Abstract:
The present invention relates to an apparatus and method for analyzing the read-out signal of an optical storage media and is especially suitable for the HF signal read from the digital video disk (DVD), wherein the HF signal comprises many different signals whose periods are integer times of the system period. The present apparatus can be used to record the maximum or minimum values of specific period of signals for further statistical analyses. Furthermore, the AC and DC components of the HF signal can be processed independently and the results will be combined together for further processes. Therefore, it only takes moderate memory capacity and acquisition time to obtain accurate maximum or minimum values of the specific period of signals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an apparatus and method for analyzing the read-out signal of an optical storage media and is especially suitable for the HF signal read from the digital video disk (DVD), wherein the HF signal comprises many different signals whose periods are integer times of the system period. The present apparatus and method can be used to record the maximum and minimum values of specific period of signals for further statistical analyses. 
     2. Related Art 
     The read-out signal of the DVD disk includes a series of different signals whose periods are integer times of the system period and is also called the HF signal. The period of the shortest signal is three times of the system period T, referred to the 3T-signal, while that of the longest signal is fourteen times of the system period, referred to the 14T-signal. The statistical analyses of the maximum and minimum values of specific period of signals have become important factors for verifying the disk quality. 
     One conventional way for obtaining the maximum and minimum values of a signal is to use a digital storage scope for recording the signal and then analyze the recorded signal by using some special programs. But because the method mentioned above needs a great number of memories to store all the information included in the signal regardless of its being useful or not, it is only suitable for low frequency signal with a short duration of time. Therefore, due to the limited memory capacity in a digital storage scope, it is impossible to obtain enough maximum and minimum values of the 3T-signal for further statistical analyses. Consequently, such a method is not suitable for analyzing the HF signal read from the DVD disks. 
     SUMMARY OF THE INVENTION 
     The present invention discloses an apparatus and method for analyzing the read-out signal of an optical storage media, by which the high frequency (HF) signal read from the optical storage media and the eight to fourteen modulation (EFM+) signal sliced from the HF signal can be processed to obtain the DC component signal via a low-pass filter. The HF signal and the DC component signal will then be fed to a differential amplifier to obtain the AC component signal of the HF signal. The present apparatus also includes a first switch unit for choosing whether the maximum value or the minimum value will be measured. Moreover, a 3T-signal detector unit and an nT-signal detector unit will be used to detect whether the positive edge, or the negative edge, of the current EFM+ signal occurs during the time interval of detection. A second switch unit is also included to choose between the 3T-signal detector unit and the nT-signal detector unit. Finally, the period of the current EFM+ signal will be identified and the HF signal may be recorded according to the identification result for further verifications. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow by illustration only, and thus is not limitative of the present invention, and wherein: 
     FIG. 1A discloses a timing flowchart of the method for analyzing the read-out signal of a DVD disk according to the present invention; 
     FIG. 1B discloses a signal flowchart of the method for analyzing the read-out signal of a DVD disk according to the present invention; 
     FIG. 2 discloses a block diagram of the apparatus for analyzing the read-out signal of a DVD disk according to the present invention; 
     FIG. 3 discloses a timing diagram of the apparatus for analyzing the read-out signal of a DVD disk according to the present invention; 
     FIG. 4 shows a circuit schematic of the 3T-signal detector unit according to the present invention; and 
     FIG. 5 shows a circuit schematic of the nT-signal detector unit according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the read-out signal of an optical storage media, such as a DVD disk, includes a series of different signals whose periods are integer times of the system period and is also called the HF signal. The present invention proposes an apparatus and method for analyzing the modulation signal and the asymmetry signal in the HF signal. The apparatus is used to record the maximum and minimum values of specific period of signals from the HF signal so as to verify the quality of DVD disks. The HF signal and the EFM+ signal sliced from the HF signal used for the present invention can be easily obtained from the circuit of a commonly used DVD drive. 
