Reproducing apparatus

Abstract: An optical disc apparatus which records and reproduces desired information by using, for example, a magneto-optical disc and moreover reproduce a compact disc, and adjusts the focus position to the optimum position for each recording medium. For reproducing an optical disc having pits and lands, a magneto-optical disc having grooves and lands carved previously and a composite disc having a pit area and a groove area, the focus bias is switched in accordance with the type of disc or the area of disc to make the optical characteristic of each disc to be optimum, so as to provide an apparatus in which the jitter can be reduced and the error correction rate can be lowered.

Description: The present invention relates to a reproducing apparatus such as, for example, an apparatus for recording and reproducing music data by using such as a magneto-optical disc, and an optical disc apparatus having a reproducible optical disc having pits, such as compact disc, etc. DE-A-3 612 829 which is considered to represent the closest prior art discloses a reproduction and recording apparatus comprising a light receiving means for receiving the reflected light of a light beam irradiated from an optical pick-up to a disc; a generation means for a focus error signal; first and second bias voltage generation means whereby the bias voltage means can be controlled to two different values; switching means for the bias voltage generation means; control means for controlling the switching means during recording, adding means for adding the bias voltage to the focus error signal; and drive means for driving an object lens of the optical pick-up based on the output of said adding means. In an optical disc apparatus such as a compact disc player and so on, an apparatus is disclosed in US-A-4,512,003 in which the reflected light obtained from the compact disc is received and a focus error signal is generated to focus-control on the basis of this focus error signal. Specifically, as shown in Fig. 1, in an optical disc apparatus 1, an optical disc 2 is rotated by a spindle motor 4, and a light beam emitted from the optical apparatus of an optical pick-up 6 radiates to the optical disc 2 in this state. Further, in the optical disc apparatus 1, the reflected light from the optical disc 2 is received by the optical system and its output signal is outputted to a focus error detecting circuit 8. As shown in Fig. 2, in the optical disc apparatus such as a compact disc player, the reflected light from the optical disc is received by a photo detector 10 via a cylindrical lens, wherein the defocusing amount of the light beam is detected by using a so-called astigmatism method. To be specific, in the photo detector 10, a light receiving plane is divided into two toward the radial direction of the optical disc 2, and moreover, is divided into two toward the direction orthogonalizing with the radial direction of the optical disc 2. The focus error detecting circuit 8 Current-Voltage transforms the output current of each light receiving plane by a current-voltage transform circuit 12, and then, outputs it to a differential amplifier circuit 14. Here, the differential amplifier circuit 14 adds the output signals of the light receiving planes positioning toward the direction of a diagonal line, thereafter, a differential signal is generated between the respective added signals. Therefore, as shown in Fig. 3, a focus error signal FE such that the signal level changes in a "S" shape in accordance with the defocusing quantity is generated. In the state that the focus servo loop is not closed, a system control circuit 48 controls a switching circuit 68 by a control signal S1 to switch to B side, and thereafter a SSP (signal servo control processor) 66 generates a focus search voltage signal S2 in order to move an object lens up and down for the disc. Then, the focus search voltage signal S2 moves the object lens up and down via a drive circuit 26 and a focus lens actuator 28. When the object lens comes up to the disc 2, a "S" shape signal is obtained as shown in Fig. 3, and the SSP 66 controls the selecting circuit 68 in order to switch from B side to A side when the coincident point near "0" which is the center of the "S" shape in Fig. 3 is detected. With this control, the focus servo is closed. In the state that the focus servo is closed, the focus error detecting circuit 8 inputs this focus error signal FE to an operational amplifier circuit 22 composed of an inverting amplifier circuit, which has an input resistor 16, a grounding resistor 18 and a feed-back resistor 20, and outputs the output signal of the operational amplifier circuit 22 to a phase compensating circuit 24. The phase compensating circuit 24 compensates the phase of the focus error signal FE and outputs it, and the drive circuit 26 drives a focus lens actuator 28 in accordance with the output signal of the operational amplifier circuit 22. Hence, the focus error detecting circuit 8 moves the object lens up and down in order that the signal level of the focus error signal FE becomes "0" level, so that the defocusing quantity is kept to "0". Because the dispersion or the astigmatism can not prevent in the optical system