JP2005158241A - Information reproducing apparatus and its in-line circuit, and method for implementing in-line circuit on information reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rationalize a circuit and to attain low-cost in a DVD-RAM reproducing signal in-line circuit used for an optical disk reproducing apparatus. <P>SOLUTION: The information reproducing apparatus comprises an input amplifier 1 to which an RF signal reproduced from an optical disk is inputted; a high-pass filter 10 to which the output of the input amplifier 1 is inputted; an AD converter 5 to which the output of the high-pass filter 10 is inputted; a lag lead filter 6 to which the output of the AD converter 5 is inputted; and a demodulator 7 for digitally processing the output of the lag lead filter 6 to demodulate it as a binary signal. Therefore, an optical disk reproducing apparatus that realizes a DVD-RAM reproducing function at low cost can be realized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disk reproducing apparatus as an information reproducing apparatus, and particularly to an address area (hereinafter referred to as an ID area) and a data area for an optical reproduction signal reproduced by an optical pickup from a track formed on the optical disk. And an in-line circuit that eliminates the difference in the DC level of the optical reproduction signal and an improved mounting method thereof.

  Conventionally, for example, an inline circuit of an optical disk reproducing apparatus that reproduces a DVD-RAM disk as an information recording medium is described in Patent Document 1.

  FIG. 8 shows the overall configuration of an optical disk reproducing apparatus using this type of inline circuit. As shown in FIG. 8, the inline circuit 400 is a track formed on a DVD-RAM disk 200 as an information recording medium. Are provided between the optical pickup 300 for reproducing the information and the signal processing circuit 500 for processing the reproduction signal. In addition to controlling the signal processing circuit 500, the system controller 600 controls the entire optical disk reproducing apparatus, such as the rotational speed control of a spindle motor (not shown) that rotates the DVD-RAM disk 200 and the tracking control of the optical pickup 300. I do.

  FIG. 9 shows a more detailed configuration of the inline circuit 400 in the conventional optical disk reproducing apparatus. In FIG. 9, reference numeral 51 denotes an input amplifier for amplifying an RF signal which is an optical reproduction signal from the optical pickup 300 in FIG. 53 is an external capacitor for correcting the DC level of the optical reproduction signal amplified by the input amplifier 51, and 54 and 55 are for selecting one of the capacitors 52 and 53 according to the ID region discrimination signal 62. The switches 56 and 57 are resistors, and the time constant for DC level correction is determined in combination with the capacitors 52 and 53. 58 is a switch for rapidly correcting the fluctuation of the DC level of the optical reproduction signal in accordance with the lead-in signal 63, 59 is a buffer amplifier for amplifying the optical reproduction signal after DC correction, and 60 is an output signal of the buffer amplifier 59. An AD converter 61 that performs AD conversion is a slicer as a comparator that binarizes the output signal of the AD converter 60 and outputs the result to the signal processing circuit 500 of FIG. Reference numeral 62 denotes an ID area determination signal for turning on one of the switches 54 and 55, and 63 is a pull-in signal for turning on / off the switch 58. The circuits up to the previous stage of the AD converter 60, that is, the input amplifier 51, the external capacitors 52 and 53, the switches 54 and 55, the resistors 56 and 57, the switch 58, and the buffer amplifier 59 constitute an inline circuit 400. Yes.

  In this in-line circuit 400, the resistor 57 constitutes a high-pass filter in combination with either one of the capacitors 52 and 53. This high-pass filter converts the DC component in the optical reproduction signal into the group delay characteristic of the RF signal. Remove without affecting. Usually, the cut-off frequency is set to about 100 Hz. The resistor 56 is inserted in parallel with the resistor 57 by the switch 58 for the purpose of shortening the time constant of the high-pass filter, that is, for the purpose of speeding up the waveform convergence when removing the DC component.

  FIG. 10 shows operation waveforms of the inline circuit of FIG. FIG. 10A shows an optical reproduction signal which is an input signal of the input amplifier 51 and which reproduces a track of the optical pickup 300. In the figure, an area where the DC level is high is an ID area, and other areas. Shows signals when data areas are being reproduced. FIG. 10B shows an ID area discrimination signal 62, which becomes “H” when the portion corresponding to the ID area in the track is reproduced, turns on the switch 54, turns off the switch 55, and vice versa at other times. That is, the switch 55 is turned on and the switch 54 is turned off. FIG. 10C shows a pull-in signal. The switch 58 is turned on for a certain period from the time when the reproduction area is switched, that is, when the data area and the ID area are switched. FIG. 10D shows an input signal of the AD converter 60.

  FIG. 11 is a diagram showing the structure of the ID portion of the DVD-RAM disk, where 100 is a groove that is a guide groove and a mark recorded on a land that is an area between the grooves, and 101 is an ID area. It is an emboss mark.

  As shown in FIG. 11, since the data region in the track has a land / groove structure, the portion without the mark 100 does not have the maximum reflectance, whereas the ID region has an embossed structure. In the portion without 101, the mirror reflectance is obtained. For this reason, as shown in FIG. 10A, the DC levels of the reproduction signals in the data area and the ID area are greatly different.

  By the way, the input range of the AD converter 60 is set in accordance with the amplitude of the RF component of the reproduction signal as shown in FIG. 10A, and is smaller than the amplitude including the DC level fluctuation. It is necessary to suppress and perform AD conversion.

  For this reason, as shown in FIG. 9, the data area capacitor 52 and the ID area capacitor 53 are used in combination as the coupling capacitors, and the switches 54 and 55 are controlled by the ID area discrimination signal 62 to perform switching. Thus, as shown in FIG. 10 (d), a signal having a uniform DC level is generated.

  In order to quickly charge the DC voltage in the data area and the ID area, a resistor 56 for the capacitors 52 and 53 is inserted in parallel with the resistor 57 by the switch 58 to shorten the time constant, and to start the ID area. And the convergence of the reproduction signal at the end time is accelerated.

  As described above, in the in-line circuit of the conventional optical disk reproducing apparatus, when the track formed on the optical disk is reproduced, it is determined whether the area being reproduced corresponds to the ID area or the data area. Capacitors 52 and 53 need to be switched, and in order to perform this switching, a circuit for generating an ID area determination signal is required in addition to the inline circuit.

  FIG. 12 is a block diagram of a circuit for generating the ID region discrimination signal, and FIG. 13 shows the operation waveform.