     The timing flowchart of the method for analyzing the read-out signal of a DVD disk according to the present invention is shown in FIG.  1 A. The HF# signal and the EFM+ signal are first fed to an analog to digital converter (ADC), as shown in step  100 , to obtain the maximum and minimum values of the HF# signal, as shown in step  102 , and to identify whether the current EFM+ signal is a nT-signal, as shown in step  104 . Since the EFM+ signal is sliced from the HF# signal, it will lag the HF# signal for a short time. Therefore, when the identification of the current EFM+ signal is completed, it may be too: late to catch the maximum or minimum signal of the HF# signal on time. To overcome the problem mentioned above, we could catch the maximum or minimum signal of the HF# signal in advance and latch it in a D-type flip-flop. If the current EFM+ signal is ascertained to be a nT-signal, then the data latched in the D-type flip-flop will be stored into a static random access memory unit, as shown in step  106 , and output to a central processor unit; if not, the data will be discarded, as shown in step  108 . 
     The signal flowchart of the method for analyzing the read-out signal of a DVD disk according to the present invention is shown in FIG.  1 B. The first step is to provide the HF# signal, which comprises both the DC and AC component signals and is shown in step  200 , to a non-inverting amplifier, as shown in step  202 , and an inverting amplifier, as shown in step  204 , simultaneously for signal amplification. And a switch is also provided to choose whether the maximum value or the minimum value will be measured. Moreover, The HF# signal is also fed to a low-pass filter for obtaining the DC component, as shown in step  208 . The amplified signals and the DC component of the HF# signal will then be fed to an analog to digital converter. (ADC) and a D-type flip-flop respectively, as shown in steps  210  and  212 . Finally, the processed data may be discarded or stored in a static random access memory unit, as shown in steps  214  and  216 , and subsequently output to a central processor unit. Furthermore, the EFM+ signal, as shown in step  218 , is also fed respectively to a 3T-signal detector, as shown in step  220 , and a nT-signal detector, as shown in step  222 , for identifying different period of signals. By using a switch, as shown in step  224 , the user can choose which result of the above two detectors will be used to control whether the data latched in the D-type flip-flop will be stored into the static random access memory unit, as shown in steps  214  and  216 . 
     The block diagram of the apparatus for analyzing the read-out signal of a DVD disk according to the present invention is shown in FIG. 2, and the detailed description of each block will be given below in cooperation with the timing diagram as shown in FIG.  3 . 
     First of all, the HF# signal is fed to a low-pass filter unit  10  to produce a DC component signal with a little amount of ripple, AVG#. The AVG# signal and the HF# signal are then fed to a non-inverting differential amplifier unit  12  for amplifying the AC component of the HF# signal while reserving the DC component so as to obtain the PK# signal. Subsequently, the PK# signal will go through a first switch unit  16  and be fed to a high-speed hysteresis comparator unit  18 , such as AD8561, with the AVG# signal together. When the amplitude of the PK# signal is below the value of a or above the value of b, the comparator unit  18  will change its output state and thus produce the ENC# signal. The ENC# signal will then be used to trigger the analog to digital converter units  22  and  26  to sample and convert signals. The ENC# signal can also be fed to the delayed pulse generator unit  24  so as to produce the LOCK# signal and the discharging signal, DISC#. The LOCK# signal is used to trigger the D-type flip-flops  28  and  30  to latch the output of the analog.to digital converter units  22  and  26 . Because the DISC# signal can be used to discharge the capacitor in the peak detector unit  20 , therefore, the DISC# signal and the PK# signal from the switch  16  will be fed to the peak detector unit  20  for producing the PKD# signal. 
     Subsequently, the AVG# signal and the ENC# signal are both fed to the high-speed analog to digital converter unit  22 , such as AD9283BRS-100, so as to digitize the AVG# signal into the XAVG# signal in 10 ns after t 1 . Similarly, the PKD# signal and the ENC# signal are also be fed to the high-speed analog to digital converter unit  26  to digitize the PKD# signal into the XPKD# signal in 10 ns after t 1 . At t 1 +Δt 1 , the state of the LOCK# signal is positive edge and thus will trigger the D-type flip-flop unit  28  to latch the XAVG# signal and subsequently output to the buffer unit  32 . Meanwhile, the D-type flip-flop unit  30  will also latch the XPKD# signal and subsequently output to the buffer unit  34 . Therefore, with reference to FIG. 2, during two successive peaks of the HF# signal, both of the AVG# and PKD# signals will be digitized and latched in the D-type flip-flop units  28  and  30 , respectively. 
     If the user wants to record the peak value of a specific signal in the HF# signal whose period is integer times of the system period, then the XAVG# and XPKD# signals, previously latched in the D-type flip-flop units  28  and  30  respectively, should be immediately stored into the static random access memory units  36  and  38  via the buffer units  32  and  34  respectively as soon as the specific period of signal is successfully identified. When the acquisition time is reached, all the peak values stored in the static random access memory units  36  and  38  can be fetched by the central processor unit  40  via the parallel input/output interface unit  42  for further statistical analyses. 
     If the gain of the non-inverting amplifier unit  12  is A, then the relation between the HF# and the PK# signals can be described as follows. 
     