or the like, in this type of the optical pick-up, a predetermined bias voltage is added on the focus error signal FE and this bias voltage is adjusted so as to focus-adjust. That is, the focus error detecting circuit 8 connects a variable resistor 30 between a positive power source +B and a negative power source -B, and inputs the bias voltage VB formed by this variable resistor 30 to the operational amplifier circuit 22. In this way, in the optical disc apparatus 1, the dispersion, etc. of the optical system can be corrected by adjusting this variable resistor 30. However, in this type of optical disc apparatus, a system which enables not only the playing-back of a compact disc having pits and lands but also the recording and playing-back of information by using an magneto-optical disc having wobbling grooves and lands cut previously, has been provided. In this optical disc apparatus, when the value of the bias voltage VB is changed slowly and the jitter is detected, as shown in Fig. 4, it is recognized that the focus position having the smallest jitter is not coincided between a characteristics of the compact disc (represented by the character "CD") and the magneto-optical disc (represented by the character "MO"). In the conventional optical disc, the bias voltage is fixed and is not changed in accordance with the recording medium. For example, in Fig. 4, the bias voltage VB is adjusted to the range in which the characteristics of the jitter of MO and CD is allowable (the defocusing quantity is near "0"). However, since the bias voltage is differed slightly from the optimum value of the jitter in each disc, in the case where flaws or fingerprints are stuck on the disc, there is a problem that the sound may jump easily. Furthermore, because the bit error rate changes accompanying the change of jitter, in this type of optical disc system, if it can be adjusted to the optimum focus position for each recording medium, the bit error ratio can be improved by this adjustment. In view of the foregoing, an object of this invention is to provide a focus bias switching circuit which adjusts to the optimum focus position for each recording medium. According to the invention, there is provided a reproduction apparatus comprising: a light receiving means for receiving the reflected light of a light beam irradiated from an optical pick-up to a disc; a generation means for generating a focus error signal by using the signal supplied from said light receiving means; a bias voltage generation means for generating first bias voltage; a bias voltage generation means for generating second bias voltage; a switching means for switching said first and second bias voltage generation means selectively; a control means for controlling by switching selectively said switching means in accordance with the type of disc; an adding means for adding the bias voltage from said selected first or second bias means to said focus error signal; and a driving means for driving an object lens of said optical pick-up based on the signal outputted from said adding means. In one embodiment of the invention, there is provided an optical disc apparatus in which an optical disc 2A (Figure 8) and a magneto-optical disc 2B (Figure 9) are kept to be exchangeable, and a light beam emitted from an optical pick-up is focused to the optical disc 2A or the magneto-optical disc 2B to reproduce the recorded data of the optical disc 2A or the magneto-optical disc 2B. The optical disc apparatus 40 of Figure 5 comprises means for generating focus error signal 10, 12 and 14 for receiving the reflected light of the light beam obtained from the optical disc 2A and the magneto-optical disc 2B and for generating a focus error signal FE, a means for correcting focus error signal 16 through 22, 32 and 42 through 52 for adding a bias voltage VB on the focus error signal FE and for correcting the signal level of the focus error signal FE, and focus driving means 24, 26 and 28 for adjusting the focus position of the light beam based on the focus error signal FE corrected by the means for correcting focus error signal 16 through 22, 32 and 42 through 52. The disc judgement means 70 judges whether the set disc is the optical disc 2A or the magneto-optical disc 2B, and then the means for correcting focus error signal 16 through 22, 32 and 42 through 52 switches the bias voltage VB accordingly. Further, in an embodiment of the invention, there is provided an optical disc apparatus 40 in which the light beam emitted from the optical pick-up is focused to the disc to reproduce the recorded data of the optical disc 2A, and moreover the data is recorded in the magneto-optical disc 2B and the recorded data is produced. The optical disc apparatus 40 comprises the means for generating focus error signal 10, 12 and 14 for receiving the reflected light of the light beam obtained from the disc and for generating a focus error signal FE, a means for correcting focus error signal 16 through 22, 32 and 42 through 52 for adding the bias voltage VB on the focus error signal FE and for correcting the signal level of the focus error signal FE, and a focus driving means 24, 26 and 28 for adjusting the focus position of the light beam based on the focus