JPH08297926A - Data playback device - Google Patents

Abstract

(57) [Summary] [Object] The present invention enables a data reproducing apparatus to improve the detection accuracy of a multilevel detection function even when the amplitude of a reproduced signal suddenly changes. [Structure] The maximum value sampled by detecting and sampling the rectified output obtained by rectifying a multi-valued signal at fixed intervals is used as the envelope signal, and the fixed value must be the maximum value during this detection. By setting the period slightly longer than the minimum period determined by the modulation method and the waveform equalization method so that it can be detected, an accurate envelope signal with high tracking capability for amplitude fluctuations is created. . By adaptively controlling the threshold value used in the signal detection circuit based on the envelope signal, it is possible to improve the detection accuracy of the multilevel detection function even when the amplitude of the reproduction signal suddenly changes.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIGS. 6 to 11) Problem to be Solved by the Invention (FIG. 12) Means for Solving the Problem (FIGS. 1 and 2) Action (FIGS. 1 and 2) Embodiment (1) Configuration of Embodiment (1-1) Overall Configuration of DAT (FIG. 1) (1-2) Configuration of Envelope Creating Circuit (FIGS. 2 to 4) (2) Operation of Embodiment (FIG. 5) (3) ) Effects of Examples (4) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing device,
For example, Digital Audio Tape Recorder (hereinafter D
AT).

[0003]

2. Description of the Related Art Conventionally, in DAT, an integral equalization method has been adopted as an equalization method for reproduction signals. As shown in FIG. 6, the eye pattern of the reproduction signal waveform-equalized by the integral equalization method has a binary waveform. Recording codes to which this type of equalization method is applied (for example, scrambled NRZ (non return to
zero) sign) is superior in signal-to-noise ratio (SN ratio),
It is characterized by being easily affected by low-frequency cutoff.

For this reason, recently, it has been considered to use a block code or NRZI (non return to zero invert) as a recording code of DAT, which has a low frequency component and is hardly affected by low frequency cutoff. Further, as an equalization circuit for these codes, a method using a partial response method which positively utilizes intersymbol interference is being studied. If the reproduced signal equalized by this partial response method is subjected to analog digital conversion based on the channel clock, and the resulting reproduced signal data is subjected to, for example, Viterbi decoding, the audio data will be compared with the integral detection method. Can be detected with few errors.

The eye pattern of the reproduced signal after waveform equalization by this partial response method has a waveform of three values or more. FIG. 7 shows a type of this method, which is a partial response class 1 (hereinafter referred to as PR (1,1)).
3 shows an eye pattern of a signal equalized by. PR
In the case of (1, 1), the voltage at the detection point has three values (here, ± 1 [V] and 0 [V]).

The signal equalized to PR (1,1) is shown in FIG.
It is obtained by the equalization circuit 1 shown in FIG. That is, the equalizer circuit 1 delays the integrated equalized signal S1 shown in FIG. 9 (A) by one detection interval (one cycle of the channel clock) T by the delay circuit 2 to obtain the delayed signal S2 shown in FIG. 9 (C). To generate. Subsequently, the equalization circuit 1 adds the delay signal S2 to the original integrated equalization signal S1 by the adder 3 to generate an equalization signal S3 having a waveform of PR (1,1).

However, since it is easy to explain that the input and output amplitudes are equalized for convenience, as shown in FIG. 8B, the PR equalized signal S3 of the equalization circuit 1 is multiplied by 0.5 to obtain the waveform shown in FIG. 9D. The equalization circuit 4 that outputs the equalized signal S4 shown in is used. The feature of the equalized signal S4 is that one of the integrated equalized signals S1 is
A signal that reaches from peak to peak at the detection interval (hereinafter, 1T
Signal) is canceled out and becomes 0 [V], and the long-period signal that reaches the peak from the peak in two detection intervals or more becomes +1.
[V] or -1 [V].

Incidentally, in the notation of PR (1,1), the data train recorded on the magnetic tape is an isolated pulse "... 00100 ...
... ", the data sequence after waveform equalization is" ... 00110
"..." In addition to this, the PR (1, -1) (that is, the recorded data string is an isolated pulse "... 00100 ...")
, The data sequence after waveform equalization is "... 001-10 ...
, Etc.) or NPR (1, 0, -1) (that is, the recorded data sequence is an isolated pulse "... 00100").
…… ”, the data string after waveform equalization is“ …… 0010
0 …… ”, the data string after waveform equalization is“ …… 001
0-1 ... ”and the like). FIG.
The detection points of the waveform shown in (A) are indicated by arrows.