  In the figure, reference numeral 80 denotes a light receiving element of the optical pickup 300 of FIG. 8, which is divided into four as shown in the figure with respect to the track direction of the optical disk. 81 and 82 are adders and 83 is a subtractor. The adders 81 and 82 calculate the sum output of the light receiving elements A and D and the sum output of B and C in the track left and right direction, respectively. The differential RF signal is generated by subtracting the output signal of the adder 82 from the output signal 81. A buffer amplifier 84 amplifies the differential RF signal. Reference numerals 85 and 86 denote resistors and capacitors that constitute a high-pass filter, which removes a direct-current component from the differential RF signal output from the buffer amplifier 84 and assists processing based on a subsequent threshold value. A buffer amplifier 87 amplifies the output of the high pass filter. Reference numerals 90 and 91 denote comparators that compare the differential RF signal output from the buffer amplifier 87 with the upper (UPPER) threshold value 88 and the lower (LOWER) threshold value 89, respectively. 92 is an OR circuit that generates a logical sum of the output signals of the comparators 90 and 91, and 93 is a monostable multivibrator (hereinafter referred to as a mono-stable multivibrator) that shapes the waveform into a continuous binary signal by removing the RF frequency from the output signal of the OR circuit 92 Called multi-circuit).

  FIG. 13A shows the differential RF signal in the data area and the ID area, and the levels of the upper threshold value 88 and the lower threshold value 89. 13 (b) shows the output of the upper comparator 90, FIG. 13 (c) shows the output of the lower comparator 91, and FIG. 13 (d) shows the output of the mono-multi circuit 93, respectively.

  As shown in FIG. 11, the emboss mark 101 in the ID area of the DVD-RAM disc is formed at a position offset by 1/2 track from the center of the data track composed of lands and grooves. As shown in FIG. 13A, the differential RF signal at is a signal offset upward and downward with respect to the RF signal in the data area. By detecting this offset, the ID area can be detected. In the example of FIG. 11, the differential RF signal is offset to the upper side in the first half of the ID area and to the lower side in the second half, but the reverse case also exists. In the inline circuit of FIG. 9, as shown in FIG. 10A, the input signal of the inline circuit is such that the entire ID area is offset above the data area. This is because the inline circuit inputs not the differential RF signal but the sum of the output signals of the four light receiving elements of the optical pickup.

12, the comparators 90 and 91 detect the upper and lower offsets by comparing the waveforms shown in FIG. 13A with the upper threshold value 88 and the lower threshold value 89, respectively. The signals detected in this way are the signals shown in FIGS. 13B and 13C. The signals generated by combining and shaping these signals are shown in FIG. 13D. It is shown.
Japanese Patent Laying-Open No. 2003-511119 (page 4, FIG. 30, FIG. 31)

  By the way, in recent years, in the optical disk reproducing apparatus, the cost reduction is rapidly progressing, and it is an urgent task to rationalize the circuit correspondingly.

  Among these, since it is difficult for the inline circuit to incorporate the coupling capacitor in the LSI, it is necessary to use the capacitor as an external component. As a result, the number of LSI terminals increases, and inline control is performed. To realize this, a circuit for generating a dedicated timing signal (switching signal) such as an ID area determination signal is separately required, which causes a cost increase for DVD-RAM reproduction.

  As a countermeasure, it is possible to omit the coupling capacitor by performing AD conversion on the reproduction signal of the optical disk and then inputting it to a high-pass filter having a cutoff frequency of 100 Hz. The input dynamic range is large because it includes fluctuations, and an AD converter that performs AD conversion of the input dynamic range requires high performance. For this reason, there has been a problem that the cost increases.

  The present invention has been made in order to solve the above-described problems of the prior art, and eliminates the need for two external capacitors and a circuit for generating a switching signal thereof in the in-line circuit corresponding to the DVD-RAM reproduction. Another object of the present invention is to provide an information reproducing apparatus capable of supporting DVD-RAM reproduction at low cost, an inline circuit thereof, and a method for mounting the inline circuit of the information reproducing apparatus.

  In order to solve this problem, an inline circuit of an information reproducing apparatus according to claim 1 of the present invention includes a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium, and data of the track A circuit for eliminating a difference from a DC offset of an RF signal reproduced from a region, a high-pass filter to which an RF signal reproduced from the information recording medium is input, and an AD converter to which an output of the high-pass filter is input And a lag reed filter to which the output of the AD converter is input.

  The inline circuit of the information reproducing apparatus according to claim 2 of the present invention is the inline circuit of the information reproducing apparatus according to claim 1, wherein the information recording medium is a DVD-RAM disk, and the high-pass filter is the DVD. It has a time constant sufficiently short with respect to the duration of the address area in the reproduction signal of the RAM disk.

  The inline circuit of the information reproducing apparatus according to claim 3 of the present invention is the inline circuit of the information reproducing apparatus according to claim 2, wherein the time constant of the high-pass filter is an address area in the reproduction signal of the DVD-RAM disk. It is characterized by being 10% or less of the continuation time.

  An inline circuit of an information reproducing apparatus according to claim 4 of the present invention is the inline circuit of information reproducing apparatus according to claim 1, wherein the high-pass filter includes a resistor and a capacitor, and the capacitor can be built in an integrated circuit. It has a characteristic capacitance value.

  The inline circuit of the information reproducing apparatus according to claim 5 of the present invention is the inline circuit of the information reproducing apparatus according to claim 1, wherein the lag lead filter has a low frequency characteristic of gain at the first corner frequency. The band-side flat characteristic is changed to the first-order integral characteristic, and the first-order integral characteristic is changed to the high-band-side flat characteristic at the second corner frequency. The second corner frequency is a cutoff frequency at which the gain frequency characteristic of the high-pass filter changes from a first-order differential characteristic to a flat characteristic. It is characterized by having substantially the same frequency.

  An inline circuit for an information reproducing apparatus according to a sixth aspect of the present invention is the inline circuit for an information reproducing apparatus according to the first aspect, wherein the absolute value of the slope of the gain frequency characteristic in the first-order differential characteristic of the high-pass filter is The absolute value of the slope of the frequency characteristic of the gain in the first-order integration characteristic of the lag-lead filter is substantially the same.

  The inline circuit of the information reproducing apparatus according to claim 7 of the present invention is the inline circuit of the information reproducing apparatus according to claim 1, wherein the time constant of the high-pass filter has a low frequency characteristic of the gain of the lag reed filter. The frequency component of the RF signal at the first corner frequency, which is a frequency that changes from the band-side flat characteristic to the first-order integral characteristic, is set to have an amplitude equal to or greater than 1 LSB (Least Significant Bit) of the AD converter. It is characterized by this.

