Abstract:
A method for discriminating an optical disk is disclosed. Peak values and trough values of focus error signal and RF level signal are detected by an operation of focus search. Threshold levels for detecting each material layer of the optical disk are determined according to the peak values and the trough values. Thereafter another focus search for the optical disk is executed to calculate a thickness of the substrate and a distance between the first and the second recording layer of the optical disk according to the threshold levels. Thus the type of the optical disk can be discriminated.

Description:
BACKGROUND OF INVENTION  
   1. Field of the Invention 
   The present invention relates to a disk discrimination method, and more specifically, to a stable disk discrimination method. 
   2. Description of the Prior Art 
   There are many kinds of optical disks, such as CD-ROM, CD-R, CD-RW, Hybrid CD, single-layer DVD, double-layer DVD, DVD-R, DVD+R, DVD-RW, DVD+RW, DVD-RAM, and so on. Because different kinds of optical disks have different data formats and different physical characters, an optical disk drive includes several data-reading methods, like exchanging wavelengths of the laser beams emitted from a pick-up head (CD: 780 nm, DVD: 650 nm) or amplifying some predetermined signals. Therefore, when the optical disk is loaded into the optical disk drive capable of reading various kinds of optical disks, the optical disk needs to be discriminated for determining the next data-reading step corresponding to the optical disk. 
   Please refer to  FIG. 1 .  FIG. 1  is a diagram of a focus mechanism with a pick-up head of an optical disk drive. A laser diode  1  is used for generating a laser beam, and the laser beam generated by the laser diode  1  is passed through a beam splitter  3  and an object lens  5  to generate a focus point  9 . A focus actuator  11  can actuate the object lens  5  to move upward or downward so as to change the location of the focus point  9 . The light reflected from the focus point  9  on an optical disk  7  is emitted to a photo detector  13  via the beam splitter  3 . The photo detector  13  can generate optical signals, such as focus error signal, RF signal, RF level signal, sub-beam add signal, and so on, for controlling focus of the laser beam. 
   There are two control methods for controlling the focus actuator  11 . One is an open-loop control method, and the other is a close-loop control method. The disk discrimination is relative to the open-loop control method, and the detailed introduction is described as follows. 
   Please refer to  FIG. 2 .  FIG. 2  is a control functional block diagram of the focus open-loop control method. A host sends a control command to a digital/analog IC  20 , and then the digital/analog IC  20  generates a control signal. The control signal can be amplified by a driving IC  22  into a focus-driving signal to drive a focus actuator  24  so that the focus point can move upward (as a direction  19  shown in  FIG. 1 ). At the same time, a photo detector  26  can generate a signal and transmit the signal to an RF amplifier  28  for generating a focus error signal. The distances between each material layers are determined according to the focus error signal. 
   An optical disk with a single recording layer structure is shown as the optical disk  7  in the  FIG. 1 . When the pick-up head reads/writes data from the optical disk, the laser beam will reach a reflective layer  15 , the material layer for recording data, via a plastic layer  17 . The thickness of the plastic layer  17  of a DVD-format optical disk is 0.6 mm while CD-format optical disk is 1.2 mm. Therefore the optical disk can be discriminated whether it is DVD format or CD format according to the distance from the surface of the plastic layer  17  to the reflective layer  15  (i.e. the thickness of the plastic layer  17 ). 
   The conventional method for discriminating optical disks is by means of the focus error signal. Please refer to  FIG. 3 .  FIG. 3  is a diagram illustrating a S-curve of the focus error signal and the RF level signal in the prior art. The focus point  9  is approaching a Hybrid CD  38  in a direction  56 . The S-curve can be plotted by tracking the focus error signal. When the distance between the focus point  9  and the Hybrid CD  38  approaches infinity, the reflective light is slight so that the focus error signal is also slight. When the focus point  9  is approaching a first reflective layer  42  of the Hybrid CD  38 , the focus error signal increases to a positive peak value FE_PK 1 . And when the focus point  9  reaches the first reflective layer  42 , the focus error signal decreases to a zero intersection  52 . Afterward the focus point  9  is away from the first reflective layer  42 , the focus error signal decreases to a negative trough value FE_BT 1  and then increases to the zero to form a S-curve. 
   As shown in  FIG. 3 , when the focus point  9  passes through three material layers, a plastic layer  40 , the first reflective layer  42 , and a second reflective layer  44 , the focus error signal includes the S-curves S 0 , S 1 , and S 2 . The distances between the zero intersections  50 ,  52 ,  54  of the S-curves S 0 , S 1 , S 2  are the distances between the material layers. 
   The optical disks are discriminated according to the distances between the zero intersections of the S-curves in the prior art. However the amplitude of the S-curve of the plastic layer is not so obvious as the ones of the first reflective layer  42  and the second reflective layer  44 . Sometimes it is difficult to detect the distance between the plastic layer  40  and the first reflective layer  42 , so it is also difficult to discriminate the format of the optical disk. Therefore there is a need to discriminate the format of the optical disk more efficiently. 
   SUMMARY OF INVENTION  
   It is therefore a primary objective of the present invention to provide a disk discrimination method to solve the problem mentioned above. 
   Briefly summarized, a method for discriminating an optical disk is disclosed. Amplitude of focus error signal and RF level signal are detected by an operation of focus search. Threshold levels for detecting each material layer of the optical disk are determined based on the amplitude of the focus error signal and RF level signal. Thereafter another focus search for the optical disk is executed to calculate a thickness of the substrate and a distance between the first and the second recording layer of the optical disk according to the threshold levels. Thus the type of the optical disk can be discriminated. 
   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 DRAWINGS  
       FIG. 1  is a diagram of a focus mechanism in an optical disk drive. 
       FIG. 2  is a control functional block diagram of the focus open-loop control method. 
       FIG. 3  is a diagram illustrating a S-curve of the focus error signal and the RF level signal in the prior art. 
       FIG. 4  is a flowchart of the disk discrimination according to the present invention. 
       FIG. 5  is a diagram illustrating the threshold levels derived from the peaks and troughs of the signals in step  100  of the flowchart shown in  FIG. 4 . 
       FIG. 6  is a detailed flowchart of the step  120  of the flowchart shown in  FIG. 4 . 
       FIG. 7  is a comparative diagram illustrating the signals of a CD and a single-layer DVD. 
       FIG. 8  is a comparative diagram illustrating the signals of a Hybrid CD and a double-layer DVD. 
   

