Optical disc record reproducing apparatus.

BACKGROUND OF THE INVENTION

0001The present invention relates to an optical disc record reproducing apparatus which forms bits corresponding to recording information on the disc by laser beams to reproduce the record information through variation in the detection signals of the bits.

0002In recent years, an optical disc apparatus using the laser beams has been used. In general, the optical disc may be made as high as two or more in record track density as compared with the magnetic disc to compose large capacity memory, and is characterized in that the laser beams may be focused on the medium surface of disc, the positioning of the beam may be performed through the non-contact by the pregroove track in advance on the disc, so that recording medium may be removable.

0003Also, the various known apparatuses has been provided because of differences in recording, reproducing principle or differences in light source for recording reproducing erasing use or record medium as the optical disc apparatus for information processing use employing the optical disc medium which may be rewritten. For example, in the magneto optic disc apparatus, a semiconductor laser is used as the light source for recording, reproducing and erasing use, a magnetic f-ilm is prepared by the evaporation or sputtering method on the disc as the record medium to record the information through the variation in the magnetizing direction in accordance with the information data.

0004In the conventional magneto optic disc apparatus, the temperature of the magnetic film is locally raised as far as near the curie point by the application of the recording laser beam of the output higher generally as compared within the reproducing, the magnetizing direction is varied by the application of the external magnetic field to effect the recording operation. In the digital information record, the reverse interval of the magnetic polarity to be formed by the use of the above-described method or the interval between the same polarities is varied in accordance with the information data to memory the data.

0005In the optical disc apparatus, the recording conditions vary through the variety of the record sensitivity different in each disc or in the recording position of the disc, the change in the beam power of the laser element, further the change in the recording sensitivity by the ambient temperatures. As a result, the window margin of the reproduction signal is lost by the variety of the record bit length, sc: that the recording density considering it is required to be set, thus resulting in obstacle to the higher density.

0006Also, in the conventional data storing method to be used in the magneto optic disc apparatus, the record bit length along the disc rotating direction of the magnetized reversing portion formed on the disc is required to be strictly controlled. The factors for deciding the record bit length are considered the recording laser power, the recording sensitivity of the magnetic medium. The variation in recording laser power is caused by the variation in the aging change in the output characteristics of the semiconductor laser. Also, the recording sensitivity in the magnetic medium is difficult to be normally controlled constantly in the individual optical magnetic disc and has the variation width. The variation in the recording laser power and the recording sensitivity of the magnetic medium may be easily expected even by the use circumstance, particularly the ambient temperature of the optical magnetic disc apparatus.

0007The changes in the record bit length caused by the above-described variation cause the reduction in the tolerance with respect to the detection window width in the digital recording or the reduction in the signal-to-noise ratio through the movement onto the side of the short length of the record bit length, thus resulting in deterioration in the data error ratio in the worst condition.

SUMMARY OF THE INVENTION

0008Accordingly, an object of the present invention is to provide an optical disc apparatus provided with a record compensating system for controlling the variation in the record bit length.

0009In accomplishing the object, according to one preferred embodiment of the present invention, a laser beam generating means for recording use which generates the optional laser power, a recording means which sequentially generates the laser beams of different power by the laser beam generating means for recording use to form record bits through the application of the laser beams on the disc, a laser power detecting means for detecting the power of the laser beam when the pulse width of-the reproduction signals with respect to the recorded bits becomes given length in length are provided, the recording of the information is recorded in accordance with the detected power of the laser beams.

0010Also, the present invention comprises a laser beam generating means for generating the laser beams of the optional pulse width, a recording means for sequentially generating the laser beams of different pulse width by the laser beam generating means to form the record bits through the application of the laser beams on the disc, a laser beam pulse width detecting means for detecting the pulse width of said laser beam when the pulse width of the reproduction signals with respect to the recorded bit becomes given length, the information is recorded on the disc according to the detected pulse width of the laser beams.