  An inline circuit of an information reproducing apparatus according to claim 8 of the present invention is the inline circuit of information reproducing apparatus according to claim 1, wherein the optical disk is a DVD-RAM disk, the high-pass filter, and the lag lead filter. The frequency characteristics are changed according to the reproduction linear velocity of the DVD-RAM disc.

 An information reproducing apparatus according to claim 9 of the present invention is the inline circuit of the information reproducing apparatus according to claim 1, wherein the optical disk is a DVD-RAM disk, and the AD converter has a sampling frequency of 2 fmax or more. It is characterized by being set. However, fmax = (1 / T) × (N / 6), T = 1 / (29 Mbps) (29 Mbps is the channel bit rate of the DVD-RAM), N is the reproduction speed of the DVD-RAM (N is “1”) "A positive number greater than or equal to").

  An information reproducing apparatus according to claim 10 of the present invention includes a high-pass filter to which an RF signal reproduced from an information recording medium is input, an AD converter to which an output of the high-pass filter is input, and an output of the AD converter , And a demodulator to which the output of the lag lead filter is input, the demodulator having a DC level fluctuation of an RF signal whose low-frequency component is restored by the lag lead filter And an address area in the RF signal is detected.

  An information reproducing apparatus according to claim 11 of the present invention is the information reproducing apparatus according to claim 10, wherein the high-pass filter, the AD converter, the lag-lead filter, and the demodulator are built in the same integrated circuit. It is characterized by that.

  According to a twelfth aspect of the present invention, there is provided an information reproducing apparatus comprising: a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium; and a direct current of an RF signal reproduced from a data area of the track. A method for mounting an inline circuit that eliminates a difference from an offset, wherein a cutoff frequency is a frequency at which a frequency characteristic of a high-pass filter that filters the RF signal as an analog signal changes from a first-order differential characteristic to a flat characteristic Is set to a frequency higher than the target cutoff frequency of the inline circuit, and the frequency characteristic of the lag reed filter that filters the signal after the output signal of the high-pass filter is converted to a digital signal by the AD converter. The first-order integral characteristic substantially cancels the first-order differential characteristic of the high-pass filter. By setting the cut-off frequency in the overall characteristics of the filter and the lag-lead filter so as to substantially match the target cut-off frequency, the time constant of the high-pass filter is reduced, and the high-pass filter is integrated into an integrated circuit. It can be built in.

  According to a thirteenth aspect of the present invention, there is provided a method for mounting an inline circuit in an information reproducing apparatus, wherein a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium and a data area of the track are reproduced. In-line circuit mounting method that eliminates a difference from a direct current offset of an RF signal that has been generated, and the frequency characteristic of a high-pass filter that filters the RF signal as an analog signal changes from a first-order differential characteristic to a flat characteristic. A lag that filters the signal after the cutoff frequency, which is the frequency, is set to a frequency higher than the target cutoff frequency of the inline circuit and the output signal of the high-pass filter is converted to a digital signal by the AD converter. This is the frequency at which the frequency characteristics of the lead filter change from flat characteristics on the low frequency side to first-order integral characteristics. The first corner frequency is set to substantially coincide with the target cutoff frequency, and the frequency characteristic of the lag-lead filter is a frequency at which the frequency characteristic of the lag reed filter changes from the primary integration characteristic to a flat characteristic on the high frequency side. 2 is set so that the corner frequency substantially coincides with the cut-off frequency of the high-pass filter, and the slope of gain decrease due to the first-order integral characteristic of the lag-lead filter and the slope of gain increase due to the first-order differential characteristic of the high-pass filter. Are set so as to have a frequency characteristic that substantially cancels the first-order integral characteristic and the first-order differential characteristic, and the sampling frequency of the AD converter is set to 2 fmax or more. The frequency component of the RF signal at the corner frequency of 1 is greater than 1 LSB (Least Significant Bit) of the AD converter. By setting the time constant of the high-pass filter so as to have a width, the time constant of the high-pass filter is reduced, and the high-pass filter can be built in an integrated circuit. However, fmax = (1 / T) × (N / 6), T = 1 / (29 Mbps) (29 Mbps is the channel bit rate of the DVD-RAM), N is the reproduction speed of the DVD-RAM (N is “1”) "A positive number greater than or equal to").

  According to the first aspect of the present invention, the DC offset of the RF signal reproduced from the address area of the track formed on the information recording medium and the DC offset of the RF signal reproduced from the data area of the track are recorded. A high-pass filter to which an RF signal reproduced from the information recording medium is input, an AD converter to which the output of the high-pass filter is input, and an output of the AD converter are input to the circuit The lag reed filter has a configuration that eliminates the need for switching the coupling capacitor and reduces its capacity, so that a high-pass filter can be built in the integrated circuit without the need for an external capacitor, Significant cost reductions are realized by eliminating the need for timing signals for switching control. It is an effect is obtained that can be.

  According to a second aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the information recording medium is a DVD-RAM disk, and the high-pass filter is a reproduction signal of the DVD-RAM disk. Since the time constant is sufficiently short with respect to the duration of the address area, the DC component of the reproduction signal can be more effectively suppressed.

  According to a third aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the second aspect, the time constant of the high-pass filter is 10% or less of the duration of the address area in the reproduction signal of the DVD-RAM disk. Therefore, the effect of suppressing the DC component can be maintained even if the reproduction linear velocity changes due to the access operation during CLV reproduction.

  According to a fourth aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the high-pass filter is composed of a resistor and a capacitor, and the capacitor has a capacitance value that can be built in an integrated circuit. As a result, the entire in-line circuit including the high-pass filter can be mounted on the integrated circuit, eliminating the need for an external capacitor, thereby increasing the number of terminals of the integrated circuit without increasing the cost. As a result, the cost can be reduced by increasing the number of circuits that can be mounted.

  According to a fifth aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the lag lead filter has a frequency characteristic of a gain that is first order from a low-frequency flat characteristic at a first corner frequency. It changes to an integral characteristic, and changes from the first-order integral characteristic to a high-frequency flat characteristic at a second corner frequency. The first corner frequency is a signal whose group delay characteristic of the signal after low-frequency restoration is data. A frequency that does not affect reproduction, and the second corner frequency is a frequency that is substantially equal to a cutoff frequency at which the frequency characteristic of the gain of the high-pass filter changes from a first-order differential characteristic to a flat characteristic. As a result, the low-frequency component can be restored after AD conversion, and the effect of improving the group delay characteristic of the RF signal can be obtained.