error signal FE corrected by the means for correcting focus error signal 16 through 22, 32 and 42 through 52. In the case that a composite disc 2C, having the inner periphery area in which the predetermined data is previously recorded by forming pits and the outer periphery area in which the magneto recording area is formed and the desired data can be thermomagnetically recorded, is set at the optical disc apparatus 1, the disc judgement means 70 judges the disc, and the means for correcting focus error signal 16 through 22, 32 and 42 through 52 switches the bias voltage VB in accordance with the area of inner periphery side and outer periphery side. The means for correcting focus error signal 16 through 22, 32 and 42 through 52 can add the bias voltage VB on the focus error signal FE via a predetermined time constant circuit 32, 50 and 52. By switching the bias voltage VB correcting the area of signal level of the focus error signal FE between the optical disc 2A and the magneto-optical disc 2B, the optimum focus position can be adjusted for the optical disc 2 and the magneto-optical disc. Further, by switching the bias voltage VB between the area of the inner periphery side and the area of the outer periphery side, it is adjusted to the optimum focus position for the respective areas of the inner and outer periphery sides. At this time, the bias voltage VB is added on the focus error signal FE via the predetermined time constant circuits 32, 50 and 52 so that the defocusing can be prevented previously. In an embodiment of the invention, the bias voltage is switched between the optical disc and the magneto-optical disc, and the signal level of the focus error signal is corrected, so that the optical disc system, which can adjust to the optimum focus position for each recording medium, can be obtained. The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters. Exemplary embodiments of the invention will be described hereinafter, by way of examples only, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing a conventional construction; Fig. 2 is a block diagram showing a conventional optical disc apparatus; Fig. 3 is a signal waveform chart showing the focus error signal thereof; Fig. 4 is a characteristic curve diagram representing the relation ship between the focus error signal and the jitter; Fig. 5 is a block diagram showing an optical disc apparatus according to first and embodiment of the present invention; Fig. 6 is a block diagram showing the optical disc apparatus according to second embodiment of the present invention; Figs. 7A to 7E are signal waveform charts for the explanation of the operation thereof; Fig. 8 is a sectional view of the optical disc having a programming area of pits; Fig. 9 is a sectional view of the magneto-optical disc having a programming area of grooves; and Fig. 10 is a sectional view of the composite disc having a first area with a programming area of pits and a second area with a programming area of grooves. Preferred embodiments of the present invention will be described with reference to the accompanying drawings: (1) First embodiment Referring to Fig. 5 wherein the portions corresponding to those of Fig. 1 are designated with the same reference numerals or characters, 40 denotes an entire optical disc apparatus, wherein the bias voltage VB is switched in accordance with the type of disc 2. In the optical disc apparatus 40, the optical disc 2A or the magneto-optical disc 2B can be set to be exchangeable. The optical disc apparatus 40 can reproduce the optical disc 2A having pits, while the desired information can be recorded and reproduced by using the magneto-optical disc in which the weaving grooves are cut previously. A sectional view of the optical disc 2A is shown in Fig. 8. A laser light is irradiated from the optical pickup to the recording medium surface of the magneto-optical disc 2B (Fig. 9) with the increased laser power. When the temperature exceeds the Curie temperature (approximately, 180 degrees Centigrade), the polarity magnetized in the recording medium is lost, and if the magnetic field is made at the moment when the temperature drops from the Curie temperature, the recording medium is magnetized. The reproducing method of the magneto-optical disc 2B uses the characteristic (which is generally called as "Kerr effect") that when the weak laser light is irradiated to a MO film, the deflection angle of the reflected light changes in response to the polarity of whether N-pole or S-pole. The reflected light is passed through an analyzer so that the polarity of the deflection angle is converted into the intensity of the light to reproduce. The magneto-optical disc 2B have a first area with pits for producing only in the innermost periphery side and a second area with wobbling grooves for recording in the outer area from the innermost periphery side. The sectional view of the magneto-optical disc 2B is shown in Fig. 9. The information of, for instance, the type of disc have been recorded in the first area of the magneto-optical disc 2B, and therefore the data is recorded in the second area based on the information of first area. The optical disc apparatus 40 switches the bias voltage VB in order to correspond to