Disk discrimination apparatus for an optical disk reproducing apparatus

Abstract: A disk discrimination apparatus for use in an optical disk reproducing apparatus detects a tracking error signal (TE) to discriminate between disks, and prevents reproduction of a disk which does not correspond to the reproducing apparatus. In the disk discrimination apparatus, when a second type disk (DVD) having a track pitch which is smaller than that of a first type disk (CD) is played by the optical disk reproducing apparatus, a discriminator (105) detects that the disk is not a first type disk (CD) based on an output signal of a tracking error signal generating circuit (103). The discriminator (105) performs a discrimination operation by comparing the signal level of a signal passed through the tracking error signal generating circuit with a predetermined reference value. In another embodiment, the discriminator (105) includes a counter for counting the number of zero-crossings (TZC) of the signal passed through the tracking error signal generating circuit, and performs the disk discrimination using a count value of the counter. In a further embodiment, when the second type disk is played by the optical disk reproducing apparatus, the discriminator detects that the disk is not a first type disk based on an output signal of a focus sum signal (FSUM).

Description: The present invention relates to a disk discrimination apparatus according to the preamble of claim 1. US-A-4 773 052 discloses such a disk discrimination apparatus for use in an optical disk reproducing apparatus, wherein a discriminator is provided that distinguishes between video and digital audio disks having different signal recording formats. The difference is detected in such factors as the thickness of each disk, the diameter across the disk, its mass, reflectance and the recorded or reproduced signal. EP-A-0 790 604 discloses a reproduction device for optical disks, wherein signal processing systems can be switched according to the optical system selected from a plurality of optical systems and set to the operating state. A system controlling portion finally sets an appropriate optical system according to the kind of an optical disk and sets an appropriate signal processing system corresponding to the set optical system for setting an appropriate mode depending upon CD or DVD. EP-A-0 767 455 discloses an optical record medium judging method and apparatus, wherein a servo controller calculates on the basis of a focus error signal a peak value thereof and the disk is judged on another basis of the peak value of the focus error signal as detected. Among conventional disk reproducing apparatuses, discrimination of disk types is typically performed between CD (Compact Disc) and LD (Laser Disc). The discrimination between CD and LD is possible by using different diameters of the CD and LD. More specifically, the pickup is firstly moved at a position outside the area of CD and inside the area of LD, the loaded optical disk is then rotated, and determination is made as to whether or not the focus servo system locks. If it locks, the loaded disk is determined as LD, and if it does not locks, the disk is determined as CD. On the other hand, in recent years there exists a strong demand for the increase of the recording capacity, and broadening of the compatibility among devices are also required. To meet these demands, disks of the same size having different recording formats, such as DVD (Digital Versatile Disk, or Digital Video Disk) are being developed. DVD has the same diameter as CD, and its recording capacity is more than 4 gigabytes which is by far greater than 640 megabytes of the CD's recording capacity. The pit size and track pitch of DVD are smaller than those of CD, so that information is recorded at high density. When it is attempted to reproduce a DVD by a player for CD reproduction, the reproduction of DVD having high recording density is not possible because the diameter of the beam spot of the pickup is too large to read the pits on the DVD. Furthermore, locking of the focus servo system is also tried when reproducing a DVD, that operation however may cause a loss of control of the pickup moving mechanism because the tracking error signal is nor properly produced when closing of the tracking servo system is attempted. An object of the present invention is therefore to provide an apparatus for discriminating disks, to prevent the reproduction of a disk which does not correspond to the player. The discrimination is made, for example, by using a tracking error signal obtained when the tracking servo loop is open, and the apparatus prevents, for example, the reproduction of DVD in a CD player. This object is achieved by the features in the characterizing part of claim 1. The disk discrimination apparatus according to the invention performs the discrimination of disks, thereby allowing the discrimination between different optical disks, such as CD and DVD, by using the arrangement of a simple structure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing a basic structure of the embodiments of the optical disk reproducing apparatus according to the present invention; Fig. 2 is a diagram showing a part of the circuit of the first embodiment of the present invention; Fig. 3 is a diagram showing a part of the circuit of the second embodiment of the present invention; Figs. 4A and 4B are diagrams showing signals appearing in the embodiment