, wherein the land pre-pit signal Spre-pit is generated by detecting a center of a land pre-pit from a push-pull signal. Due to the pre-pit peak always appears on the physical wobble signal at regular phase, so the phase error between the synthesized wobble signal WS and the land pre-pit signal Spre-pit is capable of adjusting the phase error between the synthesized wobble signal WS and the physical wobble signal. Please note that the tuning delay circuit 70 and the variable-period signal generator 80 are combined to form a variable-period signal generating module 20.
In this embodiment, the variable-period signal generator 80 receives a high-frequency source signal, the first reference clock Cr1, and multiplies a period of the first reference clock Cr1 by a factor determined by the period error value Epe to determine a period of the reference wobble signal Wref. If the period error value Epe shows the period of the extracted wobble signal WE is less than the period of the synthesized wobble signal WS, i.e. N2 is smaller than N1, then the variable-period signal generator 80 decreases the factor for reducing the period of the reference wobble signal Wref to match the period of the extracted wobble signal WE. Otherwise, the variable-period signal generator 80 increases the factor for increasing the period of the reference wobble signal Wref to match the period of the extracted wobble signal WE. Next, the tuning delay circuit 70 adjusts phase of the reference wobble signal Wref according to the phase error value Eph to generate the synthesized wobble signal WS. In a DVD-R disc, it is well known that some land pre-pits stride across adjacent wobble tracks on the surface of the disc to illustrate the address information. According to the well-known land pre-pit characteristics, the phase alignment module 60 determines the phase error value Eph according to the land pre-pit signal Spre-pit. Please note that the first and second reference clocks Cr1, Cr2 are allowed to be the same to reduce the circuit complexity of the wobble signal synthesizer 10.
Please refer to FIG. 2. FIG. 2 is a block diagram of a wobble signal synthesizer 110 according to a second embodiment of the present invention. The wobble signal synthesizer 110 includes a variable-period signal generator 170 for generating a synthesized wobble signal WS according to a first reference clock Cr1 and a period-adjusting signal Vadj; a period decision circuit 180, electrically coupled to a comparison module 140 and a phase alignment module 160, for generating the period-adjusting signal Vadj according to a phase error value Eph and a period error value Epe; a first period calculating module 150, electrically coupled to the variable-period signal generator 170, for calculating the number of periods of a second reference clock Cr2 in one period of the synthesized wobble signal WS to produce a first period number N1; a second period calculating module 130 for calculating the number of periods of the second reference clock Cr2 in one period of the extracted wobble signal WE to produce a second period number N2; a comparison module 140, electrically coupled to the period decision circuit 180, the first period calculating module 150, and the second period calculating module 130, for outputting the period error value Epe determined in accordance with the first and second period numbers N1, N2 to the period decision circuit 180; and a phase alignment module 160, electrically coupled to the period decision circuit 180, for determining the phase error value Eph according to the land pre-pit signal Spre-pit and the synthesized wobble signal WS. Similar to the first embodiment shown in FIG. 1, the variable-period signal generator 170 and the period decision circuit 180 are combined to act as a variable-period signal generating module 120 and the land pre-pit signal Spre-pit is generated by detecting a center of a land pre-pit peak of the extracted wobble signal WE.
It can be easily seen that the difference between the first and second embodiments is the configuration of the variable-period signal generating module. In the first embodiment, the variable-period signal generating module 20 processes the period error value Epe and the phase error value Eph separately in two circuit blocks, i.e. the variable-period signal generator 80 and the tuning delay circuit 70. In the second embodiment, however, the variable-period signal generating module 120 processes the period error value Epe and the phase error value Eph in the same circuit block, i.e. the period decision circuit 180.
There are many ways to implement the period decision circuit 180, and an example for illustrative purposes is disclosed as follows. Please refer to FIG. 3. FIG. 3 is a block diagram of the period decision circuit 180 shown in FIG. 2. The period decision circuit 180 includes a first mapping unit 181, electrically coupled to the phase alignment module 160, for converting the phase error value Eph into a first tuning value Vt1; a second mapping unit 182, electrically coupled to the comparison module 140, for converting the period error value Epe into a second tuning value Vt2; a switching unit 183, electrically coupled to the first and second mapping units 181 and 182, for selectively utilizing either the first tuning value Vt1 or the second tuning value Vt2 as an output according to a control signal SC; a decision logic 184, electrically coupled to the switching unit 183, for generating the control signal SC; and an accumulation unit 185, electrically coupled to the switching unit 183, for accumulating the output of the switching unit 183 to determine the period-adjusting signal Vadj. In this embodiment, the control signal SC controls the switching unit 183 to select the first tuning value Vt1 as the output when the period error value Epe falls in a target range, and the control signal SC controls the switching unit 183 to select the second tuning value Vt2 as the output when the period error value Epe does not fall in the target range. In short, the period decision circuit 180 firstly adjusts the period of the period-adjusting signal Vadj according to the period error value Epe when the period error between the synthesized wobble signal WS and the extracted wobble signal WE is acceptable (i.e. the period error value Epe falls in the target range). Then, the period decision circuit 180 turns to adjust the phase of the period-adjusting signal Vadj according to the phase error value Eph.