these two types of disc. Specifically, in the optical disc apparatus 40, as shown in Fig. 5, two variable resistors 42 and 44 are connected to the positive and negative power sources +B and -B, and the first and second bias voltages are formed by the respective variable resistors 42 and 44. Further, in the optical disc apparatus 40, the first and second bias voltages is outputted to a selection circuit 46, and the disc judgement means 70 judges the set disc whether the optical disc 2A or the magneto-optical disc 2B. Then, a system control circuit 48 outputs the switching signal FBC on the basis of the judged result, so that the first and second bias voltages are selected and outputted. It is conceived that the refractive index of the surface of disc or the data (in this case, the identification code is recorded previously on the disc) recorded on the disc, and an identification holes spotted on a cartridge can be used as the judgement means 70 in the case where the disc set in a cartridge can be used as the judgement means 70. To be specific, in the optical disc apparatus 40, by switching the contact point between the optical disc and the magneto-optical disc 2B, the bias voltage VB to be outputted to a operational amplifier circuit 22 is switched in accordance with the type of disc. Therefore, in the optical disc system 40, the variable resistors 42 and 44 are adjusted to the optical disc 2A and the magneto-optical disc 2B of which the optical characteristic is supposed to be standard so as to adjust the focus position to the optimum position respectively for the optical disc 2A and magneto-optical disc 2B. Thus, the recorded data is reproduced with a reduced bit error rate. (2) Second embodiment In addition to the optical disc 2A of which programming area is composed of pits and the magneto-optical disc 2B of which the programming area is composed of wobbling grooves, the composite disc, composed of the first programming area with pits on one disc for reproducing operation only, and the second programming area with wobbling grooves for both of record and reproducing operation, is provided. The sectional view of the composite disc 2C is shown in Fig. 10. In the case of the composite disc, the optical disc apparatus 40 switches the contact point of the selection circuit 46 between the first area and the second area. This enables to switch the bias voltage outputted to the operational amplifier circuit 22 for each area. In this manner, in the optical disc system 40, the optimum focus position can be obtained for each area, and the recorded data can be reproduced with a reduced bit error rate. Further, the magneto-optical disc 2B has the pit area and groove area, and the difference between the magneto-optical disc 2B and the composite disc 2C is only one point in which the pit area is used for only a read-in area in the magneto-optical disc 2B and is used for the read-in area and the programming area in the composite disc 2C. In the first embodiment, the bias is not switched between the read-in area with pits and a recordable area with grooves in the magneto-optical disc 2B, but the bias may be switched such like the composite disc 2C. Further, in this embodiment, the optical disc apparatus 40 outputs the output signal of the selection circuit 62 to the operational amplifier circuit 22 via the time constant circuit consisting of the resistors 32 and 50 and a capacitor 52. This enables the voltage inputted to the operational amplifier circuit 22 to change slowly. Specifically, as shown in Fig. 7A to 7E, when the time constant circuit is omitted, the bias voltage VB changes suddenly (Fig. 7A) following the switching of contact point of the selecting circuit 62. In this case, in the optical disc apparatus 60, the signal level of the focus error signal FE changes suddenly (Fig. 7B). That is, in this type of optical disc apparatus 60, if the bias voltage is switched suddenly, it may enter a defocusing state. In this case, it can not be focus-controlled correctly unless it is focus-searched again. Therefore, if the defocusing occurs frequently when the composite disc 2C is recorded and played-back, in the optical disc system 40, it is necessary to focus-search every time when the area is switched between the inner and outer periphery side, and there is a demerit that the access time lengthen. In the optical disc system 60 of this embodiment, however, the output signal of the selection circuit 62 is outputted to the operational amplifier circuit 22 via the time constant circuit so that the sudden change of the bias voltage VB can be prevented previously (Fig. 7C), and the input voltage VT of the operational amplifier circuit 22 can rise slowly (Fig. 7D). In this manner, in the optical disc system 60, the sudden change of the focus error can be prevented previously (Fig. 7E) and the defocusing can be prevented previously. With the above constitution, the bias voltage VT is switched between the magneto-optical disc 2B and the composite disc 2C so that the optimum position can be obtained respectively for the composite disc 2C and magneto-optical disc 2B. This makes it possible to play-back the recording data with a reduced bit error rate. (3) Third embodiment In Fig. 6, 60 shows