   DETAILED DESCRIPTION  
   The present invention utilizes a focus open-loop control method to detect the structure of an optical disk so as to discriminate the format of the optical disk. Please refer to  FIG. 4 .  FIG. 4  is a flowchart of the disk discrimination according to the present invention. The method includes the following steps: 
   Step  100 : Operate a first focus search for the optical disk. 
   Step  110 : Determine threshold levels of a focus error signal and a RF level signal for detecting each material layer of the optical disk. 
   Step  120 : Operate a second focus search for detecting the distances between the material layers of the optical disk so as to discriminate the format of the optical disk. 
   In step  100 , an object lens can be moved upward and downward in the focus open-loop control method to operate the first focus search for the optical disk. For example, as shown in  FIG. 3 , when a focus point passes through a Hybrid CD which consists the plastic layer  40 , the first reflective layer  42  (recording layer) and the second reflective layer  44  (recording layer), there are peaks (RFL_PK 0 , RFL_PK 1 , RFL_PK 2 ) in the RF level signal while there are S-curves (S 0 , S 1 , S 2 ) in the focus error signal. The peaks and troughs of the above mentioned signals can be detected by a peak detector. Thereafter the threshold levels in step  110  can be acquired based on the detected peaks and troughs. 
   In step  110 , the threshold levels of the focus error signal and the RF level signal for detecting each material layer of the optical disk can be determined. This step is executed for calculating the distances between the material layers of the optical disk in step  120  more precisely 
   Please refer to  FIG. 5 .  FIG. 5  is a diagram illustrating the threshold levels (THa, THb, THc, TH 1 , TH 2 , TH 3 , TH 4 ) derived from the peaks and troughs of the signals in step  100 . The computation of the threshold levels is as follows: 
   THa and THb are the threshold levels of the RF level signal corresponding to the situation in which the focus point passes through the plastic layer  40 .
 
