JP2005174472A - Automatic equalizer, automatic equalization method and storage medium storing automatic equalization program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic equalizer which can obtain a good convergence state in a short time and has a good convergence stability.
When a signal x reproduced by a magnetic head 1 is processed by a digital filter 4 and equalized, an adder 7 subtracts an output y of the digital filter 4 from an output signal d of a decoding circuit 5 to generate an error ε. (ε = d−y) is taken out, this error ε is supplied to the adaptive control unit 9, and a combination of tap coefficients T corresponding to each position of the waveform A per head is input from the coefficient memory 10 to the digital filter 4. In the automatic equalizer 15 in which the optimum equalization characteristic is automatically given by the digital filter 4, a time constant filter circuit 8 is provided so as to give a time constant to the error ε and reproduced by the magnetic head 1. The envelope detection circuit 11 detects the level of the signal x, and the application control unit 9 supplies the control signal c to the time constant filter circuit 8 according to the level of the signal x, and is timed according to the level of the signal x. Those to control the filter time constant of the filter circuit 8.
[Selection] Figure 1

Description

  The present invention relates to an equalization means for reproducing a digital signal from a recording medium, and in particular, an automatic equalizer, an automatic equalization method, and a storage storing an automatic equalization program used in the digital reproduction apparatus. It relates to the medium.

  In a digital reproduction device that reproduces information recorded on a recording medium such as a magnetic disk or magnetic tape (in the case of a digital VTR), a signal read from the recording medium is converted into a digital signal, and equalization processing and error correction processing are performed. After that, the information read from the recording medium is reproduced by decoding in the decoding unit.

  Here, as described above, equalization processing and error correction processing are performed in order to reduce errors that occur in a signal when digital data is played back or communicated from a digital playback device. .

  The equalization processing at this time is generally processing for compensating the frequency characteristics based on the amplitude and phase of the reproduction signal, and for this purpose, the digital reproduction apparatus includes a waveform equalizer. An example of this waveform equalizer is a transversal filter.

  By the way, in the case of a digital playback device, the playback signal read from the recording medium is not constant in the state of the recorded signal, the playback system, the frequency characteristics of the communication path, etc. Therefore, the state of the playback signal also varies sequentially. It is a thing.

  Further, the data recorded on this recording medium may change depending on factors such as a change with time and an environmental change. Therefore, it is not possible to expect sufficient equalization if processing is performed uniformly.

  Therefore, by detecting such fluctuations in the reproduction signal and sequentially changing the equalization characteristics of the equalizer accordingly, optimum equalization is always performed and stable reproduction is performed. Therefore, automatic equalizers are widely used.

  Of the fluctuations that occur in the reproduction signal described above, especially in a digital VTR that uses a magnetic tape as a recording medium, the reproduction is caused by a contact state between the rotating magnetic head and the magnetic tape, so-called head contact. There is a variation in the RF signal waveform.

  Thus, the fluctuation of the reproduction RF signal waveform in such a digital VTR will be described with reference to FIG. 6. Here, A in the figure is divided into 180 ° angles with each other in a magnetic reproduction apparatus equipped with a rotating magnetic head. 2 shows an envelope waveform of a reproduction RF signal obtained from one of a pair of magnetic heads installed.

  Then, according to the waveform A in FIG. 6, it can be understood that the level of the reproduction signal appears during the period (one scan period) from the contact start point Pa to the contact end point Pb of the tape and the head.

  By the way, when the equalization process is performed on the reproduction RF signal having the level fluctuation as described above, an automatic equalizer of a system in which the equalizer characteristic is continuously followed during one scan period is general.

  On the other hand, the equalization characteristic is optimized based on the data of the reproduction RF signal only at the pulse timing shown in FIG. B within one scan period shown in the waveform A of FIG. An automatic equalizer of the type is also known as the prior art (see, for example, Patent Document 1).

  Therefore, the automatic equalizer according to the prior art will be described with reference to FIG. 7. In FIG. 7, information recorded on a magnetic tape (not shown) as a recording medium is transferred to a mechanism unit (not shown) of the magnetic reproducing apparatus. It is read by the magnetic head 1 provided, input as a reproduction signal to the reproduction amplifier circuit 2, amplified here, and then sent to the detection characteristic circuit 3.