  According to the sixth aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the absolute value of the slope of the frequency characteristic of the gain in the first-order differential characteristic of the high-pass filter and the 1 of the lag-lead filter Since the absolute value of the slope of the frequency characteristic of the gain in the second-order integral characteristic is substantially the same, the first-order differential characteristic of the high-pass filter and the first-order integral characteristic of the lag-lead filter can be offset, so that the cutoff of the high-pass filter The frequency can be moved to the high frequency side, and the effect that the time constant of the high-pass filter can be kept small can be obtained.

  According to a seventh aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the time constant of the high-pass filter is such that the frequency characteristic of the gain of the lag lead filter is first order from the low-frequency flat characteristic. Since the frequency component of the RF signal at the first corner frequency, which is a frequency that changes to the integral characteristic, is set to have an amplitude equal to or greater than 1 LSB (Least Significant Bit) of the AD converter, the optical reproduction signal After eliminating the DC offset between the ID area and the data area, the lag lead filter can recover the DC component from the remaining RF component by setting the time constant as described above.

  According to an eighth aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the optical disc is a DVD-RAM disc, and the frequency characteristics of the high-pass filter and the lag lead filter are the DVD-RAM disc. -Since the configuration is changed according to the reproduction linear velocity of the RAM disk, the same effect as that in the case of reproducing at the standard reproduction speed can be obtained for various reproduction double speeds.

  According to a ninth aspect of the present invention, in the inline circuit of the information reproducing apparatus according to the first aspect, the optical disk is a DVD-RAM disk, and the AD converter has a sampling frequency set to 2 fmax or more. Therefore, there is an effect that the optical reproduction signal after passing through the high-pass filter can be converted into a digital signal without generating a aliasing component.

  According to the tenth aspect of the present invention, a high pass filter to which an RF signal reproduced from an information recording medium is input, an AD converter to which an output of the high pass filter is input, and an output of the AD converter are input. A lag reed filter; and a demodulator to which the output of the lag reed filter is input. The demodulator detects a DC level variation of the RF signal whose low frequency component is restored by the lag reed filter. Since the address area in the RF signal is detected, the address area can be detected without providing a dedicated circuit, and the address area can be detected stably regardless of pickup variations. The effect that cost reduction is realizable is acquired.

  According to the invention of claim 11, in the information reproducing apparatus of claim 10, the high-pass filter, the AD converter, the lag lead filter, and the demodulator are built in the same integrated circuit. As a result, an effect that a significant cost reduction can be realized is obtained.

  According to the invention described in claim 12, the difference between the DC offset of the RF signal reproduced from the address area of the track formed on the information recording medium and the DC offset of the RF signal reproduced from the data area of the track. A cut-off frequency, which is a frequency at which the frequency characteristic of a high-pass filter that filters the RF signal as an analog signal changes from a first-order differential characteristic to a flat characteristic, The first-order integration characteristic in the frequency characteristic of a lag reed filter that sets a frequency higher than the target cut-off frequency and filters the signal after the output signal of the high-pass filter is converted into a digital signal by an AD converter Substantially cancels the first-order differential characteristic of the high-pass filter. The time constant of the high-pass filter can be reduced by setting the cut-off frequency in the overall characteristics with the lead filter to substantially match the target cut-off frequency, and the high-pass filter can be built in an integrated circuit. As a result, the cutoff frequency of the high-pass filter can be moved to a high frequency, the time constant of the high-pass filter can be kept small, and the high-pass filter can be built in the integrated circuit without using an external capacitor.

  According to the invention of claim 13, the difference between the DC offset of the RF signal reproduced from the address area of the track formed on the information recording medium and the DC offset of the RF signal reproduced from the data area of the track. A cut-off frequency, which is a frequency at which the frequency characteristic of a high-pass filter that filters the RF signal as an analog signal changes from a first-order differential characteristic to a flat characteristic, The frequency characteristic of the lag lead filter that filters the signal after the output signal of the high-pass filter is converted to a digital signal by the AD converter is set to a frequency lower than the target cutoff frequency of The first corner frequency, which is a frequency changing from the flat characteristic to the first-order integral characteristic, is set as the target level. A cutoff frequency of the high-pass filter is set to a second corner frequency which is set so as to substantially match a to-off frequency and the frequency characteristic of the lag-lead filter changes from the first-order integral characteristic to a flat characteristic on the high band side. It is set so that it substantially matches the frequency, and the slope of the gain decrease due to the first-order integral characteristic of the lag-lead filter and the slope of the gain increase due to the first-order differential characteristic of the high-pass filter are made substantially the same value. A frequency characteristic of the RF signal at the first corner frequency is set such that the frequency characteristic substantially cancels the second-order integral characteristic and the first-order differential characteristic, and the sampling frequency of the AD converter is set to 2 fmax or more. Of the high-pass filter so that the amplitude is equal to or greater than 1 LSB (Least Significant Bit) of the AD converter. By setting the number, the time constant of the high-pass filter is reduced, and the high-pass filter can be built in the integrated circuit, so that the cutoff frequency of the high-pass filter can be moved to a high frequency, and the time constant of the high-pass filter is reduced. A high-pass filter can be built in an integrated circuit without an external capacitor, and the optical reproduction signal after passing through the high-pass filter can be converted into a digital signal without generating a aliasing component. The read filter has an effect that the DC component can be recovered from the RF component remaining by setting the time constant as described above.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
(Embodiment 1)
FIG. 1 is a block diagram of an optical disk reproducing apparatus according to Embodiment 1 of the present invention, and particularly shows an inline circuit thereof. 1A, reference numeral 1 denotes an input amplifier that amplifies an optical reproduction signal (RF signal) that is a sum signal of output signals of all the photodetectors A, B, C, and D of the optical pickup 300 of FIG. Is a coupling capacitor provided after the input amplifier 1, 3 is a resistor constituting the high-pass filter 10 together with the capacitor 2, 4 is a buffer amplifier that amplifies the output signal of the high-pass filter 10, and 5 is an output signal of the buffer amplifier 4 An AD converter for conversion, 6 is a lag lead filter that gives lag lead characteristics to the output signal of the AD converter 5, and 7 is a demodulator that performs demodulation by binarization on the output signal of the lag lead filter 6. The signal processing circuit 500 shown in FIG. An in-line circuit 400 is configured by circuit elements from the subsequent stage of the input amplifier 1 to the previous stage of the demodulator 7, that is, the high-pass filter 10, the buffer amplifier 4, the AD converter 5, and the lag lead filter 6.