Please refer to FIG. 4. FIG. 4 is a block diagram of a wobble signal synthesizer 210 according to a third embodiment of the present invention. The wobble signal synthesizer 210 includes a variable-period signal generator 280 for generating a reference wobble signal Wref according to a first reference clock Cr1 and a period error value Epe; a tuning delay circuit 270, electrically coupled to the variable-period signal generator 280, for adjusting phase of the reference wobble signal Wref according to a phase error value Eph to generate the synthesized wobble signal WS; a first period calculating module 250, electrically coupled to the tuning delay circuit 270, for calculating the number of periods of a second reference clock Cr2 in one period of the synthesized wobble signal WS to produce a first period number N1; a pre-pit measurement circuit 231 for detecting a time interval IN between two land pre-pits; a period calculator 232 for predicting period of the extracted wobble signal according to position P and rotation speed S of optical pick-up head, and producing a reference period number Nref; a wobble period searching circuit 233, electrically coupled to the pre-pit measurement circuit 231, the period calculator 232, and a comparison module 240, for determining the second period number N2 according to the interval IN determined by the pre-pit measurement circuit 231 and the reference period number Nref determined by the period calculator 232; a comparison module 240, electrically coupled to the variable-period signal generator 280, the first period calculating module 250, and the wobble period searching circuit 233, for outputting the period error value Epe determined in accordance with the first and second period numbers N1, N2 to the variable-period signal generator 280; and a phase alignment module 260, electrically coupled to the tuning delay circuit 270, for determining the phase error value Eph according to the land pre-pit signal Spre-pit and the synthesized wobble signal WS. Please note that the pre-pit measurement circuit 231, the wobble period searching circuit 233, and the period calculator 232 are combined to form a function block called the second period calculating module 230. As shown in FIG. 4, the land pre-pit signal is transmitted into the pre-pit measurement circuit 231, the pre-pit measurement circuit 231 detects two nearby land pre-pits and measures the time interval IN between two nearby land pre-pits. Reference period number of one equivalent wobble signal period is able to be predicted through a lookup table based on position and rotation speed of the optical pick-up head; therefore, the period of equivalent wobble signal is determined through detecting the interval IN.
From comparing FIG. 4 with FIG. 1, it is obvious that the difference between the two diagrams is the configuration of the second period calculating module. FIG. 1 can be applied to any types of calculators to calculate the number of periods of the second reference clock Cr2 in one period of the extracted wobble signal WE to produce the second period number N2. However, in FIG. 4, the pre-pit measurement circuit 231 detects the interval IN between two land pre-pits. Because the specification promises integer numbers of physical wobble periods placed between two land pre-pit signals, the interval IN, therefore, represents a plurality of periods of the wobble signals. The objective of the period calculator 232 is to provide an initial, referable reference period number of one equivalent wobble signal. Then, the wobble period searching circuit 233 is able to determine the precise period number, second period number N2, according to the interval IN and the reference period number Nref. Please note that it is possible to remove the period calculator 232 from the second period calculating module 230. For this case, the wobble period searching circuit 233 determines the second period number N2 only according to the interval IN and the second reference clock Cr2. The benefit of utilizing the period calculator 232 is increasing the accuracy of the second period number N2.