  This detection characteristic circuit 3 is assumed to be a recording / reproduction device of a system that records and reproduces on a magnetic tape (video tape) using a so-called partial response system, and is therefore a partial response detection characteristic (encoding characteristic) ( 1 + D) frequency characteristics.

  Next, the output signal of the detection characteristic circuit 3 is input to the digital filter 4 and subjected to equalization processing. As the digital filter 4, a transversal filter or the like is used, and the filter characteristic will be described later. It is set adaptively by the adaptive control unit 9, whereby the performance as an automatic equalizer is exhibited.

  The output signal of the digital filter 4 is supplied to a decoding circuit 5, and is discriminated into two data values “1” and “0” by level comparison and decoded (decoded) into a data series at the time of recording. From this, the output signal d is also supplied to an adder 7 that functions as an error detector at the same time.

  Here, the adder 7 subtracts the output y of the digital filter 4 from the output signal d of the decoding circuit 5 to extract an error ε (ε = dy), and supplies the error ε to the adaptive control unit 9. Work.

  At this time, the output x of the detection characteristic circuit 3 is supplied to the adaptive control unit 9 as a reference input, so that the adaptive control unit 9 performs digital filtering in a direction in which the signal power of the error ε converges to the minimum value. The tap coefficient of 4 is changed and updated.

  Thus, the equalization characteristic is set so as to have a frequency characteristic close to the inverse characteristic of the electromagnetic conversion characteristic in magnetic recording / reproduction. As a result, the digital filter 4 and the adaptive control unit 9 use the so-called automatic equalization filter. Is supposed to be configured.

  At this time, a coefficient memory 10 is provided as a tap coefficient storage unit in the path from the adaptive control unit 9 to the digital filter 4, and a memory 12 is provided as a storage unit in the path from the detection characteristic circuit 3 to the adaptive control unit 9. is there.

  On the other hand, a head switching switching pulse SWP is supplied to the input terminal 13, and this is input to the timing generation circuit 14, whereby the timing generation circuit 14 generates a predetermined timing pulse.

  Then, the timing pulse output from the timing generation circuit 14 is supplied to the adaptive control unit 9, the coefficient memory 10, and the memory 12, and as a result, the timing necessary for data calculation processing and data fetching can be obtained. It has become.

  Next, the operation of the automatic equalization filter shown in FIG. 7 will be described with reference to FIG. Here, a waveform A in FIG. 8 shows an envelope waveform of a reproduction RF signal from one of a pair of magnetic heads installed at an angle of 180 ° with respect to each other in a magnetic reproducing apparatus having a rotating magnetic head. In the period from the contact start point Pa to the contact end point Pb (within one scan) with the tape, an example is shown in which the level fluctuation occurs due to the change per head. .

  Therefore, the timing generation circuit 42 generates timing pulses indicated by B1 to B6 in FIG. 8 at a plurality of locations, for example, 6 locations in the period (within one scan) from the contact start point Pa to the contact end point Pb.

  Then, at the timing of each pulse, the reproduction RF signal x output from the detection characteristic circuit 3 is taken into the memory 12 and the reproduction signal data is input from the memory 12 to the adaptive control unit 9 at each timing.

  Therefore, the adaptive control unit 9 calculates the optimum filter tap coefficient T for each timing, and inputs it to the coefficient memory 10 for storing the tap coefficient.

  A combination of tap coefficients T corresponding to each position of the waveform A per head is sequentially input from the coefficient memory 10 to the digital filter 4 at the timing of the timing pulse generated by the timing generation circuit 14. The equalization characteristic by the filter 4 is determined.

  As a result, an optimum filter tap coefficient for each part of the waveform A per head is given to the digital filter 4, and as a result, equalization characteristics necessary for improving the error rate can be obtained, and the error rate can be improved. .