  Further, as shown in FIG. 1B, at least one of the capacitor 2 or the resistor 3 is a variable capacitor or variable resistor, and the frequency of the high-pass filter 10 is controlled by controlling at least one of the capacitance value or the resistance value by the system controller 600. The characteristics may be set, and the frequency characteristics of the lag lead filter 6 may be set.

  FIG. 1C shows a configuration example of the capacitor C1 and the resistor R1 of FIG. 1B, and a switch is provided between one end of three capacitors C1a, C1b, and C1c connected in parallel with each other and an output node of the input amplifier 1. SCa, SCb, SCc are inserted, and switches SRa, SRb, SRc are inserted between one end of three resistors R1a, R1b, R1c connected in parallel to the Vref node, and switches SCa, SCb, SCc and The switches SRa, SRb, SRc are configured to be turned on / off by the system controller 600.

  FIG. 2 shows the frequency characteristics of the high-pass filter 10 and the lag lead filter 6 and the target characteristics as a total characteristic of these.

  In FIG. 2, a represents an example of the characteristics of the high-pass filter 10, and the first-order differential characteristics a <b> 1 are 10 KHz or less and flat characteristics (proportional characteristics) are 10 KHz or more. Further, b represents an example of the characteristics of the lag reed filter 6, which shows the first-order integral characteristic b1 in the region where the cut-off frequency of the high-pass filter 10 is 10 KHz or less, and 100 Hz or less is the low-frequency flat characteristic (proportional characteristic) b2, 10 KHz. In the above, the high-frequency side flat characteristic (proportional characteristic) b3 is obtained. The signals that have passed through the high-pass filter 10 and the lag-lead filter 6 are canceled out by the first-order differential characteristic a1 and the first-order integration characteristic b1, and the flat characteristic expands to the low frequency side. Become. The frequency characteristic of the target characteristic c is equivalent to a high-pass filter with a cut-off frequency of 100 Hz, and does not affect the group delay characteristic of the RF signal component.

  In order to make this possible, the inline circuit 400 is mounted as follows. That is, as shown in FIG. 2, the second corner frequency fc2 of the lag reed filter 6 and the cut-off frequency of the high-pass filter 10 are both set to 10 KHz, and the gain frequency of the primary integration characteristic b1 of the lag reed filter 6 is set. By setting the negative slope value of the characteristic and the positive slope value of the gain frequency characteristic of the primary differential characteristic a1 of the high-pass filter 10 to coincide with each other, the primary integral characteristic b1 and the primary differential characteristic a1 are set. And the target characteristic, that is, the frequency characteristic of the high-pass filter 10 and the lag reed filter 6 is set to a flat proportional characteristic at 10 KHz or less, and the first corner frequency fc1 of the lag reed filter 6 is set to 100 Hz. By setting the flat characteristic b2 below 100 Hz, the target characteristic becomes the first-order differential characteristic below 100 Hz. Unishi to have. Note that 100 Hz, which is the value of the first corner frequency fc1, is a frequency at which the group delay characteristic of the signal after the low frequency restoration does not affect the data reproduction.

Hereinafter, the inline circuit 400 and the mounting method thereof will be described in more detail.
FIG. 3 shows signal waveforms at various parts of the optical disk reproducing apparatus of FIG. 1. FIG. 3 (a) shows a reproduction signal inputted to the input amplifier 1, and the portion where the DC level is high in FIG. (Address area) and others are data areas. 3B shows a signal after passing through the high-pass filter 10, FIG. 3C shows a signal in which the low-frequency component has been restored after passing through the lag lead filter 6, and FIG. 3D shows an ID detection signal.

  Now, during reproduction of a DVD-RAM, a reproduction signal (see FIG. 3A) similar to that in FIG.

  The reproduced signal is amplified by the input amplifier 1 in FIG. 1A, the low frequency is suppressed by the high pass filter 10 to eliminate the DC offset in the ID region, amplified by the buffer amplifier 4, and then the AD converter 5 Is converted into a multi-bit digital signal, the low-frequency component suppressed by the high-pass filter 10 is restored by the lag lead filter 6, the multi-bit digital signal is binarized by the demodulator 7, and the original signal is generated in the subsequent stage. Signal processing is performed to reproduce information recorded on the DVD-RAM.

  The high-pass filter 10 and the lag lead filter 6 realize a high-pass filter characteristic in total, and remove the DC component in the optical reproduction signal without affecting the group delay characteristic of the RF signal.

  The total cut-off frequency of the high-pass filter characteristic is determined by the first corner frequency fc1 of the lag-lead filter 6, and the first-order differential characteristic a1 of the high-pass filter 10 at a frequency higher than the first corner frequency fc1. Is canceled out by the first-order integral characteristic b1 of the lag reed filter 6 in a region higher than the first corner frequency fc1 to obtain a flat proportional characteristic. In order to enable this, as described above, the cutoff frequency of the high-pass filter 10 and the second corner frequency fc2 of the lag lead filter 6 are matched, and the negative slope value of the first-order integral characteristic b1 is The value of the positive slope of the primary differential characteristic a1 is matched.

  In the first embodiment, a simple high-pass filter 10 removes DC level fluctuations accompanying ID region reproduction to obtain the waveform shown in FIG. Compress to fit within range. Thereby, AD conversion is enabled for both the data area and the ID area.

  For this purpose, the setting of the cutoff frequency of the high-pass filter 10 is important, but the duration of the ID region is about 75 μsec at a reproduction speed of the channel bit rate of 29 Mbps, and the time constant of the high-pass filter is sufficient for this. Must be set to a small value. For example, when the cut-off frequency is 10 KHz as shown in FIG. 2a, the time constant is 16 μsec, which is 1/5 of the duration of the ID area, which is sufficient for suppressing the DC component. It is believed that there is.

  In addition, when the reproduction double speed (N times the standard reproduction speed) is increased, the duration of the ID region is also shortened, so that it is necessary to shift the cutoff frequency of the high-pass filter 10 to the higher frequency side. Accordingly, it is necessary to shift the second corner frequency of the lag reed filter 6 to a higher frequency side. These shifts can be realized by giving a control signal from the system controller 600 to the high-pass filter 10 and the lag lead filter 6 as shown in FIG.