 Tha=RFL   —   PK 0* Ra  ( Ra&lt; 1);
 
 THb=RFL   —   PK 0* Rb  ( Rb&lt; 1); and  Ra≠Rb 
 
   THc is the threshold level of the RF level signal corresponding to the situation in which the focus point approaches the first reflective layer  42 .
 
 THc=RFL   —   PK 1* Rc  ( Rc&lt; 1);
 
   TH 1  and TH 2  are the threshold levels of the focus error signal in a half wave of the S-curve corresponding to the situation in which the focus point approaches the first reflective layer  42 . Generally a positive peak of the S-curve is not necessarily symmetric to a negative through of the S-curve. That is, the absolute value of FE_PK 1  is not necessarily equal to the absolute value of FE_BT 1 . For the accuracy of the measure, the greater half wave of the S-curve would be selected for determining the threshold level of the focus error signal.
 
 IF |FE   —   PK 1|&gt;| FE   —   BT 1|
 
 TH 1= FE   —   PK 1* R 1 ( R 1&lt;1);
 
 TH 2= FE   —   PK 1* R 2 ( R 2&lt;1); and  R 1≠ R 2
 
 IF |FE   —   PK 1|&lt;| FE   —   BT 1|
 
 TH 1= FE   —   BT 1* R 1 ( R 1&lt;1);
 