of the present invention; Fig. 5 is a flowchart showing the operation of the first embodiment of the present invention; and Fig. 6 is a flowchart showing the operation of the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the disk discriminating apparatus according to the present invention will be described with reference to the accompanying drawings. In the embodiments of the present invention, the light receiving system and the manner of generation of the information reading signal and the tracking error signal are basically the same as those employed in CD players. Fig. 1 is a block diagram showing the structure of an embodiment of the disc type discrimination apparatus according to the present invention. In Fig. 1, the pickup 101 emits reading light to a disk (not illustrated) and receives a reflection light to supply an electrical signal corresponding to the light amount of the reflection light to a tracking error (TE) generation circuit 103 and an LPF (Low Pass Filter) 107. The TE generation circuit 103 generates a tracking error signal TE, and supplies it to a tracking zero crossing (TZC) generation circuit 104. The tracking error signal TE is a signal that primarily contains an error component of an irradiation position of the reading beam relative to a recording track center of the disk. In the TZC generation circuit 104, a signal whose polarity inverts at each zero-crossing of the tracking error signal is produced, and the signal is supplied, as a zero-crossing signal, to a microprocessor 105. The readout information signal (hereinafter, referred to as radio frequency signal RF) supplied to the LPF 107, is processed by the LPF 107 so that its high-frequency components are eliminated, and its a low-frequency component only is extracted. The low frequency component extracted at the LPF 107 is supplied to focus sum signal (FSUM) generation circuit 108. In the FSUM generation circuit 108, a focus sum signal is generated, and the signal is then supplied to a focus sum signal zero-crossing (FSUMZC) generating circuit 109. In the FSUMZC circuit 109, a signal whose polarity inverts at each zero-crossing of the focus sum signal is generated, and the signal is supplied, as a focus sum zero-crossing signal, to the microprocessor 105. In the microprocessor 105, counting of the number of zero-crossings of each of the supplied zero-crossing signals is performed, and a count number comparing process in which the counted values are compared with values stored in ROM (not illustrated) previously. The tracking servo control circit (IC) 106 receives a tracking control instruction from the microprocessor 105, and drives a tracking drive coil of a pickup 101 by a tracking drive signal produced by a signal processing of the tracking error signal, thereby constitutes a tracking servo system. A disk discrimination process is performed by using results of the count number comparing process at the microprocessor 105. An example of the TZC generation circuit 104 will be explained by way of an example in which a hysteresis comparator (a comparator having a hysteresis characteristic) is employed as shown in Fig. 2. In Fig. 2, the tracking error signal is supplied to an input terminal 202 of the comparison processing circuit, and an output signal of a result of comparison at a comparator 201 is obtained at an output terminal 203. The tracking error signal received at an input terminal 202 is filtered by a low-pass filter which is constituted by a resistor R5 and a capacitor C2, and an AC component of a low-frequency component of the tracking error signal flows through a capacitor C1, and superposed on a reference voltage Vref. The signal produced by the superposition is compared at the comparator 201, which has a hysteresis characteristic produced by a feedfoward through a resistor R4, with the reference voltage Vref at a minus terminal of the comparator 201, and a result of the comparison is given out as a square wave at the output terminal 203. An example of a comparator without the hysteresis characteristic and without the provision of the low-pass filter will be explained with reference to Fig. 3. The tracking error TE is received at an input terminal 302 of a comparison processing circuit, and a result of the comparison by a comparator 301 is provided at an output terminal 303. An ac component of the tracking error signal received at the input terminal 302 passes through the capacitor C1, and superposed on the reference voltage Vref. The signal produced by the superposition is compared with the reference voltage Vref at the minus input terminal of the comparator 301, and a result of the comparison is given out as a square wave at the output terminal 303. In this example, a resister of a large resistance value is used as the resistor R4 so that a hysteresis characteristic is not produced. Waveforms of various signals obtained by the player having the above-described configuration, when performing the reproduction with a CD being loaded and the reproduction with a DVD being loaded, are depicted in Figs. 4A and 4B respectively. When a CD is loaded in a CD player and a reproduction operation is performed, a tracking error signal TE, an RF signal RF, and a low frequency component FSUM of the focus sum signal are produced as illustrated in Fig. 4A when the tracking servo loop is open, that is, in a period after locking of the focus servo loop and before closing of the tracking servo loop. When a disk of high density