the optical disc system according to the second invention, wherein the bias voltage VB is switched by the selection circuit 62, and at the same time, the resistor 64 is selected and the output voltage of the selection circuit 62 is kept to "0" level. Specifically, in this type of optical disc apparatus, when the optical disc 2A is exchanged, after the object glass is moved near the optical disc, the object glass goes farther from the optical disc 2 gradually while the focus error signal FE is monitored. This enables it to detect the position of "0" level which is the center of the "S" letter characteristic of the focus error signal FE. Therefore, in the optical disc apparatus 60, the focus control operation is started in this center position so as to focus-control certainly. However, in this focus searching, if the focus error signal FE is biased with a high bias voltage, there is a case that the correct center position can not be detected. For this reason, the optical disc system 60, during focus-searching, switches the contact point to the resistor 64 and drops the bias voltage VB to "0" level. The system control circuit 48 outputs the driving signal of the focus searching, etc., and the servo-control processor (SSP) 66, during focus-searching, drives the drive circuit 26 and moves the position of the object lens sequentially, and at this time, monitors the focus error signal FE and performs the focus searching process. Here, the servo-control processor (SSP) 66 outputs the control signal switching the selection circuit 68 from B side to A side, when the position of "0" level which is the center of "S" letter shape of the focus error signal FE, and at the same time, switches the contact point of the selection circuit 62 to the adjustable resistors 42 or 44 side. Therefore, the focus control operation is started and controlled. With the construction of Fig. 6, during focus-searching, the bias voltage VB is kept to "0" level so as to focus-search certainly. (4) Other embodiments Note that the embodiments discussed above have dealt with the case where the focus signal is generated by using a so-called astigmatism method. However, the present invention is not limited to this, but it may be widely applied to the case where the focus error signal is generated by using various methods for generating focus error signal. Further, the embodiments discussed above have dealt with the case where the desired information is recorded and played-back using a compact disc or a magneto-optical disc. However, the present invention is not limited to this but it can be used widely for the optical disc apparatus which uses a various disc type recording medium. Furthermore, the embodiments discussed above have dealt with the case where the composite disc have the first and second area. However, the present invention is not limited to this but it can used to the disc having a plurality of areas. Furthermore, the arrangement of the pit area and the groove area is not limited in the present invention.

Claims: A reproduction apparatus comprising: a light receiving means (10) for receiving the reflected light of a light beam irradiated from an optical pick-up to a disc; a generation means (14) for generating a focus error signal by using the signal supplied from said light receiving means; a bias voltage generation means (42) for generating first bias voltage; a bias voltage generation means (44) for generating second bias voltage; a switching means (46, 62) for switching said first and second bias voltage generation means selectively; a control means (48, 70) for controlling by switching selectively said switching means in accordance with the type of disc; an adding means (20, 22) for adding the bias voltage from said selected first or second bias means to said focus error signal; and a driving means (26, 28) for driving an object lens of said optical pick-up based on the signal outputted from said adding means. The reproduction apparatus of claim 1, wherein: said control means (48, 70) comprises a judgement means (70) for judging whether the disc is an optical disc with pits and lands or a magneto-optical disc with precut grooves and lands and controls said switching means (46, 62) based on the judgement of said judgement means. The reproduction apparatus of claim 1, operable with a composite disc having a first area with pits and lands and a second area with precut grooves and lands wherein the control means (48, 70) controls the switching means as the reproduction moves from the first area to the second area or from the second area to the first area. The reproduction apparatus of claim 1, 2 or 3, comprising: a time constant circuit (50, 52, 32) between said switching means (46) and said adding means (22). The reproduction apparatus of claim 1, 2, 3 or 4, wherein: said first and second bias voltage generation means each comprises a variable resistor.

Inventors: MIZUKI MASAYUKI, OKA NOBUYUKI, SATO TOSHIO, MIZUKI, MASAYUKI, OKA, NOBUYUKI, SATO, TOSHIO, Mizuki, Masayuki, c/o Intellectual Property Div., Oka, Nobuyuki, c/o Intellectual Property Div., Sato, Toshio, c/o Intellectual Property Div.
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: G11B7
IPC codes: G11B11, G11B19, G11B7, G11B13