  At this time, as shown in FIG. 8C, the tap coefficients may be switched in a one-to-one correspondence with each of the above timings. Further, the tap coefficients between these timings may be changed by so-called interpolation. Thus, as shown in FIG. 8D, the tap coefficients may be switched at a time interval finer than each of the above timings, so that a steep change in the filter characteristics is alleviated, and the switching of the filter coefficients is further improved. It can be smooth.

  Here, in the case where it takes a long time from reading of reproduction signal data for calculation of equalization processing and interpolation processing to calculation of the optimum tap coefficient, reproduction data one cycle before is obtained using the periodicity of the reproduction RF signal waveform. May be used at the same timing in the current cycle.

Also, as a technique for reducing the level fluctuation of the envelope waveform of the reproduction RF signal at this time, envelope detection of the envelope waveform of the reproduction RF signal is performed, and the detection level information is input to an AGC circuit (variable gain amplifier) not shown. In addition, a technique for improving the error rate at the time of decoding in the decoding signal processing circuit at the subsequent stage by correcting the level of the reproduction RF signal is also presented.
JP-A-5-143908

  Here, when the quality of the reproduced RF signal is relatively good and stable, the automatic equalizer according to the prior art performs adaptive control of the digital filter that is the equalizer, and the optimum filter tap coefficient in a short time. Can be calculated.

  However, when the quality of the reproduced RF signal is low, the conventional technology cannot calculate the optimum tap coefficient in a short time, or even if it can be calculated, there may be a problem in the reliability of the calculated tap coefficient. There is.

  In addition, with the conventional technique based on envelope detection and level correction of the reproduced RF signal by the AGC circuit, it cannot be said that a sufficient correction effect is obtained depending on the setting of the attack time, recovery time, etc. of the AGC circuit. There may be no improvement.

  The present invention has been made to solve such problems, and by controlling the equalizer in accordance with the state of the reproduced signal, a good convergence state can be obtained in a short time, and the convergence stability can be obtained. Another object of the present invention is to provide a storage medium storing a good automatic equalizer, automatic equalization method and automatic equalization program.

  An object of the present invention is to provide an automatic equalizer that controls an equalization characteristic for a reproduction signal in accordance with an equalization error, provided with time constant filter means for performing a filter process on the equalization error, and the time constant filter. This is achieved by controlling the characteristic parameter of the means in accordance with the level of the reproduction signal.

  At this time, even if the characteristic parameter is calculated based on the level fluctuation of the envelope waveform of the reproduction signal, the above object is achieved, and the characteristic parameter is calculated based on the maximum value and the minimum value of the envelope waveform of the reproduction signal. Even if it does so, the said objective is achieved.

  Further, at this time, the above-mentioned object is achieved even if the characteristic parameter is calculated based on the slope of the envelope waveform level of the reproduction signal. Even if it is calculated based on the time variation, the above-mentioned object is achieved.

  Similarly, at this time, even if the characteristic parameter is controlled based on whether or not the level fluctuation of the envelope waveform of the reproduction signal exceeds a predetermined reference value, the above object is achieved, and the envelope of the reproduction signal is achieved. The above object can also be achieved by controlling the waveform level fluctuation and the time fluctuation of the level fluctuation of the envelope waveform of the reproduction signal based on whether or not a predetermined reference value is exceeded.

  Further, at this time, a memory circuit for holding envelope detection information of the reproduced signal is provided, and the characteristic parameter may be calculated based on the envelope detection information held in the memory circuit. The objective is achieved.

  Next, in the automatic equalization method in which the equalization characteristic for the reproduction signal is controlled according to the equalization error, the above object is a processing step of detecting the level of the reproduction signal by envelope detection of the reproduction signal; The above object can also be achieved by including a processing step of controlling a filter time constant characteristic of time constant filter means for performing a filter process on the equalization error based on the level of the reproduced signal.

  Another object of the present invention is a storage medium storing a program necessary for execution of automatic equalization processing in which the equalization characteristic for a reproduction signal is controlled according to an equalization error, and the processing executed by the program A step of detecting a level of the reproduction signal by envelope detection of the reproduction signal, and a filter time constant of time constant filter means for performing a filtering process on the equalization error based on the level of the reproduction signal The above object can also be achieved by a storage medium equipped with an automatic equalization program including processing steps for controlling characteristics.