0011Furthermore, the optical disc apparatus of the present invention comprises, in a disc apparatus for information processing use employing the optical disc medium which may be rewritten, a recording means for recording on the optical disc medium the pulse strings having a single period, a difference detecting means for obtaining the . average difference between the high level period and the low level period of the reproduction binary signal of the recorded pulse string, a record compensating means for compensating the duty ratio of the pulse string of the information to be recorded, so that the duty ratio of the reproduction pulse may become constant, in accordance with the above-described difference in the recording means, a controlling means for controlling the record compensation composed of the record by the recording means, the difference detection by the difference detecting means, and the compensation by the record compensating means. In order to make constant the duty ratio of the record pulse to be reproduced in this manner, the pulse string having the single period of the integer multiplication of the record bit period is recorded in trial to obtain the shift of the duty ratio from the duty ratio in the reproduced signal. Also, the duty ratio is kept slided in advance in the recording of the information in accordance with the shift to keep the duty ratio of the reproduction pulse at the given value.

BRIEF DESCRIPTION OF THE DRAWINGS

0012These objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which; <ul id="ul0001" list-style="none"><li>Fig. 1 is a block circuit diagram showing the basic construction in a first embodiment of the present invention;</li><li>Fig. 2 is a block diagram showing the construction of a pulse width discriminator in the first embodiment of Fig. 1:</li><li>Fig. 3 is a graph showing the signal wave-forms generated in the first embodiment of Fig. 1;</li><li>_Fig. 4 is a block circuit diagram showing the basic construction in a second embodiment of the present invention;</li><li>Fig. 5 is a block diagram showing the construction of a pulse width variable circuit in the second embodiment of Fig. 4;</li><li>Fig. 6 is a block diagram showing the construction of a pulse width discriminator in the second embodiment of Fig. 4;</li><li>Fig. 7 is a graph showing of the signal wave-forms generated in the second embodiment of Fig. 4;</li><li>Fig. 8 is a block circuit diagram of a magneto optic disc apparatus provided with a record-compensating system in a third embodiment of the present invention;</li><li>Fig. 9 is a concrete circuit diagram of the record pulse generating circuit in the third embodiment of Fig. 8;</li><li>Fig. 10 is a concrete circuit diagram of the reproduction duty ratio detecting circuit in the third embodiment of Fig. 8;</li><li>Fig. 11 is a time chart of the various signals in the reproduction duty ratio detecting circuit in the third embodiment of Fig. 8; and</li><li>Fig. 12 is a graph of the digital values of the up, down counter in the third embodiment of Fig. 8.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0013Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

(First Embodiment)

0014Referring now to Fig. 1, there is shown, the basic construction of an optical disc apparatus according to a first preferred embodiment of the present invention, which includes an optical disc 1, and an optical pickup 2 which is adapted to record and reproduce the information of the optical disc 1. The optical pickup 2 is composed of a laser 2a for generating the laser beams of optional laser power, and a reproduction signal detector 2b. Reference character 3 is a laser driver for driving the laser 2a. Reference character 4 is a D/A converter which supplies the driving signal to the laser driver 3. Reference character 5 is a centrolling circuit which feeds the data to the D/A converter 4 so as to generate the laser beams, by the optical pickup 2, different in laser power sequentially with the constant frequency prior to the actual information recording. Reference character 6 is an. amplifier for amplifying the output of the reproduction signal detector 2b. Reference character 7 is a comparator which is adapted to slice in level the output of the amplifier 6 to output the pulse signal. Reference character 8 is a pulse width discriminator which is adapted to discriminate of the size relation between the pulse width of the pulse from the comparator 7 and a given value.

0015Fig. 2 shows the construction of the pulse width discriminator 8. Reference numeral 8a is a positive edge detector for detecting the rising edge of the pulse from the comparator 7. Reference character 8b is a monostable multivibrator which outputs the reference pulses of a constant pulse width for each of the rising edges detected by the positive edge detector 8a. Reference character 8c is a flip-flop which is adapted to sample the pulse from the comparator 7 by the rising edge of the reference pulse from the monostable multivibrator 8b. The flip-flop 8c reverses the output through the size of the pulse length on the side of the low level of the reference pulse as compared with the pulse size on the side of the high level of the pulse from the comparator 7.