By the way, when the audio data is detected from the integrated equalized reproduction signal, one threshold value (for example, 0
[V]) and the reproduced signal after equalization are compared and binarized.
For example, the reproduction signal S integrated and equalized to the waveform shown in FIG.
When 1 is binarized, the maximum value of the reproduction signal S1 is always detected for each detection point indicated by the arrows lined up at regular intervals in FIG. In the integral equalization method, before detecting the maximum value,
An automatic gain control circuit (hereinafter referred to as AGC (au
If it is controlled to be constant by a (tomatic gain control) circuit), the maximum value for each detection point will always be a constant value (for example, ± 1 volt) even if amplitude fluctuations occur in the reproduced signal, and audio data can be detected stably. The gain of the AGC circuit can be controlled on the basis of the envelope signal of the reproduction signal that has been integrated and equalized.

In order to create this envelope signal, first, the reproduced signal is double-wave rectified to obtain a rectified signal S5 shown by the solid line waveform in FIG. 9B, and the peak hold circuit 6 shown in FIG. give. In the peak hold circuit 6, the time constant is determined by the capacitor C and the resistor R, and the discharge time constant shapes the rectified signal S5 into the envelope signal S6 shown by the broken line waveform in FIG. 9B. Incidentally, the voltage V across the capacitor C is the initial voltage and the time V ₀ , respectively.
And t, then V = V ₀ exp (−t / CR). The characteristic curve of this voltage V is shown in FIG.

Further, in the integral equalization method, as shown in FIG. 12A, when dropout occurs in the reproduction signal and the amplitude sharply decreases, the discharge time constant is selected to be short. By doing so, as shown by the broken line in FIG. 12B, in the integral equalization method, it is possible to easily obtain an envelope signal that follows an amplitude fluctuation due to signal loss due to head clogging, so-called dropout. As a result, the peak hold circuit having a relatively small discharge time constant is sufficient to generate the envelope signal S6.

On the other hand, when waveform equalization of a signal is performed by the partial response method, only the maximum value is not always detected at the detection point. That is, in the partial response method, the eye pattern of the equalized reproduced signal has a multilevel waveform, and the threshold value used for detection also has a multilevel value.
Therefore, in the partial response method, it is necessary to compare a plurality of threshold values with the reproduced signal after equalization to specify the code value (so-called multi-value detection). For example, as shown in FIG. 7, the threshold value when equalized to PR (1,1) is ± 0.5.
It becomes two of [V].

If there is amplitude fluctuation during this detection, erroneous detection is likely to occur. Therefore, in the DAT that employs the partial response method as the equalization method, the AGC circuit is an essential circuit in order to control the amplitude of the reproduction signal to be substantially constant.
The gain of this AGC circuit can be controlled based on the envelope signal of the reproduction signal after equalization. To create this envelope signal, first rectify the equalized signal S4 and
The rectified signal S7 having the waveform shown by the solid line in (E) is obtained. Then, the rectified signal S7 is applied to the peak hold circuit 6 to obtain the envelope signal S8 shown by the broken line in FIG. 9 (E).

Equalized signal S4 of the partial response system
In such a multilevel signal, the appearance rate of the maximum amplitude (for example, ± 1 [V] in the case of PR (1,1)) is smaller than that in the case of the integral equalization method. Therefore, in the partial response method, when generating the envelope signal, the discharge time constant of the peak hold circuit 6 must be made larger than that in the integral equalization method. As a result, the peak hold circuit 6 can continue to hold the maximum value of the rectified signal S7 that appears only occasionally.

[0015]

However, when the discharge time constant of the peak hold circuit 6 is increased, the followability to abrupt amplitude fluctuation is deteriorated as shown by the envelope signal S9 shown by the broken line waveform in FIG. 12 (E). . Therefore, in the partial response method, if the peak hold circuit 6 having a large discharge time constant is used, the envelope signal at the time of dropout is not correctly created. Therefore, if the peak hold circuit 6 having a large discharge time constant is used, the AGC circuit malfunctions and the audio data at the time of dropout cannot be detected correctly.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a data reproducing apparatus which can improve the detection accuracy of the multilevel detection function even when the amplitude of the reproduced signal suddenly changes.