  According to the embodiment, the present invention provides, as first technical means, a reproduction signal equalization means, an equalization error detection means for detecting an equalization error from the reproduction signal, and the equalization error detection. Time constant filter means for filtering the equalization error detected from the reproduced signal by the means, and the equalization according to the error information detected and filtered by the error detection means and the time constant filter means An automatic equalizer comprising control means for controlling equalization characteristics of the means, envelope detection means for performing envelope detection of the reproduction signal, and timing generation means for generating a timing signal according to the period of the reproduction signal. Thus, an automatic equalizer in a magnetic reproducing apparatus that controls the characteristics of the time constant filter means based on detection information from the envelope detection means is a first technical means. The one in which the features.

  Next, the second technical means is the automatic equalizer described in the first technical means, wherein the control means is based on detection information from the envelope detection means, and the level variation of the envelope waveform of the reproduction signal Is calculated.

  Further, the third technical means is the automatic equalizer described in the second technical means, wherein the control means is a level fluctuation of an envelope waveform of a reproduction signal calculated based on detection information from the envelope detection means. The maximum and minimum values of the waveform level are calculated as numerical values indicating the above.

  Similarly, the fourth technical means is the automatic equalizer described in the second technical means, wherein the control means calculates the level fluctuation of the envelope waveform of the reproduction signal calculated based on the detection information from the envelope detection means. As a numerical value to be shown, the inclination of the waveform level is calculated.

  Further, a fifth technical means is the automatic equalizer according to the second technical means, wherein the control means is adapted to change the level of the envelope waveform of the reproduction signal based on the detection information from the envelope detection means. In addition to the calculation, the time fluctuation of the level fluctuation is also calculated.

  Further, a sixth technical means is the automatic equalizer according to the second technical means, wherein the control means is adapted to detect the level fluctuation of the envelope waveform of the reproduction signal calculated from the detection information from the envelope detection means. The characteristic parameter of the time constant filter means is controlled based on whether or not a predetermined reference value is exceeded.

  Further, a seventh technical means is the automatic equalizer according to the third technical means, wherein the control means is the level fluctuation of the envelope waveform of the reproduction signal calculated from the detection information from the envelope detection means. The characteristic parameter of the time constant filter means is controlled based on whether or not a predetermined reference value is exceeded based on the time fluctuation of the level fluctuation.

  Further, an eighth technical means includes a memory circuit for holding the envelope detection information in the automatic equalizer described in the second or fifth technical means, and the previous control means is provided in the memory circuit. The characteristic parameter of the time constant filter means is controlled based on the envelope detection information held.

  On the other hand, a ninth technical means is a method for performing equalization processing of a reproduction signal in an automatic equalizer, and includes a step of performing envelope detection from the reproduction signal and a time constant filter based on the detected detection information. And a step of controlling the characteristics.

  A tenth technical means is a program for performing equalization processing of a reproduction signal in a digital reproduction device, the step of performing envelope detection from the reproduction signal, and the detection according to the detected error And a step of controlling the time constant filter characteristics based on the detection information.

  As a result, it is possible to control the equalization characteristic adapted to the reproduction state based on the envelope detection information of the reproduction RF signal.

  According to the present invention, the quality of a reproduction RF signal is evaluated using envelope detection information detected from the reproduction signal, and setting control of a time constant filter that performs filter processing for equalization error is performed based on the information. Therefore, flexible control of the equalizer can be performed, and as a result, good convergence of the equalization characteristic can be obtained.

  Hereinafter, an automatic equalizer, an automatic equalization method, and an automatic equalization program according to the present invention will be described in detail with reference to embodiments shown in the drawings.

  FIG. 1 shows an embodiment in which the present invention is used by being incorporated in a magnetic reproducing apparatus as an example. In the figure, 8 is a time constant filter circuit, 11 is an envelope detection circuit, 15 Represents an automatic equalizer according to this embodiment.