0016Fig. 3 shows the signal wave-forms generated at the various, portions of this optical disc apparatus, reference character a is the record bit of the optical disc, reference character b is the output of the amplifier 6, reference character c is the output of the comparator 7, reference character d is the output of the monostable multivibrator 8b, reference character e is the output of the flip-flop 8c.

0017The operation of the optical disc apparatus, wherein such laser beam power as the duty ratio of the reproduction signal becomes 50% is provided will be described hereinafter.

0018The controlling circuit 5 feeds the data to the D/A converter 4 to sequentially vary the laser driving current in accordance with the signals of a constant frequency, so that the data is converted into the analog signal by the D/A converter 4 and is fed to the laser driver 3. The laser driver 3 drives the laser 2a of the optical pickup 2 in accordance with the analog signal to record a constant frequency, which is different in laser beam power sequentially with respect to the rotating optical recording disc 1. When the recordings are performed sequentially with the laser beam power being P1, P2, --- P5 respectively in the- periods tl, t2, ---, t5, the recorded bits shown in Fig. 3a -are formed on the optical disc 1. The laser beam power P1 in the period tl is smaller than the laser beam power P2 in the period t2. Likewise, the laser beam power P2 is smaller than the laser beam strength P3. The P3 is smaller than the _P4. The P4 is smaller than the P5. Accordingly, the recorded bit a has the period tl shortest, the period t5 longest.

0019Then, the recorded bit a formed on the optical disc 1 is detected by the reproduction signal detector 2b, is amplified by the amplifier 6, is converted into the signal shown in Fig. 3b, thereafter is sliced in level by the comparator 7 to provide the pulse signal of Fig. 3c. The pulse signal c has the period tl shortest in the pulse length on the side of the high level, the periods t2, t3, --- sequentially longer. In the pulse signal c, the rise edge is detected by the positive edge detector 8a in the pulse width discriminator 8, the monostable multivibrator 8b is started by the rising edge. As a result, every time the rise edge of the pulse signal c is generated from the monostable multivibrator 8b, the reference pulse signal d of 50% in duty ratio is outputted.

0020In the periods tl and t2, the duty of the pulse signal c is deviated, and the high-level pulse length of the pulse signal c is shorter than the low-level pulse length of the reference pulse signal d. Thus, the output e of the flip-flep 8c remains kept in the low level.

0021Then, in the period t3, when the high-level pulse length of the pulse signal c becomes equal to the low-level pulse length of the reference pulse signal d, the output e of the flip-flop 8c is reversed to the high level. Thereafter, in the period t4, t5, the high-level pulse length of the pulse signal c becomes longer than the low-level pulse length of the reference pulse signal d, so that the output e of the flip-flop 8c is kept high in level.

0022The duty ratio of the pulse signal c in the period t3 during which the output e of the flip-flop 8c is reversed, i.e., of the reproduction signal is 50%, and the laser beam power in the period 3t is P3. Accordingly, it is judged that the laser beam power is required to become P3 in order to perform the optimum recording that the duty ratio of the reproduction signal is 50%. Thereafter, the actual information is recorded by this laser beam power P3.

0023In this embodiment, the decision is performed by the use of the pulse length on the side of the high level of the pulse signal c and the rising edge, but it may be performed by the use of the pulse length on the side of the low level of the pulse signal c and the falling edge. Furthermore, the higher precise setting of the laser beam power may be performed if the decision is performed by the use of both the pulse lengths on the side of the high level of the pulse signal c and on the side of the low level. As described hereinabove, in this embodiment, the recording operation is performed while the laser beam power being sequentially changed to provide the laser beam power when the pulse width of the reproduction signal becomes a given length. Thus, even if the recording sensitivity is different for each disc or the power of the laser beam is varied in accordance with temperatures, the optimum recording conditions may be set under the condition of the disc and circumference conditions to be used to improve the reliability of the reproduction signal and to realize the higher density of the information record.