  Further, in order to suppress the DC component with respect to fluctuations in the reproduction linear velocity accompanying the access operation at the time of CLV reproduction, the time constant of the high-pass filter 10 is set to continue the ID area in the reproduction signal of the DVD-RAM. It is necessary to set the time to be sufficiently shorter than the time, for example, 10% or less.

  However, if the DC component is suppressed, the reproduction signal is affected by the phase shift by the high-pass filter 10 and the group delay characteristic is deteriorated. Therefore, the low-frequency component is restored by the lag lead filter 6 after AD conversion. As a result, the deterioration of the group delay characteristic can be suppressed, and the signal shown in FIG. 3C can be obtained.

  That is, as shown in the lag lead characteristic b of FIG. 2, the lag lead filter 6 having a cutoff frequency at 100 Hz (first corner frequency fc1) and 10 KHz (second corner frequency fc2) is used in a low frequency region. By increasing the gain, the signal passing through the high-pass filter 10 and the lag lead filter 6 is equivalent to passing through a high-pass filter having a cutoff frequency of 100 Hz as shown in FIG.

  With such a high-pass filter with a cutoff frequency of 100 Hz, the influence of the phase rotation on the RF band can be kept at a sufficiently low level.

  Further, as described above, by using the lag reed filter 6 and the high pass filter 10, the same high frequency pass characteristic with a cutoff frequency of 100 Hz as in the conventional example is realized. In order to compensate for the component gain, the cut-off frequency of the high-pass filter 10 can be set as high as 10 KHz, whereby the time constant of the high-pass filter 10 can be kept small.

  For this reason, the capacity of the capacitor 2 constituting the high-pass filter 10 can be suppressed, whereby the entire inline circuit 400 can be built in the LSI without the capacitor 2 being externally attached.

  Here, it is examined whether or not the low-frequency component removed by the high-pass filter 10 can actually be restored after AD conversion.

  If the frequency characteristics of the high-pass filter 10 are for a single frequency, as shown in FIG. 2, a 100 Hz signal is 1/100 of a 10 KHz signal, and therefore the AD converter 5 has a 6-bit resolution, for example. The resolution becomes 1/64 or less, and becomes completely zero, so that the low frequency recovery by the lag lead filter 6 is impossible. However, in the case of the reproduction signal of the optical disk, as shown in FIG. 4, if the RF component exists and the level is set so as to exceed the resolution of the AD converter, this effectively works as a dither, Low frequency components of 100 Hz or less also remain as information dispersed between sampling data. The lag-lead filter 6 acts as an integrator for the dispersed information, and restores the information to restore the low-frequency component.

  In order to realize the restoration of the low-frequency component, the high-pass filter 10 is configured so that the frequency component of the RF signal at the first corner frequency fc1 (= 100 Hz) has an amplitude of 1 LSB or more of the AD converter 5. It is necessary to set a constant.

  That is, if the cut-off frequency of the high-pass filter 10 is set too high, the attenuation in the low band increases, so this needs to be set with care.

Furthermore, the setting of the sampling frequency of the AD converter 5 is also important, and it is necessary to set it to 2 fmax or more.
By setting the sampling frequency to 2 fmax or more in this way, it is possible to prevent the aliasing component from being generated when AD conversion is performed on the optical reproduction signal after the DC fluctuation component is removed by the high-pass filter 10.
here,
fmax = (1 / T) × (N / 6) (1)
And
T = 1 / (29 Mbps) (29 Mbps is the channel bit rate of DVD-RAM),
N is the playback speed of DVD-RAM (N is a positive number greater than “1”)
“6” in the equation (1) is derived from the fact that three or more “1” s and “0” s recorded in the DVD-RAM continue as shown in FIG.

  The lag lead filter 6 is a combination of a low-pass filter and a high-pass filter. As shown in FIG. 6, the lag-lead filter 6 is completely composed of multipliers 6a and 6b, adders 6c and 6d, and a delay unit 6e. Since it can be configured as a digital filter, a cut-off frequency of 100 Hz can be easily realized and can be configured at low cost.

Next, data reproduction will be described.
In the conventional example, since the signal subjected to AD conversion is a signal from which the DC level fluctuation has been removed, it is necessary to detect the ID region by a completely different circuit, but the DC level of the reproduction signal 3 can be restored as shown in FIG. 3C, the ID detection level shown in FIG. 3C can be set to detect the DC level fluctuation.

  The ID detection level may be obtained by experimentally determining and using an intermediate value between the values of the upper envelope in the waveform data area and the upper envelope in the ID area shown in FIG. 3C. In particular, the value of the upper envelope in the ID area is Since it is almost known, a level lower than this value may be used as the ID detection level.

  FIG. 3D shows an ID detection result. For example, by switching the binarized slice level according to this signal, the reproduction signal in both the data area and the ID area is binarized to obtain data. I can do it.

  FIG. 7 is a block diagram of the optical disk reproducing apparatus according to Embodiment 1 of the present invention that enables the above-described data reproducing operation. In FIG. 7, the same reference numerals as those in FIG. 7a is a demodulator body having the same function as the demodulator 7 in FIG. 1, 8 is a comparator for comparing the output signal of the lag-lead filter 6 and a threshold, 9 is a threshold generator for generating this threshold, and 7 is these The demodulator includes a demodulator body 7a, a comparator 8, and a threshold generator 9. The threshold generator 9 is set with a threshold obtained experimentally as described above.

  In FIG. 7, the comparator 8 compares the output signal of the lag lead filter 6 with a threshold value. The RF signal in which the low frequency component is restored by the lag lead filter 6 is as shown in FIG. 3C, and by setting a threshold value to the level shown as the ID detection level in FIG. 3C, FIG. As shown in d), it is possible to obtain an ID region detection signal that becomes “H” level in a period corresponding to the ID region.

  This ID area detection signal can be generated without the need for a large-scale dedicated circuit as shown in FIG. 9 of the conventional example, and all the optical detections of the optical pickup 300 are input to the input amplifier. This is the sum signal of the output signals of the detectors A, B, C, and D, and the push-pull signal of the photodetector does not use this signal. The ID area can be detected without being affected.