 TH 2= FE   —   BT 1* R 2 ( R 2&lt;1); and  R 1≠ R 2
 
   IF |FE_PK 1 |=|FE_BT 1 |, TH 1  and TH 2  can be derived from either of the above methods. 
   TH 3  and TH 4  are the threshold levels of the focus error signal in a half wave of the S-curve corresponding to the situation in which the focus point approaches the second reflective layer  44 . The method for generating TH 3  and TH 4  is similar to the method for generating TH 1  and TH 2 . That is, the greater half wave of the S-curve would be selected for determining the threshold level of the focus error signal. 
   The threshold level mentioned above is derived from the product of the peak of the signal or the trough of the signal and a ratio, and the ratio is less than 1 and is derived from a previous experiment. 
   After determining the threshold levels of the RF level signal and the focus error signal for detecting material layers of the optical disk in step  110 , the second focus search in step  120  is executed. Please refer to  FIG. 6 .  FIG. 6  is a detailed flowchart of the step  120 .  FIG. 6  illustrates the flowchart for detecting the format of the optical disk when the positive peak of the S-curve is greater than the negative trough of the S-curve. 
   Step  200 : Detect the RF level signal, and when the RF level signal is greater than THa and then is less than THb, switch on a counter A. 
   Step  210 : When the RF level signal is greater than THc, detect the focus error signal instead. 
   Step  220 : When the focus error signal is greater than TH 1  and then is less than TH 2 , switch off the counter A and switch on a counter B. 
   Step  230 : If the focus error signal is greater than TH 3 , go to step  240 ; if not, end the process. 
   Step  240 : If the focus error signal is less than TH 4 , switch off the counter B. 
   Please refer to  FIG. 5 . When the second focus search is executed, the RF level signal is detected first. When the focus point is approaching the surface of the plastic layer  40 , the RF level signal is becoming greater. When the RF level signal is greater than the threshold level of the RF level signal THa, it means the plastic layer  40  exists, and the system continues detecting the RF level signal. When the RF level signal is less than the threshold level of the RF level signal THb, the focus point is passing through the surface of the plastic layer  40  and the system switches on the counter A, as shown in step  200 . And then the system continues detecting the RF level signal. When the RF level signal is greater than the threshold level of the RF level signal THc, the focus point approaches the first reflective layer  42  and the system detect the focus error signal instead, as shown in step  210 . 
   If the focus point approaches the first reflective layer  42  even more, the focus error signal becomes greater. When the focus error signal meets the threshold level of the focus error signal TH 1 , the focus point is near the first reflective layer  42 . When the focus error signal meets the threshold level of the focus error signal TH 2 , the focus point reaches the first reflective layer  42 . At the same time, the counter A stops counting, and a count value generated by the counter A, countA, corresponds to the distance between the plastic layer  40  and the first reflective layer  42 , as shown in step  220 . 
   When the counter A stops counting, the system switches on the counter B and then continues detecting the focus error signal. If the optical disk is a double-recording-layer optical disk, the S-curve of the second reflective layer  44  exists. And if the optical disk is a single-recording-layer optical disk, the S-curve of the second reflective layer  44  does not exist. So if the focus error signal is less than the threshold level of the focus error signal TH 3  during a predetermined period, the optical disk is the single-recording-layer optical disk. And then the counter B stops counting to end the process, and the count value generated by the counter B is useless (step  230 ). 
   On the contrary, when the focus point approaches the second reflective layer  44 , the focus error signal becomes greater. When the focus error signal meets the threshold level of the focus error signal TH 3 , the focus point is near the second reflective layer  44 . When the focus error signal meets the threshold level of the focus error signal TH 4 , the focus point is reaching the second reflective layer  44 . At the same time, the counter B stops counting, and a count value generated by the counter B, countB, corresponds to the distance between the first reflective layer  42  and the second reflective layer  44 , as shown in step  240 . 
   The format of the optical disk can be discriminated by step  120  (steps  200 – 240 ). According to the distances calculated by the counter A and the counter B, the distances between the material layers of the optical disk can be derived so as to discriminate the format of the optical disk. 
   Please refer to  FIG. 7 .  FIG. 7  is a comparative diagram illustrating the signals of a CD and a single-layer DVD. The countA of the CD is much greater than the countA of the single-layer DVD because the thickness of the plastic layer of the CD is greater than the thickness of the plastic layer of the single-layer DVD. Hence the format of the optical disk can be discriminated to be the CD or the single-layer DVD according to the countA. 
     FIG. 8  is a comparative diagram illustrating the signals of a Hybrid CD and a double-layer DVD. If the focus error signal meets the threshold level of the focus error signal TH 3 , the optical disk is a double-layer disk. The countB of the Hybrid CD is much greater than the countB of the double-layer DVD because the distance between the second reflective layer and the first reflective layer of the Hybrid CD is greater than the distance between the second reflective layer and the first reflective layer of the double-layer DVD. Hence the format of the optical disk can be discriminated to be the Hybrid CD or the double-layer DVD according to the countB. 
   The present invention is not limited to the single-layer and the double-layer optical disks. The multiple-layer optical disks also can be discriminated according to the present invention in a similar way. In addition, a sub-beam add signal can be substituted for the RF level signal of the above-mentioned embodiment to make the same effect. 
   In contrast to the prior art, the advantage of the present invention is detecting the optical disk more stably and precisely. It is because a first focus search is utilized for determining the thresholds of the material layers, and a second focus search is utilized for detecting the distances between the material layers of the optical disk so as to discriminate the format of the optical disk completely and accurately instead of utilizing constant thresholds of the signals in the prior art. 
   The other advantage of the present invention is to improve the problem that the S-curve of the plastic layer is unobvious when detecting the S-curve in the prior art. That is, the RF level signal substitutes for the S-curve to detect the plastic layer, and then the format of the optical disk can be discriminated from the S-curve according to the thickness of the plastic layer and the distances between the material layers in the present invention. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the 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.