(Second Embodiment)

0024Fig. 4 shows the basic construction of the optical disc apparatus according to a second preferred embodiment of the present embodiment. Reference character 11 is an optical disc corresponding to the one of the first embodiments. Reference character 12 is an optical pickup which is adapted to record and reproduce the information of the optical recording disc 11. The optical pickup 12 is composed of a laser 12a for generating the laser beam of the optional pulse width and a reproduction signal detector 12b. Reference character 13 is a laser driver for driving the laser 12a. Reference character 14 is a width varying circuit which feeds the driving signal to the laser driver 13 so as to generate the laser beams, by the optical pickup 12, different-in pulse length sequentially with the constant frequency prior to the actual information recording. Reference character 15 is a controlling circuit which feeds a constant frequency of pulse signal to the pulse width varying circuit 14 and feeds the selection signal of the multiplexer to be described later. Reference character 16 is an amplifier for amplifying the output of the reproduction signal detector 12b. Reference character 17 is a comparator which slices in level the output of the amplifier 16 to output the pulse signal. Reference character 18 is a pulse width discriminator which discriminates the size relation between the pulse width of the pulse signal from the comparator 17 and a given value.

0025Fig. 5 shows the construction of the pulse width varying circuit 14. Reference characters 14a, 14b, 14c, 14d are delay lines which delay the input signals respectively by time t to output them. The delay line 14a delays by time t a constant frequency of pulse signal from the controlling circuit 15 to output it, the delay line 14b delays by time 2t, the delay line 14c delays by time 3t, the delay line 14d delays by time 4t. Reference character 14e is a multiplexer which selectively outputs, in accordance with the selection signal from the control circuit 15 the constant frequency of pulse signals from the controlling circuit 5 and one of the pulse signals to be outputted from the delay lines 14a, 14b, 14c, 14d. Reference character 14f is a _positive edge detecting circuit for detecting the rising edge of the output signal of the multiplexer 14e. Reference character 14g is a negative detecting circuit for detecting the falling edge of the output signal of the delay lire 14b. Reference character 14h is a R-S flip-flop which is reset by the output of the positive edge detecting circuit 14f and is set by the output of the negative edge detecting circuit 14g.

0026Fig. 6 shows the construction of the pulse width discriminator 18. Reference character 18a is a positive edge detecting circuit for detecting the rising edge of the pulse signal from the comparator 17. Reference character 18b is a monostable multivibrator which outputs the reference pulse of a constant pulse width for each of the rising edges detected by the positive edge detecting circuit 18a. Reference character 18c is a flip-flop which samples the pulse from the comparator 17 by the rising edge of the reference pulse signal from the monostable multivibrator 18b. The flip-flop 18c is reversed in output by the size of the pulse width on the low-level side of the reference pulse as compared with the pulse width on the high-level side of the pulse from the comparator 17.

0027Fig. 7 shows the signal wave-forms generated at the various portions of the optical dise apparatus. Reference character a is a constant frequency of pulse signal which is fed to the pulse width varying circuit 14 from the controlling circuit 15. Reference characters b, c, d, e are cutputs of the delay lines 14a, 14b, 14c, 14d respectively. Reference character f is the output of the multiplexer 45. Reserence character q is an output of the positive edge detecting circuit 14f. Reference character h is an output of the negative edge detecting circuit 14g. Reference character j is an output of the R-S flip-flop 14h. Reference character K is a recorded bits of the optical record disc 11. Reference character ℓ is an output of the amplifier 16. Reference character m is an output of the comparator 17. Reference character n is an output of the positive edge detecting circuit 18. Reference character o is an output of the monostable multivibrator 18b. Reference character p is an output of the flip-flop 18c.

0028The operation of the optical disc apparatus in the embodiment will be described hereinafter.