  Also in this automatic equalizer 15, the magnetic head 1, the reproduction amplifier circuit 2, the detection characteristic circuit 3, the digital filter 4 as the equalizing means, the decoding circuit 5, the output terminal 6, and the adder (error detector) 7. The time constant filter circuit 8, the adaptive control unit 9, the coefficient memory 10, the memory 12, the input terminal 13, and the timing generation circuit 14 are the same as the automatic equalization filter according to the prior art described with reference to FIG.

  Here, first, the time constant filter circuit 8 performs a filtering process on the equalization error ε detected by the adder 7 so that the filtered error ε ′ is supplied to the adaptive control unit 9. However, at this time, the time constant filter circuit 8 uses the control information c supplied from the adaptive control unit 9 as a characteristic parameter, and thereby the filter time constant is controlled.

  Next, the envelope detection circuit 11 performs envelope detection of the output x of the detection characteristic circuit 3 generated from the reproduced RF signal and supplies the detection output e to the memory circuit 12. Therefore, both the output information x of the detection characteristic circuit 3 and the envelope detection information e from the envelope detection circuit 11 are output from the memory 12 and supplied to the adaptive control unit 9.

  Therefore, the adaptive control unit 9 calculates the tap coefficient T of the digital filter 4 based on both information of the output information (x and e) of the memory 12 and the output information ε ′ of the time constant filter circuit 8, and performs control. The signal c is calculated and the filter time constant of the time constant filter circuit 8 is changed.

  As a result, each component circuit is controlled in a direction in which the equalization error ε converges to zero. As a result, the equalization characteristic of the reproduction circuit is a frequency close to the inverse characteristic of the electromagnetic conversion characteristic during magnetic recording / reproduction. It will be set to be a characteristic.

  Next, the operation of the adaptive control unit 9 necessary for the automatic equalization processing of the reproduction signal according to this embodiment will be described with reference to the flowchart of FIG.

  Here, the flowchart of FIG. 2 calculates the maximum value Lmax and the minimum value Lmin of the level of the envelope waveform based on the envelope detection information of the reproduction signal output from the envelope detection circuit 11, and performs the adaptive control operation. However, in the embodiment of the present invention, the numerical information calculated from the envelope detection information is not limited to the maximum value Lmax and the minimum value Lmin.

  When the processing according to the flowchart of FIG. 2 is started, the adaptive control unit 9 first inputs the envelope detection information e from the envelope detection circuit 11 via the memory circuit 12, and the maximum value Lmax and the minimum value Lmin of the envelope waveform level. Is detected (S101).

  Here, FIGS. 5A to 5E show an example of a reproduction RF signal in a period (within one scan) from the contact start point to the end of contact with the tape as an example. For example, as shown in the figure, the control unit 9 detects the maximum value and the minimum value of the signal level within the period from the contact start point of the tape and the magnetic head to the end of contact (within one scan), and the maximum level of the envelope waveform. The value Lmax and the minimum value Lmin may be used.

After obtaining the maximum value Lmax and the minimum value Lmin in this way, the adaptive control unit 9 calculates the level information difference ΔL based on these (S102). Here, according to the following formula:
ΔL = Lmax−Lmin
Calculate as

  In this calculation example of the level information difference ΔL, normalization is not performed at the time of calculation. However, the average value level Lave of the envelope waveform is calculated and normalized by dividing the level information difference ΔL by the average level Lave. The level information difference ΔL ′ may be used.

  Next, the level information difference ΔL is compared with a preset setting value (reference value) (S103). First, when the comparison result is YES, that is, when the level information difference ΔL is less than the set value, it is determined that the fluctuation of the reproduction RF signal is relatively small, and the set value (filter time constant) of the time constant filter circuit 8 is determined. Control is performed by selecting and setting the filter time constant 1 (S104).

  On the other hand, when the comparison result is NO, that is, when the level information difference ΔL is equal to or larger than the set value, it is determined that the fluctuation of the reproduction RF signal is relatively large. At this time, the set value (filter time constant) of the time constant filter circuit 8 Then, the filter time constant 2, which is a numerical value smaller than the filter time constant 1, is selected and set to perform control (S105).