       
         PK=A *(HF−AVG)+AVG 
       
     
     Since the value obtained from the peak .detector unit  20  is the peak value of the PK# signal, not that of the HF# signal, therefore the actual peak value of the HF# signal, PEAK#, can be easily expressed in terms of the AC component signal, XPKD# - XAVG#, and the DC component signal, XAVG, as follows. 
     
       
         PEAK=K * ((XPKD−XAVG)/A+XAVG), wherein K is a constant coefficient. 
       
     
     In general, the DVD drive can be used to slice the HF# signal so as to obtain the EFM+ signal by way of shaping the HF# signal as a series of rectangular waveforms. Therefore, the EFM+ signal will lag the HF# signal for t 2 -t 0 . 
     The EFM+ signal can be fed to the 3T-signal detector unit  44  via the switch unit  16 , wherein the 3T-signal detector unit  44  can be used to identify whether the current EFM+ signal is a 3T-signal or not. If the current EFM+ is ascertained to be a 3T-signal; then the 3T-signal detector will produce a write signal, WR3T#, after Δt 4  of delay when the negative edge of the 3T-signal occurs. The WR3T# signal can then be used to trigger the static random access memory units  36  and  38  to store the values of XAVG# and XPKD# signals, which are previously latched in the D-type flip-flop units  28  and  29 , via the buffer units  32  and  34 , respectively. 
     FIG. 4 shows the circuit schematic of the 3T-signal detector unit  44 . At t 2 , the positive edge of the EFM+ signal will trigger the first one-shot multivibrator  52  to produce a pulse signal, M3T, with time period of 2.5T. Subsequently, the M3T signal will trigger the second one-shot multivibrator  54  to produce a pulse signal with time period of 1T, which will be fed to the first JK flip-flop  56 . At t 5 , the negative edge of the EFM+ signal will also trigger the first JK flip-flop  56  and produce at t 5 +Δ 4  a pulse signal, WR3T#. The time delay of Δt 4  is due to the internal delay of the first JK flip-flop circuit  56 . 
     If the user wants to record the XAVG# and XPKD# signals of the HF# signal with nT periods of time, then the EFM+ signal should be fed to the nT-signal detector  46  via the switch unit  16 . The nT-signal detector unit  46  can be used to identify whether the current EFM+ signal is a nT-signal or not. If the current EFM+ is ascertained to be a nT-signal, the nT-signal detector will produce a write signal, WRnT#, after Δt 4  of delay when the negative edge of the vT-signal occurs. By switching the second switch unit  48  to an appropriate position, the WRnT# signal can then be used to trigger the static random access memory units  36  and  38  to store the values of XAVG# and XPKD# signals, which are previously latched in the D-type flip-flop units  28  and. 30 , via the buffer units  32  and,  34 , respectively. The waveform of the WRnT# signal output from the nT-signal detector unit  46  when n=6 is shown in FIG.  3 . 
     FIG. 5 shows the circuit schematic of the nT-signal detector unit  46 . At tx, the positive edge of the EFM+ signal will trigger the three one-shot multivibrator  58  in the 3T-signal detector unit  46  to produce a pulse signal, M3T, with time period of 2.5T. The M3T signal will then be fed to the XOR gate  60 . Meanwhile, the positive edge of the EFM+ signal will also trigger the fourth one-shot multivibrator  62  to produce a pulse signal with time period of (n−0.5)T to the- XOR gate  60 , wherein the value of n can be adjusted by VR 1  and later another pulse signal with time period of 1T is produced to be fed to the 2J input terminal of the second JK flip-flop  64 . If the negative edge of the EFM+ signal triggers the second JK flip-flop  64  at ty and ty-tx&lt;(n−0.5T), then the second JK flip-flop  64  will send a clear signal, CLR# which is not shown on the drawing, to the third one-shot multivibrator  58  and the fourth one-shot multivibrator  62  so that the WRnT# will not be produced. The WRnT# signal will be produced only if ty-tx=nT. 
     As shown in FIG. 3, the positive edge of the EFM+ signal triggers the third one-shot multivibrator  58  and the fourth one-shot multivibrator  62  at t 2  and clears them at t 5 . Similarly, the positive edge of the EFM+ signal triggers the third one-shot multivibrator  58  and the fourth one-shot multivibrator  62  again at t 6  and also clears them at t 8 . But when the positive edge of the EFM+ signal triggers the third one-shot multivibrator  58  and the fourth one-shot multivibrator  62  at t 10 , the WRNT# signal will be produced at t 12 +Δt 4  because t 12 −t 10 =nT. 
     One more embodiment of the present invention is to record the minimum value of a specific signal in the HF# signal whose period is integer times of the system period. The method for obtaining the minimum value of the HF# signal is similar to the previous method. That is, both of the AVG# and HF# signals are fed to the inverting differential amplifier unit  14  for amplifying the AC component of the HF# signal while reserving the DC component so as to obtain the NPK# signal. The IEFM+ signal can also be obtained by feeding the EFM+ signal to an inverter. With reference to FIG. 3, only by switching the states of S 1  and S 2  in the switch  16 , all the processes for obtaining the minimum value of the HF# signal are the same as that for obtaining the maximum value. But the equation for calculating the minimum value of the HF# signal, VPEAK#, should be modified as follows. 
     
       
         VPEAK=K * (XAVG−(XPKD−XAVG)/A) 
       
     
     Wherein K is a constant coefficient and the gain of the inverting amplifier unit  14  is supposed to be the same as that of the non-inverting amplifier unit  12 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.