0029The pulse signal a of a constant frequency from the controlling circuit 15 is fed to the pulse width varying circuit 14. In the pulse width varying circuit 14, the multiplexer 14e outputs a plurality of signals such as the pulse signal a to the period tl in accordance with the selection signal from the controlling circuit 15, the pulse signal b which is delayed by time t from the pulse signal a to the period t2, the pulse signal c which is delayed by time 2t from the pulse signal a to the period t3, the pulse signal d which is delayed by time 3t from the pulse signal tc the period t4, and the pulse signal e which is delayed by time 4t from the pulse signal a to the period t5 respectively. And the positive edge detecting circuit 14 outputs the short pulseg by the rise edge of the output signal f of the multiplexer 14e and the negative edge detecting circuit 14g outputs the short pulse h by the fall edge of the output signal of the delay line 14b.

0030Now, when the output signal a of the controlling circuit 15 is outputted as the output signal f from the multiplexer 14e by the selection signal i from the controlling circuit 15 in the period tl, the R-S flip-flop 14h is reset by the rise of the signal a and is set by the fall of the signal c delayed by time 2t from the pulse signal a, so that the output j of the R-S flip-flop 14h becomes a signal short by 2t in the pulse width on the high-level side with respect to the signal a. As described hereinafter, the output j of the R-S flip-flop 14h becomes a signal, which is short by t in the pulse width on the high-level side with respect to the signal a by the signal b and the signal c which are delayed by at from the signal a in the period t2. In the period t3, the R-S flip-flop 14h is reset by the rise of the signal c and is set by the fall of the signal c, so that the output j becomes a signal-of the high-level-pulse width which has no increase, decrease in the signal a. In the period t4, the output j becomes a signal which is long by t in the high-level pulse width with respect to the signal a by the signal d and the signal c delayed by 3t from the signal a. In the period t5, the output j becomes a signal which is long by 2t in the high-level pulse width with respect to the signal a by the signal e and the signal c delayed by 4t from the signal a. And the signal j of the high-level pulse width different respectively in the period tl, t2, t3, t4, t5 is sequentially fed to the laser driver 13. The laser driver 13 drives the laser 21a of the optical pickup 12 in accordance with this signal j so that the laser beam of the pulse width corresponding to the signal j is applied upon the rotating optical record disc 11. As a result, the recorded bit K which is different respectively in length in the periods tl, t2, --- t5 is formed on the optical record disc 11.

0031Then, the record bit K formed on the optical record disc 11 is detected by the reproduction signal detector 12b of the optical pickup 12, is amplified by the amplifier 16 and is converted into the signal ℓ. Thereafter, it is sliced in level by the comparator 17 so that the pulse signal m is provided. This pulse signal m is shortest in the period tl in the pulse width on the high-level side, becomes sequentially longer as the period moves to the period t2,-the period t3, ---, and becomes longest in the period t5. The pulse signal m has the rise edge detected by the positive edge detecting circuit 18a in the pulse width discriminator 18, the monostable multivibrator 18b is started by the defection signal n of the rising edge. As a result, a reference pulse signal o of a constant pulse width is outputted each time the rise edge of the pulse signal m is caused from the monostable multivibrator 18b.

0032In the periods tl and t2, the duty of the pulse signal m is deviated, the high-level pulse width is shorter than the low level pulse width of the reference pulse signal o, so that the output p of the flip-flop 18c remains low in level.

0033Then, in the period t3, when the high-level pulse width of the pulse signal m becomes equal to the low level pulse width of the reference pulse signal o, the output p of the flip-flop 18c is reversed to the high level. Thereafter, in the period t4, t5, the high-level pulse width of the pulse signal m becomes longer than the low-level pulse width of the reference pulse signal o, so that the output p of the flip-flop 18c retains the high level.

0034The duty ratio of the pulse signal m, i.e., the reproduction signal in the period t3 during which the output p of the flip-flop 18c is reversed is 50%. This is because the pulse width of the laser beam is determined through the selection of the delay signal c in the pulse width varying circuit 14. Accordingly, it is judged that the pulse width of the laser beam is required to be set through the selection of the delay signal c in order to perform the optimum recording that the duty ratio of the reproduction signal is 50%. Thereafter, the actual information is recorded by the laser beam of the selected pulse width.