  That is, when the push-pull signal of the photodetector is used in the detection of the ID area, the offset amount of the differential signal in the ID area is increased by the upper side and the lower side due to the optical axis deviation of the pickup, the light receiving element position deviation, etc. In this case, since either one of the ID areas cannot be detected, a problem may occur in the inline processing. In the first embodiment using a sum signal, the ID area Since the level of the upper envelope of the RF signal in FIG. 1 is a reflection level from the mirror portion in the ID region, that is, the portion without the emboss mark 101, the ID is derived from the mechanical mounting accuracy of the components of such a pickup. It becomes possible to eliminate the problem that the inline processing becomes defective because the area cannot be detected.

  Also in this optical disk reproducing apparatus, when the DVD-RAM disk performs double speed reproduction, it is necessary to change the characteristics of the high-pass filter 10 and the lag lead filter 6 according to the reproduction double speed. This can be dealt with by changing the time constant of the high-pass filter 10, the multiplication coefficient of the lag-lead filter 6, and the like under the control of the system controller 600 as in the above-described inline circuit.

  Further, the second corner frequency fc2 (= 10 KHz) of the lag lead filter 6 and the cut-off frequency of the high-pass filter 10 exhibiting the first-order differential characteristics are made to coincide with each other, but these do not coincide completely. For example, an error of 10% or less is acceptable.

  Further, the first-order integral characteristic of the lag lead filter 6 and the first-order differential characteristic of the high-pass filter 10 are canceled out. However, this may not be completely canceled out, and the total of the lag-lead filter 6 and the high-pass filter 10 is not necessary. Some of the first-order integral characteristics, first-order differential characteristics, or both of them may remain in the above characteristics. For example, a residual amount of 10% or less with respect to the proportional characteristics is acceptable.

  Further, the description has been given on the assumption that the capacitor 2 constituting the high-pass filter 10 can be mounted on the LSI without providing an external component. In addition to the entire in-line circuit 400, the LSI includes the demodulation circuit 7 and further a signal processing circuit in the subsequent stage. May also be installed.

Further, FIG. 1B shows the capacitor 2 and the resistor 3 being variable, but either the capacitor 2 or the resistor 3 may be variable, and these configurations are shown in FIG. It is not limited.
Further, in the case where double-speed reproduction of the DVD-RAM disc is not performed, these may be fixed.

  The threshold generator 9 of the demodulator 7 presets the experimentally obtained threshold, but this can be set by providing a circuit for determining the threshold in real time from the waveform of FIG. Is also possible.

  Furthermore, the case where the information reproducing apparatus is applied to an optical disk reproducing apparatus compatible with a DVD-RAM disk has been shown. However, as long as the information reproducing apparatus includes a reproducing function of a DVD-RAM disk, it can also reproduce an optical disk other than a DVD-RAM disk. The present invention is also applicable to the optical disc playback device and the optical disc recording / playback device.

  Thus, according to the first embodiment, the input amplifier to which the RF signal reproduced from the optical disc is input, the high-pass filter to which the output of the input amplifier is input, and the output of the high-pass filter are input. Since it is configured to include an AD converter, a lag lead filter to which the output of the AD converter is input, and a demodulator that digitally processes the output of the lag lead filter and demodulates it as a binary signal, a coupling capacitor Switching is unnecessary, and the capacity can be reduced, so that it can be built in LSI, and the timing signal for switching control of the coupling capacitor is not required at all. The effect that it can be realized is obtained.

  Also, a high-pass filter to which an RF signal reproduced from an optical disk is input, an AD converter to which the output of the high-pass filter is input, a lag lead filter to which the output of the AD converter is input, and an output thereof are input. A demodulator, and the demodulator is configured to detect the ID region by detecting a DC level variation of the RF signal whose low-frequency component is restored by the lag-lead filter. Therefore, it is possible to suppress an increase in cost due to the provision of a dedicated circuit. Further, it becomes possible to detect the ID area without using the push-pull signal of the optical detector of the pickup, and the effect that the ID area can be detected stably without depending on the variation of the pickup can be obtained.

  As described above, according to the present invention, an optical disk reproducing apparatus that realizes a more stable DVD-RAM reproducing function at a low cost can be obtained, which is suitable for use in such an optical disk reproducing apparatus.

1 is a block diagram showing an optical disk reproducing device according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing another configuration example of the optical disc reproducing apparatus according to Embodiment 1 of the present invention. FIG. 1B is a circuit diagram showing a configuration in which the resistance and the capacitance value of the capacitor constituting the high-pass filter of FIG. 1B are variable. Bode plot of filter frequency characteristics FIG. 2 is a signal waveform diagram showing the operation of FIG. 1 and showing a reproduction signal input to an input amplifier. FIG. 2 is a signal waveform diagram showing the operation of FIG. 1 and shows a signal after passing through a high-pass filter. FIG. 2 is a signal waveform diagram illustrating the operation of FIG. 1, and is a diagram illustrating a signal that has passed through a lag lead filter and restored a low-frequency component. FIG. 2 is a signal waveform diagram illustrating the operation of FIG. 1 and illustrating an ID detection signal. Signal waveform diagram of optical reproduction signal with RF component superimposed The figure which shows the derivation | leading-out principle of the calculation formula of the sampling rate of AD converter required in order to revive a low frequency component after passing a lag reed filter Diagram showing the basic configuration of the lag reed filter 1 is a block diagram showing a configuration example of a demodulator of an optical disk reproducing device according to Embodiment 1 of the present invention. The block diagram which shows the whole structure of the conventional optical disk reproducing | regenerating apparatus Circuit diagram showing configuration of inline circuit of conventional optical disk reproducing apparatus It is a signal waveform diagram of an in-line circuit of a conventional optical disc playback apparatus, and shows an input signal of an input amplifier FIG. 7 is a signal waveform diagram of an inline circuit of a conventional optical disc playback apparatus, and shows an ID region discrimination signal It is a signal waveform diagram of the inline circuit of the conventional optical disk reproducing apparatus, and shows a pull-in signal It is a signal waveform diagram of the inline circuit of the conventional optical disk reproducing device, and shows the input signal of the AD converter The figure which shows the structure of ID part of a DVD-RAM disk The figure which shows the structure of the conventional ID area | region discrimination | determination signal generation circuit. Signal waveform diagram showing differential RF signal of conventional ID region discrimination signal generation circuit and its two threshold values Signal waveform diagram showing a state in which the offset of the differential RF signal in the ID region of the conventional ID region discrimination signal generation circuit is detected Signal waveform diagram showing a state in which the offset of the differential RF signal in the ID region of the conventional ID region discrimination signal generation circuit is detected Signal waveform diagram showing ID area discrimination signal detected by a conventional ID area discrimination signal generation circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input amplifier 2 Coupling capacitor 3 Resistance 4 Buffer amplifier 5 AD converter 6 Lag lead filter 7 Demodulator 7a Demodulator main body 8 Comparator 9 Threshold generator 10 High pass filter 400 In-line circuit 600 System controller fc1 1st corner frequency fc2 2nd Corner frequency f The cutoff frequency of the target characteristic