recording, such as a DVD, is loaded and the reproduction operation is performed, the above-described signals will not be generated accurately, as depicted in Fig. 4B. In Figs. 4A and 4B, the waveform illustrated as the S-curve signal is a focus error signal produced by a focus error generation circuit (not illustrated in Fig. 1). The sign TE represent an output signal produced by the TE generating circuit 103 of Fig. 1, and RF represents an output signal of the LPF 107 of the circuitry shown in Fig. 1. The sign FSUM represents an output signal of the FSUM generating circuit 108, and the numerals 203 and 303 represent output signals of the TZC generating circuit 104 shown in Fig. 1. The pickup for CD has a modulation transfer function (MTF) characteristic which allows an optimum reading for spacial frequency components carried by a CD (spacial frequency components of a train of pits recorded on a CD). Therefore, if an optical disk on which a high density recording is performed such as a DVD is reproduced by the pickup for CD, the signal level of the reproduction signal will be lowered because of such a reason that the spacial frequency components of the high density recorded optical disk fall outside the bandwidth given by the MTF characteristic of the pickup for CD. Consequently, if it is attempted to reproduce a high density recording disk such as DVD with a pickup for CD, the signal level of the RF signal RF becomes extremely lower than that obtained when reproducing a CD. This leads to a result that both of the tracking error signal TE, the low frequency component FSUM of the focus summation signal become lower than the signal level of the error signal obtained with a CD, and assume output signal waveforms as illustrated in Fig. 4B. Now, the first embodiment of the present invention will be explained with reference to Fig. 1 and the flowchart of Fig. 5. The flowchart of Fig. 5 shows the counting and comparison process performed by using the circuitry shown in Fig. 2 which includes a hysteresis comparator. As depicted in the flowchart, the focus servo is turned on at step S1, and the disk is rotated at step S2. The rotational speed is, for example, 600 r.p.m. Then, the number of tracking zero-crossings TZC is measured at step S3, and detection is made at step S4 as to whether the measured TZC is smaller than a comparison reference TZCa which has been set previously. If TZC is smaller than TZCa, the answer at step S4 is YES, and a decision is made at step S5 that the disk being played is not a CD. If, on the other hand, the answer at step S4 is NO, the process proceeds to step S6 at which a decision is made that the disk being played is a CD. In the case of the above-mentioned high density disk such as a DVD, the high frequency signal component of the input signal of the circuit of Fig. 2 is filtered out by the low-pass filter, so that the tracking error component TE passed through the capacitor C1 is within the hysteresis width, and no output signal is generated at the output terminal 203. Conversely, in the case of a CD, the tracking zero-crossing output is generated at the output terminal 203. Hence, by setting the comparison reference of the count value at a value about 5, a discrimination can be performed in such a way that the disk is a CD if the count value is equal to or greater than the comparison reference, and the disk is a high density disk such as a DVD if the count value is smaller than the comparison reference. As described above, a discrimination between the disks CD and DVD is made by counting the number of zero-crossings of the tracking error signal TE. Now, the second embodiment of the present invention will be explained with reference to Fig. 1 and the flowchart of Fig. 6. The flowchart of Fig. 6 shows the counting and comparison process performed by using the circuitry shown in Fig. 3 which uses a comparator without the hysteresis characteristic and without a low-pass filter. As depicted in this flowchart, the operating steps are performed in the similar manner as those steps explained with reference to Fig. 5. Namely, the focus servo is turned on at step S1, and the disk is rotated at step S2. The rotational speed is, for example, 600 r.p.m. Then, the number of tracking zero-crossings TZC is measured at step S3, and detection is made at step S4A as to whether the measured TZC is greater than a comparison reference TZCb which has been set previously. If TZC is greater than TZCa, the answer at step S4A is YES, and a decision is made at step S5 that the disk being played is not a CD. If, on the other hand, the answer at step S4A is NO, the process proceeds to step S6 at which a decision is made that the disk being played is a CD. In the case of the reproduction of a CD, a normal tracking error signal is obtained from the CD. Therefore, the output signal at the output terminal 303 becomes a square-wave signal having 120 cycles per revolution of the disk when the rotational speed of the disk is 600 r.p.m., for example. This is because, if it is assumed that the loaded disk has an eccentricity of 0.1mm, the light beam crosses about 60 tracks when the track pitch is 1.7 µm. The number of zero-crossings of such a square-wave signal is about 240. On the other hand, in the case of the high-density disk such as a DVD, the level of the tracking error signal is very low and near to a degree that the signal is masked by noise signals. Therefore, the square-wave signal at the output