0035In this enbediment, the decision is performed by the use of the pulse width on the sick cf the high level of the pulse signal m and the rising edge, but it may be performed by the use of the pulse width on the side of the low level of the pulse signal m and the falling edge. Furthermore, the higher precise setting of the pulse width of the laser beam may be performed if the decision is performed by the use of both the pulse widths on the side of the high level of the pulse signal m and on the side of the low level. As described hereinabove, in the second embodiment of the present invention, the recording operation is performed while the pulse width of the laser beam being sequentially changed to select the pulse width of the laser beam when the pulse width of the reproduction signal becomes a -given length. Thus, even if the recording sensitivity is different for each disc or the light power of the laser beam is varied in accordance with temperatures, the optimum recording conditions may be set under the condition of the disc and circumference conditions to be used to improve the reliability of the reproduction signal and to realize the higher density of the information record.

(Third Embodiment)

0036A magneto optic disc apparatus in a third embodiment of the present invention will be described with reference to Figs. 8 to 12.

0037In the magneto optic disc apparatus of Fig. 8, the duty ratio of the reproduction signal during the trial recording is detected to suppress the variation in the record bit length so as to compensate the duty ratio of the recording pulse during the actual recording. In the magneto optic disc apparatus, a controlling portion 21 of the optical disc apparatus feeds to a modulator 22 the information data to be recorded during the recording operation. The modulator 22 modulates the information data in digital to feed the data to a record pulse generating circuit 23 as the pulse string. The record pulse generating circuit 23 generates the record pulses from the pulse strings after the modulation to feed them to a laser driving circuit 24. The laser driving circuit 24 applies the record pulse current upon the semiconductor laser of an optical head 25 by the record pulse and the control signal from the controlling portion 21 of the optical disc apparatus. The optical head 25 is provided with the semiconductor laser to effect the recording operation on the magneto optic disc.

0038During the reproduction, the reproduction signal which has been reproduced from the magnetic optic disc by the optical head 25 is shaped in wave-form through the amplification and the band-pass in a wave-form shaping circuit 26, then is digitalized in a wave-form processing circuit 27, further is demodulated by a demodulator 28 and is fed to the control portion 21 of the optical disc apparatus.

0039Through the reception of the record corrocting command from the control portion 21 of the cptical disc apparatus during the trial recording operation, a record correction control portion 31 converts the record pulse string into the pulse string having the single period of the integer multiplication of the record bit period in the record pulse generating circuit 23, the control portion 21 of the optical disc apparatus controls the laser driving circuit 24 so as to record the record pulse string in the zone-not-recorded on the disc. On the other hand, the reproduction signal of the single-period pulse string recorded has the wave-form shaped in the wave-form shaping circuit 26 and, thereafter, is digitalized through the level slice to feed to a reproduction-duty-ratio detecting circuit 30. The reproduction-duty-ratio detecting circuit 30 detects the difference between the time length of the "1" of the binary-coded output signal of a comparator 29 and the time length of the "0" to feed it to the record pulse generating circuit 23. The record-correction control portion 31 controls the record pulse generating circuit 23 and the reproduction duty-ratio detecting circuit 30 in the record correcting operation.

0040The record correction in-this embodiment will be described hereinafter in more detail.