Claims (13)

A circuit for eliminating a difference between a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium and a DC offset of an RF signal reproduced from a data area of the track,
A high-pass filter to which an RF signal reproduced from the information recording medium is input;
An AD converter to which the output of the high-pass filter is input;
A lag reed filter to which the output of the AD converter is input,
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The information recording medium is a DVD-RAM disk;
The high-pass filter has a time constant that is sufficiently short with respect to the duration of the address area in the reproduction signal of the DVD-RAM disc.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 2,
The time constant of the high-pass filter is 10% or less of the duration of the address area in the reproduction signal of the DVD-RAM disc.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The high pass filter includes a resistor and a capacitor,
The capacitor has a capacitance value that can be incorporated in an integrated circuit.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The lag-lead filter has a gain frequency characteristic that changes from a low-frequency flat characteristic to a first-order integral characteristic at a first corner frequency, and changes from the first-order integral characteristic to a high-frequency flat characteristic at a second corner frequency. Change,
The first corner frequency is a frequency at which the group delay characteristic of the signal after the low frequency restoration does not affect the data reproduction,
The second corner frequency is a frequency that is substantially equal to a cutoff frequency at which the frequency characteristic of the gain of the high-pass filter changes from a first-order differential characteristic to a flat characteristic.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The absolute value of the slope of the frequency characteristic of the gain in the first-order differential characteristic of the high-pass filter and the absolute value of the slope of the frequency characteristic of the gain in the first-order integral characteristic of the lag-lead filter are substantially the same.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The time constant of the high-pass filter is such that the frequency component of the RF signal at the first corner frequency, which is a frequency at which the frequency characteristic of the gain of the lag-lead filter changes from a low-frequency flat characteristic to a first-order integral characteristic, It is set to have an amplitude greater than 1LSB (Least Significant Bit) of the converter.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The optical disc is a DVD-RAM disc;
The frequency characteristics of the high-pass filter and the lag lead filter are changed according to the reproduction linear velocity of the DVD-RAM disc.
An in-line circuit for an information reproducing apparatus. In the inline circuit of the information reproducing apparatus according to claim 1,
The optical disc is a DVD-RAM disc;
In the AD converter, the sampling frequency is set to 2 fmax or more.
An in-line circuit for an information reproducing apparatus.
However, fmax = (1 / T) × (N / 6),
T = 1 / (29 Mbps) (29 Mbps is the channel bit rate of DVD-RAM),
N is a reproduction speed of the DVD-RAM (N is a positive number of “1” or more). A high-pass filter to which an RF signal reproduced from an information recording medium is input;
An AD converter to which the output of the high-pass filter is input;
A lag lead filter to which the output of the AD converter is input;
A demodulator to which the output of the lag-lead filter is input,
The demodulator detects a DC level variation of the RF signal whose low-frequency component is restored by the lag-lead filter, and detects an address region in the RF signal.
An information reproducing apparatus characterized by that. The information reproducing apparatus according to claim 10, wherein
The high-pass filter, the AD converter, the lag lead filter, and the demodulator are built in the same integrated circuit.
An information reproducing apparatus characterized by that. An in-line circuit mounting method that eliminates a difference between a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium and a DC offset of an RF signal reproduced from a data area of the track. ,
The cut-off frequency, which is the frequency at which the frequency characteristic of the high-pass filter that filters the RF signal as an analog signal changes from the first derivative characteristic to the flat characteristic, is set to a frequency higher than the target cut-off frequency of the in-line circuit. And
And the first-order differential characteristic of the high-pass filter is substantially canceled by the first-order integral characteristic in the frequency characteristic of the lag-lead filter that filters the signal after the output signal of the high-pass filter is converted into a digital signal by the AD converter, By setting the cutoff frequency in the overall characteristics of the high-pass filter and the lag lead filter so as to substantially match the target cutoff frequency,
The time constant of the high-pass filter is reduced, and the high-pass filter can be built in an integrated circuit.
An inline circuit mounting method for an information reproducing apparatus. An in-line circuit mounting method that eliminates a difference between a DC offset of an RF signal reproduced from an address area of a track formed on an information recording medium and a DC offset of an RF signal reproduced from a data area of the track. ,
The cut-off frequency, which is the frequency at which the frequency characteristic of the high-pass filter that filters the RF signal as an analog signal changes from the first derivative characteristic to the flat characteristic, is set to a frequency higher than the target cut-off frequency of the in-line circuit. And
In addition, the frequency characteristic of the lag lead filter that filters the signal after the output signal of the high-pass filter is converted into a digital signal by the AD converter is a frequency at which the frequency characteristic changes from the flat characteristic on the low band side to the first-order integral characteristic. 1 corner frequency is set to substantially match the target cutoff frequency,
And setting the second corner frequency, which is a frequency at which the frequency characteristic of the lag-lead filter changes from the first-order integral characteristic to the flat characteristic on the high frequency side, to substantially match the cutoff frequency of the high-pass filter,
The slope of the gain decrease due to the first-order integral characteristic of the lag-lead filter and the slope of the gain increase due to the first-order derivative characteristic of the high-pass filter are set to substantially the same value to obtain the first-order integral characteristic and the first-order derivative characteristic Set the frequency characteristics to almost cancel,
And the sampling frequency of the AD converter is set to 2 fmax or more,
And by setting the time constant of the high-pass filter so that the frequency component of the RF signal at the first corner frequency has an amplitude equal to or greater than 1 LSB (Least Significant Bit) of the AD converter,
The time constant of the high-pass filter is reduced, and the high-pass filter can be built in an integrated circuit.
An inline circuit mounting method for an information reproducing apparatus.
However, fmax = (1 / T) × (N / 6),
T = 1 / (29 Mbps) (29 Mbps is the channel bit rate of DVD-RAM),
N is a reproduction speed of the DVD-RAM (N is a positive number of “1” or more).

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