  As described above, in the present invention, the level information difference ΔL is calculated from the level information obtained by envelope detection of the reproduction signal, is compared with a preset reference value, and the time constant is based on the comparison result. The filter time constant of the filter is set to be different so that the convergence accuracy of the equalization characteristic can be improved.

  Here, when equalizing the reproduction signal as in the present invention, when the level fluctuation of the reproduction signal is small, the filter time constant is improved rather than reducing the filter time constant of the time constant filter to improve the response. Priority is given to performing equalization processing with high accuracy by increasing the value, and conversely, when there are many fluctuations in the level of the reproduced signal, the response can be achieved even if there is a slight decrease in equalization accuracy by reducing the filter time constant. Sex may be a priority.

  In other words, in the above embodiment, when the level variation of the reproduction signal is small, the filter time constant of the time constant filter circuit 8 is reduced to improve the equalization accuracy. The constant is reduced so that the equalization characteristic converges quickly.

  Therefore, according to the above embodiment, the equalizer characteristics are automatically controlled in accordance with the state of the reproduced signal, so that the equalization characteristics converge to a stable state in a short time, and are highly accurate and responsive. Good equalization characteristics can be easily obtained.

  Next, another embodiment of the present invention will be described with reference to FIG. Here, this embodiment is characterized in that the time constant of the time constant filter circuit 8 is not switched when the reproduction signal has a relatively large level fluctuation with a long period. In FIG. 3, 16 is an error memory, and other configurations are the same as those of the embodiment shown in FIG.

  Here, the error memory 16 sequentially calculates the level information difference ΔL in one scan calculated based on the maximum value Lmax and the minimum value Lmin of the envelope waveform level, sequentially for each scan period, over a predetermined plurality of scan periods. It works to update and hold the memory.

  Next, the operation of the embodiment shown in FIG. 3 will be described with reference to the flowchart of FIG. 4. First, in FIG. 4, steps S201, S202, S205, S206, and S207 shown in FIG. , S102, S103, S104, and S105.

  Therefore, also in the flowchart of FIG. 4, when the adaptive control unit 9 starts processing, first, envelope detection information e is input from the envelope detection circuit 11 via the memory circuit 12, and the maximum value Lmax of the envelope waveform level is input. Then, the minimum value Lmin is detected (S201), and then the level information difference ΔL is calculated based on the level information (S202).

  Thereafter, unlike the case of FIG. 2, the level time fluctuation information ΔLt representing the fluctuation of the level information difference ΔL is calculated from the level information difference ΔL just calculated (S203). At this time, the adaptive control unit 9 uses the data held in the error memory 16 and compares the level information differences ΔL before and after the predetermined period to calculate the level time variation information ΔLt.

  At this time, as a reference time unit for calculating the level time variation information ΔLt, it is sufficient to set it to a period that is at least twice the period from the contact start point to the end of contact (one scan period). It is also possible to set one frame period of the TV signal or a longer period than that.

  Next, the level time variation information ΔLt is compared with a preset setting value 1 (reference value 1) (S204). When the comparison result is YES, the process proceeds to step 205, and when the result is NO, the process proceeds to step 208.

  First, when the comparison result is YES, that is, when the level time fluctuation information ΔLt is less than the set value 1, the fluctuation of the reproduction RF signal is relatively small over a considerably long period, that is, a period more than twice the one scanning period. Then, the level information difference ΔL at this time is compared with a preset setting value 2 (reference value 2) (S205).

  If the determination result in step S205 is YES, that is, if the level information difference ΔL is less than the preset setting value 2, it is determined that the fluctuation in the reproduction RF signal in the short period is relatively small, and Control is performed by selecting and setting the filter time constant 1 as the set value (filter time constant) of the constant filter circuit 8 (S206).

  When the comparison result in step S205 is NO, that is, when the level information difference ΔL is equal to or larger than the set value, it is determined that the level fluctuation of the reproduction RF signal is relatively large in a short period, and in this case, the time constant filter circuit As the set value (filter time constant) of 8, control is performed by selecting and setting the filter time constant 2, which is a numerical value smaller than the filter time constant 1 (S207).