0041- The record pulse generating circuit 23 shown fully in Fig. 9 generates the pulse string having the single period of the integer multiplication of the record bit period as the record pulse when the record-correction control portion 31 transmits the signal by the command of the control portion 21 of the optical disc apparatus, and corrects the duty ratio of the record pulse of the actual information in accordance with the correction amount of the duty ratio detected by the reproduction duty-ratio correcting circuit 30 through the single period pulse string. Namely, when a first multiplexer 101 is switched by the signal from a control line 302 from the record-correction control portion 31 in the record pulse generating circuit 23, the pulse string having a single period generated by a single period generating circuit 107 passes through the first stage of a record duty ratio correcting circuit 102 to apply the correction of the duty ratio of a certain constant value, continuously passes through the second record duty-ratio correcting circuit, which is described hereinafter, to apply the correction of the duty ratio, the last record pulse string passes through a signal line 307 to go to the laser driving circuit 24. In the second stage of record duty-ratio correcting circuit; the output signal of the first stage of record duty ratio correcting circuit 102 is fed, on one hand, into one input terminal of a flip-flop circuit 111 through an edge detecting circuit 109 for detecting the rise edge by the logical differentiation, and passes, on the other hand, through the delay circuit com- pesed of a delay element 103 having a plurality of output taps and a second multiplexer 104 for selecting the output tap of the delay element 103, and is fed to the other input terminal of the flip-flop circuit 111 through an edge detecting circuit 110 for detecting the rise edge by the logical differentiation. The output signal of the flip-flop circuit 111 becomes the record pulse and is fed to the laser driving circuit 24. In the above-described delay circuit, the second multiplexer 104 is used for the selection of the step from the taps of the (2^N-M-1 of the delay element 103, but a latch circuit 106 is used for the selection input of the second multiplexer 104. The preset terminal 312 of the latch circuit 106 is set at the early stage in advance to give the selection input value 309 to the second multiplexer 104 when the power supply is put to work. Furthermore, an addition and subtraction device 105 is provided which effects the adding or subtracting operation between the output value of the latch circuit 106 and the value of an input line 311 from the reproduction duty ratio detecting circuit 30 for inputting operation to the latch circuit 106. When the correction amount which is provided from the reproduction of the trial record is fed to the adding/subtracting device 105 from the reproduction duty-ratio detection circuit 30, the output value of the latch circuit 106 is changed. Also, the first stage of record duty ratio correcting circuit 102 has a certain given amount of bias correction so that the optimum record duty ratio expected in advance may be provided with respect to the initial set value. A signal 401 of the reproduction pulse string in a case where the trial record is performed immediately after the power supply is put to work in accordance with the record conditions is shown in Fig. 11, wherein the record conditions are optimum, a reproduction pulse string where the duty ratio shown in a solid line in the drawing is 1 is provided.

0042On the reproduction side, the reproduction signal from the optical head 25 in a case where the single period pulse string is recorded in trial is processed properly in the wave-form by the wave-form shaping circuit 26, and thereafter is digitalized by the comparator 29. Here, for the faithful reproduction of the duty ratio of the reproduction signal in the comparator 29, the level slice is performed with the intermediate value of the envelope of the reproduction signal to use the digitalizing system. The reprcduction duty-ratio detecting circuit 30 detects the duty ratio of the digital pulse string provided in this manner to recognize the correction amount of the recording cenditions to feed it to the record pulse generating circuit 3.

0043The detailed block diagram of the reproduction duty ratio circuit 30 is shown in Fig. 10. Also, the timing charts of the various signals are shown in Fig. 11. The up, dcwn counter 201 switches the digital direction by the values of "1" and "0" of a reproduction pulse string signal 401 or the record pulse string which has a sufficiently high frequency with respect to the reproduction pulse string is supposed to be a clock input signal 403. A latch circuit 202 latches the output signal 407 of an up, down counter 201. A bit shifter 203 sends the upper bit, which is equivalent to the average value of the duty-ratio-shift, of the output signal of the latch circuit 202 to the record pulse generating circuit 23 through the control line 311. A flip-flop 205 shows the repetition of the reproduction pulse string. A counter 2C4 counts the repeating time to decide the operation period of the up, down counter 201.

0044The operations of the record correction and the correction-amount detection in the magneto optic disc apparatus will be described in accordance with Figs. 11 and 12. A,càse will be ccnsidered where the reproduction signal 401 of the single-period pulse string recorded in trial is the pulse string which is out of the reproduction duty-ratio shown in the dotted line in Fig. 11. The N bit high-speed up, down counter 201 is initialized by the preset terminal 402 into the (2^N-1) ) value prior to the counting. The N bit high-speed up, down counter 201 of the reproduction duty-ratio detecting circuit 30 performs the counting operation of the clock signal 403 when the digital command signal 404 to be given from the record-correction control portion 31 becomes low in level and the control signal 40₅ showing the detection period decided by the counter 204 where the digital of the reproduction pulse strings m are counted is low in level. When the difference between the period of "1" of the reproduction pulse string and the period of "0" thereof is obtained by the counting across the plurality (m) of reproduction pulse strings, the difference is detected across the reproduction pulse strings m to perform the average process. It is to be noted that the signal 406 is used to restore the flip-flop 205 to the initial condition.