The above-mentioned wobble period searching circuit 233 in particular works more efficiently if implemented by digital circuits. Please refer to FIG. 5. FIG. 5 is a block diagram of the wobble period searching circuit 233 shown in FIG. 4. The wobble period searching circuit 233 includes a first divider 234 for dividing the interval IN by the reference period number Nref to determine an integer quotient QI and a fractional quotient QF; a quotient logic 235, electrically coupled to the first divider 234, for determining a target integer quotient QT according to the integer quotient QI and a fractional quotient QF; and a second divider 236, electrically coupled to the quotient logic 235, for dividing the interval IN by the target integer quotient QT to determine the second period number N2. Firstly, the first divider 234 divides the interval IN by the reference period number Nref to obtain the integer quotient QI and the fractional quotient QF. Because the reference period number Nref is an initial, predicted value, the fractional quotient QF is referenced to further tune the integer quotient QI. In other words, the smaller the fractional quotient QF is, the more accurate the reference period number Nref. Next, the quotient logic 235 compares the fractional quotient QF with an upper limit and a lower limit. If the fractional quotient QF is greater than the upper limit, the quotient logic 235 adds one to the integer quotient, i.e. QI+1, as the target integer quotient QT; if the fractional quotient QF is less than a lower limit, the quotient logic 235 sets the integer quotient QI as the target integer quotient QT; and if the fractional quotient QF is between the upper limit and the lower limit, the quotient logic 235 abandons the integer quotient QI and the fractional quotient QF, and then re-determines the target integer quotient QT. Finally, the second divider 236 divides the interval IN by the target integer quotient QT to obtain a precise second period number N2 that stands for the number of periods of the second reference clock Cr2 in one period of the extracted wobble signal WE.
One advantage of the wobble signal synthesizer 210 is that the wobble period searching circuit 233 is capable of determining the second period number N2 by averaging a plurality of calculated period numbers corresponding to different periods of the land pre-pit signals. For example, the wobble period searching circuit 233 determines a first number N21 according to the first interval IN1, and the first reference period number Nref1, a second number N22 according to the second interval IN2 and the second reference period number Nref2, and a third number N23 according to the third interval IN3 and the third reference period number Nref3. Then the wobble period searching circuit 233 averages the first number N21, the second number N22, and the third number N23 to output the wanted second period number N2. Therefore, the influence caused by jitters or noise is greatly reduced and the accuracy of the second period number N2 is further increased.
Please note that the wobble period searching circuit 233 discussed above is not limited in digital or analog circuits. In fact, if digital circuits construct the wobble period searching circuit 233, it is easier to be accomplished via applying a processor connecting with a storage unit. The storage unit storing a searching program has the ability to calculate the second period number N2. The processor then only has to execute the searching program to determine the second period number.
Please refer to FIG. 6. FIG. 6 is a block diagram of a wobble signal synthesizer 310 according to a fourth embodiment of the present invention. The wobble signal synthesizer 310 includes a period decision circuit 380, a variable-period signal generator 370, a first period calculating module 350, a comparison module 340, a phase alignment module 360, an pre-pit measurement circuit 331, a wobble period searching circuit 333, and a period calculator 332. The pre-pit measurement circuit 331, the wobble period searching circuit 333, and the period calculator 332 are combined to form a second period calculating module 330.
Comparing embodiments shown in FIG. 2 and FIG. 6, the only difference is the second period calculating module. Due to functions of other blocks in FIG. 6 being the same as those in FIG. 2, further description of these other blocks is omitted for brevity. In this embodiment, the operation of the second period calculating module 330 shown in FIG. 6 is the same as the second period calculating module 230 shown in FIG. 4. That is, the wobble signal synthesizer 310 in the fourth embodiment is established from the wobble signal synthesizer 110 by replacing the second period calculating module 130 with the second period calculating module 230 shown in FIG. 4.
Due to dynamically comparing the period error and phase error between the synthesized wobble signal, the extracted wobble signal and the land pre-pit signal, the synthesized wobble signal is tuned immediately. Moreover, because the synthesized wobble signal is generated by an independent, high frequency reference clock, and not by the extracted wobble signal directly, the wobble signal synthesizer can be constructed by digital circuits, meaning that the digital control is utilized. Thus, the wobble signal synthesizer is capable of averaging a plurality of periods of the extracted wobble signal to generate the synthesized wobble signal, which reduces jitters or noise effect and increases the performance of the synthesized wobble signal.
Because the extracted wobble signal WE is directly extracted from surface of the optical disc, the phase is interfered by the crosstalk. However, the frequency is not interfered by the crosstalk, still remains the same to the physical wobble signal. It is therefore the present invention utilizes the extracted wobble signal WE to be a reference signal to calibrate the synthesized wobble signal WS, additionally, the land pre-pit signal represents the rotation velocity of the optical disc, so the land pre-pit signal is also capable of synchronizing the extracted wobble signal WE and the physical wobble signal. On the other side, due to the crosstalk cannot interfere the land pre-pit signal, the phase of the synthesized wobble signal WS is calibrated by the land pre-pit signal. In conclusion, the present invention provide a synthesized wobble signal synchronized with the rotation speed of the optical disc, therefore the synthesized wobble signal is suitable to be reference as a recording clock or other applications.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method 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.
Patent Application
20070086286