terminal 303 becomes a random square-wave signal of multi-cycle. Based on the difference between the tracking error signals from a CD and a high density disk respectively, the discrimination of the disk can be performed by counting the signal at the output terminal 303 by using a microprocessor. For instance, the disk discrimination is performed in such a way that the disk being played is determined to be a CD when count number is equal to or less than 300, and the disk is determined to be a disk other than CD when the count number is higher than 300. The third embodiment of the present invention will be described below. The disk discrimination method in this embodiment uses the radio frequency signal RF from the pickup. With regard to the FSUM signal (the low frequency component FSUM of the focus sum signal) shown in Fig. 4, a normal FSUM signal is retrieved from a CD, whereas the waveform of the FSUM signal is not reproduced from a DVD. Accordingly, by employing a circuit similar to the circuit used in the second embodiment in the FSUMZC generation circuit, the disk discrimination can be performed in the similar manner. As explained in the foregoing, the disk discrimination is performed by using the difference in the output signal waveforms of the tracking error signal or the RF signal from a CD and DVD respectively, in each of the described embodiments. Furthermore, although the disk discrimination process itself has been explained by way of the embodiments of the present invention, it is needless to mention that various processes can be performed after the discrimination of the disk has been made. For instance, a measure is taken to change the operation mode of the disk player from the playing mode to the stop mode or ejection mode after the disk discrimination. Moreover, it is possible to take a measure to display that the disk is not normal or to notify it by sound or voice after the disk discrimination. As will be understood from the above explanation, it is possible according to the present invention to arrange a player capable of reproducing a CD in such a way that the playing of the disk is stopped and the user is notified that the disk is not a CD when it is attempted to reproduce a high density disc such as a DVD by the player of the above-described type. If the apparatus is of the type that a plurality of kinds of disks are respectively played by a plurality of kinds of pickups, the pickup can be changed according to a result of the disk discrimination.

Claims: A disk discrimination apparatus for use in an optical disk reproducing apparatus, comprising: a pickup (101) for reading recorded information on a first optical disk having a predetermined track pitch by using a reading light beam, a tracking error signal generating means (103) for generating a tracking error signal indicating a tracking error produced when reading from said first optical disk; and a disk discrimination means for performing a disk discrimination operation, characterized in that, a counter (105) is provided which counts a number of zero-crossings of a signal carrying information of a relative position of said reading light beam with respect to a recording track, and that, when a second optical disk having a second track pitch smaller than said first track pitch is played by said optical disk reproducing apparatus, said disk discrimination means determines that a disk being played is not said first optical disk, based on a count value of said counter (105). A disk discrimination apparatus as claimed in claim 1, wherein said disk discrimination means performs said disk discrimination by comparing a signal level of a signal (TE) passed through said tracking error signal generating means (103) with a predetermined threshold value. A disk discrimination apparatus as claimed in claim 1, further comprising: a radio frequency (RF) signal generating means for generating an RF signal by reading said first optical disk; and a low-pass filter (107) for extracting a low frequency component of said RF signal to produce a focus sum signal; wherein, the disk discrimination means is performing a disk discrimination operation, when a second optical disk having a second track pitch smaller than said first track pitch is played by said optical disk reproducing apparatus, and is determining that a disk being played is not said first optical disk, based on said focus sum signal. A disk discrimination apparatus as claimed in claim 1, wherein said counter (105) has a hysteresis range in which no count-up occurs, and is operative to count a number of zero-crossings of a tracking error signal produced from output signals of said pickup (101), and said disk discrimination means determines that the disk being played is not said first optical disk when said count value of said counter (105) is lower than a predetermined value. A disk discrimination apparatus as claimed in claim 1, wherein said counter (105) is operative to count a number of zero-crossings of a tracking error signal produced from output signals of said pickup, and said disk discrimination means determines that the disk being played is not said first optical disk when said count value of said counter (105) is higher than a predetermined value.

Inventors: KAMIYAMA HIDEYO, KAMIYAMA, HIDEYO, KAMIYAMA, HIDEYO, C/O PIONEER TOKOROZAWA PLANT
Applicants: PIONEER ELECTRONIC CORP, PIONEER ELECTRONIC CORPORATION
Application year: 1997
Main classification: G11B7
IPC codes: G11B7, G11B19