0045When each of the m th number of reproduction pulse strings is out of the duty ratio by time Δi (i = 1, 2, --m) , the digital value in each time of the up, down counter 201 is shown by Fig. 12. After the lapse of the digital period shown by the signal 405, the last value<maths id="math0001" num=""><img file="EP0213623A2_D0001.tif" /></maths>is provided. Here reference character Tc is the repeating period of the clock input 403. Also, assume that the digit of the reproduction pulse string is m = 2^M, the average which is out of the reproduction duty ratie is<maths id="math0002" num=""><img file="EP0213623A2_D0002.tif" /></maths>wherein the Δ shows the average value of the Δi (i= 1, 2, ---_-m), 2^N-1_> 2^M+1 Δ/Tc. Furthermore, the bit shifter 203 is used with respect to the last value, the upper (N-M-1) bit corresponding to the average value is fed to the record pulse generating circuit 23 through the output line 311. Here the most significant bit shows the direction which is out of the reproduction duty ratio. Also, the other (N-M-2) bit shows a value proportional to the average shift amount (2A/Tc). However, when the period of the "0" is longer on the average than the period of the "1" as the signal 401 shows in the dotted line in Fig. 11, the output is provided in complement expression of the binary number, the subtraction is performed through the complement addition by the adding/subtracting device 105 of the record pulse generating circuit 3.

0046In the present embodiment, the output data 409 provided by the above-described method as the input data to the record pulse generating circuit 23 in Fig. 9 is directly given to add the correction equivalent to the duty ratio shift amount (2A/Tc) during the reproduction time in the subsequent actual information recording. Namely, the value of the latch circuit output 309 showing the correction amount during the trial recording is increased or decreased by the most significant bit of the input line 311 through the use of the adding/subtracting circuit 105 in Fig. 9 or the delay amount 2 per one step of the delay element 103 is required to be τ = Tc. In the first stage of record duty ratio correcting circuit 102, a given bias correction is performed so that the optimum record duty ratio to be expected may be provided. When the bias correction is kept properly set, the duty ratio correction amount to be detected by the reproduction duty ratio detecting circuit 30 becomes a small value through the aging changes or the variations in the using circumference. As the second stage of record duty-ratio circuits 103 through 106, 108 through 111 provides the correction accuracy of ± Tc with the least delay amount as Tc.

0047After the above correction is over, the recording of the single period pulse string is removed.

0048The second correcting system shown in the present embodiment may be generally applied to the optical disc apparatus for information processing use employing the optical disc medium which can be rewritten.

0049The record correcting system shown in the present embodiment may be controlled not only while the power supply is put to work, but also during the unoccupied time when the recording, reproducing, erasing operations to the information record region are not required from the upper apparatus. Also, the controlling operation may be performed so that the value of the record correction may be renewed at each of the proper time intervals.

0050The record correcting system in the present embodiment of the present invention provides the following offects.

0051<ul id="ul0002" list-style="none"><li>(1) As the deviation from the optimum conditions may be detected directly from the reproduction wave-form, the correction amount may be determined by one trial only.</li><li>(2) As all the processings are performed by the digital circuit, the operation is stable.</li><li>(3) As the correction accuracy of the ± Tc is provided with respect to the period Tc of the input clock of the up, down counter, the Tc may be made sufficiently small with respect to the record bit length, which may make it possible to provide the correction of higher accuracy.</li><li>(4) As the processing operation for average may be easily realized as shown even in the embodiment, the factors except for the record conditions to be caused by flaws on the disc may be removed.</li><li>(5) Also, the repetition of the trial at the proper time interval allows the time lapse after the apparatus power-supply is put to work and the characteristic variation between the respective discs during the disc exchange to be coped with.</li></ul>

0052Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as included therein.