  On the other hand, when the result in step 204 is NO and the process proceeds to step 208, it is determined that the level fluctuation of the reproduction RF signal is large even when viewed over a long period of time, and the set value of the time constant filter circuit 8 (filter time) The filter time constant 3 is selected and set as a constant), and control is performed.

  As the filter time constant 3 at this time, a numerical value larger than the filter time constant 2 is generally set, but a numerical value different from the filter time constant 2 may be set, or an equivalent numerical value may be used.

That is, as a setting example,
(Example 1) Filter time constant 3> Filter time constant 1> Filter time constant 2
(Example 2) Filter time constant 3 = Filter time constant 1> Filter time constant 2
Etc.

  Therefore, even according to this embodiment, the equalizer characteristics are automatically controlled in accordance with the state of the reproduced signal, so that the equalization characteristics converge to a stable state in a short time, and the response is highly accurate. It is possible to easily obtain good equalization characteristics.

  At this time, according to the embodiment shown in FIG. 3, when the level fluctuation of the reproduction RF signal is large over a long period of time, it is possible to immediately shift from step S204 to equalization processing with the filter time constant 3.

  By the way, in the embodiment described above, the filter time constant is a fixed value, but it is also possible to use a numerical value that varies as appropriate according to the previous set value of the filter time constant or its transition, and the operation flowchart itself It is also possible to control with hysteresis characteristics.

  In addition, regarding the detection of the maximum value Lmax and the minimum value Lmin of the envelope waveform level by the adaptive control unit 9, the maximum value and the minimum value within the period from the contact start point of the tape and the magnetic head to the end of contact (within one scan). However, the present invention is not limited to this, and the one scan period may be divided into a plurality of periods, and the maximum value and the minimum value may be calculated in each of the divided periods. For example, as shown in B1 to B6 in FIG.

  Further, the numerical information calculated from the envelope detection information in the adaptive control unit 9 of the automatic equalizer 15 is not limited to the maximum value Lmax and the minimum value Lmin as in the above embodiment, but other calculation information But it is possible.

  In this case, for example, it is possible to calculate a differential value (inclination information) or the like of the envelope detection information, and control based on the information, or further control in combination with the maximum value Lmax and the minimum value Lmin.

  In the above embodiment, the reproduction signal equalizing means has been described using a digital filter. However, it is also possible to implement using other equalizing means such as an analog filter.

  In the above embodiment, the automatic equalizer 15 is arranged between the detection characteristic circuit 3 and the demodulation circuit 5, but the present invention is not limited to the block arrangement and is not shown. It may be arranged after the reproduction processing circuit in the subsequent stage, or may be arranged in an automatic equalizer so as to have a block configuration used for various processes.

  In the embodiment described above, an adder (error detector) 7 is used as means for calculating the equalization error, and the error ε is obtained by subtracting the output y of the digital filter 4 from the output d of the decoding circuit 5. Although it is extracted, the present invention can be implemented even if the difference value obtained by extracting the difference between the data actually detected from the reproduction signal and the expected value of the data is used as an equalization error.

  By the way, in the case of a digital VTR or the like, data subjected to error correction coding is recorded on the recording medium. Therefore, a magnetic reproducing apparatus for reproducing such data usually includes an error correction decoding circuit corresponding to the error correction encoding.

  Here, the error correction decoding circuit decodes the data output from the data detection circuit and performs error detection and correction. Therefore, the number of errors or the error rate detected from the error correction decoding circuit is: It represents the equalization of the reproduction signal. Therefore, this error number or error rate may be used as it is as an equalization error of the reproduction signal.

  At this time, the equalization error may be obtained from both the difference value between the data actually detected from the reproduction signal and the expected value of the data and the number of errors detected in the error correction decoding circuit. Good.

  As mentioned above, although the automatic equalizer by this invention was demonstrated using embodiment, the automatic equalizer in this invention is not limited to above-described embodiment. Various modifications can be made to the present invention without departing from the scope of the present invention.

  For example, each function and means in the automatic equalizer of the present invention described above may be implemented as a program executed in a microcomputer for adaptive control of equalization processing, and such an equalization program may be The program may be recorded on a computer-readable program recording medium and may be a storage medium equipped with an automatic equalization program. Further, it may be embodied by any mechanism using an equalization method for realizing automatic equalization processing as described above. You may make it do.

  Furthermore, an automatic equalizer as described above is provided, a mechanism for realizing the equalization method as described above is provided, the equalization program is executed by a computer, or the equalization program is recorded. The equalization program may be read from the program recording medium and executed by a computer to perform automatic equalization processing.

It is a block diagram which shows one Embodiment of the automatic equalizer by this invention. It is a flowchart for demonstrating operation | movement of one Embodiment of the automatic equalizer by this invention. It is a block diagram which shows other one Embodiment of the automatic equalizer by this invention. It is a flowchart for demonstrating operation | movement of other one Embodiment of the automatic equalizer by this invention. It is explanatory drawing of the reproduction envelope waveform which this invention makes object. It is a reproduction | regeneration envelope waveform diagram for demonstrating an example of an adaptive control timing. It is a block diagram which shows an example of the automatic equalizer by a prior art. It is a reproduction | regeneration envelope waveform diagram for demonstrating another example of an adaptive control timing.

Explanation of symbols

1: Magnetic head 2: Reproduction amplifier circuit 3: Detection characteristic circuit 4: Digital filter 5: Decoding circuit 6: Output terminal 7: Adder (error detector)
8: Time constant filter circuit 9: Adaptive control unit 10: Coefficient memory 11: Envelope detection circuit 12: Memory 13: Input terminal 14: Timing generation circuit 15 Automatic equalizer

Claims (10)

In an automatic equalizer that controls the equalization characteristics for the reproduction signal according to the equalization error,
Providing a time constant filter means for filtering the equalization error;
An automatic equalizer characterized in that the characteristic parameter of the time constant filter means is controlled in accordance with the level of the reproduction signal. The automatic equalizer according to claim 1, wherein
The automatic equalizer, wherein the characteristic parameter is calculated based on a level fluctuation of an envelope waveform of the reproduction signal. The automatic equalizer according to claim 1, wherein
The automatic equalizer, wherein the characteristic parameter is calculated based on a maximum value and a minimum value of an envelope waveform of the reproduction signal. The automatic equalizer according to claim 1, wherein
The automatic equalizer, wherein the characteristic parameter is calculated based on a slope of a level of an envelope waveform of the reproduction signal. The automatic equalizer according to claim 1, wherein
The automatic equalizer, wherein the characteristic parameter is calculated based on a level fluctuation of an envelope waveform of the reproduction signal and a time fluctuation of the level fluctuation. The automatic equalizer according to claim 1, wherein
The automatic equalizer according to claim 1, wherein the characteristic parameter is controlled based on whether or not a level fluctuation of an envelope waveform of the reproduction signal exceeds a predetermined reference value. The automatic equalizer according to claim 1, wherein
The characteristic parameter is controlled based on whether or not a level fluctuation of the envelope waveform of the reproduction signal and a time fluctuation of the level fluctuation of the envelope waveform of the reproduction signal exceed a predetermined reference value. Automatic equalizer. The automatic equalizer according to claim 1, wherein
A memory circuit for holding envelope detection information of the reproduction signal is provided;
The automatic equalizer characterized in that the characteristic parameter is calculated based on the envelope detection information held in the memory circuit. In an automatic equalization method in which the equalization characteristic for the reproduction signal is controlled according to the equalization error,
A processing step of detecting the level of the reproduction signal by envelope detection of the reproduction signal;
And a processing step of controlling a filter time constant characteristic of time constant filter means for performing a filter process on the equalization error based on the level of the reproduced signal. A storage medium storing a program necessary for execution of an automatic equalization process in which an equalization characteristic for a reproduction signal is controlled according to an equalization error,
Processing steps executed by the program include:
A processing step for detecting the level of the reproduced signal by envelope detection of the reproduced signal, and a filter time constant characteristic of time constant filter means for performing a filtering process on the equalization error based on the level of the reproduced signal A storage medium storing an automatic equalization program characterized by comprising:

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