[0017]

In order to solve such a problem, in the present invention, a waveform equalization circuit waveform-equalizes a reproduction signal reproduced from a recording medium into a multilevel signal and outputs the multilevel signal.
The envelope creating circuit detects the maximum value of the rectified output obtained by rectifying the multilevel signal at regular intervals, and holds the detected maximum value as a sample to create an envelope signal. The signal detection circuit multivalues the code value of the multilevel signal based on a plurality of threshold values obtained by dividing the envelope signal, and decodes the original digital signal.

Further, in the present invention, the waveform equalizing circuit is
The reproduced signal reproduced from the recording medium is waveform-equalized into a multilevel signal and output. The envelope creating circuit detects the maximum value of the rectified output obtained by rectifying the multilevel signal at regular intervals, and holds the detected maximum value as a sample to create an envelope signal. The signal detection circuit multilevel-discriminates the code value of the multilevel signal whose amplitude is controlled to be constant based on the envelope signal based on a predetermined threshold value, and decodes the original digital signal.

[0019]

The maximum value sampled by detecting and sampling the rectified output obtained by rectifying the multi-valued signal at every constant period is used as the envelope signal, and the maximum value must be guaranteed during this constant period. By setting the period slightly longer than the minimum period determined by the modulation method and the waveform equalization method so that it can be detected, an accurate envelope signal with high tracking capability for amplitude fluctuations is created. . By adaptively controlling the threshold value used in the signal detection circuit based on the envelope signal, it is possible to improve the detection accuracy of the multilevel detection function even when the amplitude of the reproduction signal suddenly changes.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Structure of the Embodiment (1-1) Overall Structure of DAT In FIG. 1, reference numeral 7 represents a reproduction system of DAT as a whole,
When performing multi-valued detection, instead of the method of suppressing the amplitude fluctuation of the reproduced signal by the AGC circuit, the threshold value used in the detection circuit is adaptively changed according to the amplitude fluctuation of the reproduced signal. That is, the reproducing system 7 alternately reads the recording tracks formed on the magnetic tape (not shown) by the reproducing heads 8A and 8B.
The reproducing system 7 amplifies the resulting reproduced signals S10 and S11 by the head amplifiers 9A and 9B, respectively, and supplies them to the switch 10 as reproduced signals S12 and S13, respectively.

The switch 10 has reproduced signals S12 and S1.
3 are switched by a head switching pulse S14 to be combined into one signal train, which is output to the equalization circuit 4 as a reproduction signal S15. The equalization circuit 4 publicizes the reproduction signal S15.
Waveform equalization to (1,1) and the resulting equalized signal S16
Is output to the envelope creating circuit 11. The envelope creating circuit 11 creates a waveform in which the maximum amplitude points are connected in sequence for each constant period based on the voltage value of each sampling point of the signal obtained by rectifying the equalized signal S16, and the envelope signal S
It is output to the detection circuit 12 as 17. Further, the envelope creating circuit 11 outputs the delayed equalized signal S18 obtained by delaying the equalized signal S16 so as to be equal to the delay time when creating the envelope signal S17, to the detection circuit 12.

The detection circuit 12 is an envelope creation circuit 1
Two threshold values are created by inputting the envelope signal S17 given from 1 into a threshold value generation circuit (not shown) and dividing the voltage into 1/2 and -1/2. Further, the detection circuit 12 digitizes the delayed equalized signal S18 based on this threshold value,
The audio data S19 is detected by applying Viterbi decoding to the digitalized delay equalized signal S18 and detecting each bit value. The detected audio data S19 is output to the 10-8 conversion circuit 13.

The 10-8 conversion circuit 13 is 8-10 during recording.
The converted audio data S19 is restored and the audio data S20 obtained as a result is output to the error correction circuit 14. The error correction circuit 14 uses the audio data S20.
Error correction was applied to the audio data S obtained as a result.
21 is output to a digital analog conversion circuit (indicated by D / A in the figure) 15.

The digital-analog conversion circuit 15 converts the audio data S21 into an analog signal, and outputs the resulting audio signal S22 to the audio amplifier 16. The audio amplifier 16 uses this audio signal S2
2 is amplified by a predetermined amplification degree, and the audio signal S23 obtained as a result is output to the speaker 17. In this way D
The AT7 reproduces the audio signal digitally recorded on the magnetic tape by using the partial response Viterbi decoding detection method. Incidentally, an equalization circuit (not shown) and a PLL circuit (not shown) which compose the clock reproduction block.
Reproduces the channel clock from the reproduction signal S15 and supplies it to each circuit as a reference clock.

(1-2) Configuration of Envelope Generating Circuit As shown in FIG. 2, the envelope generating circuit 11 supplies the equalized signal S16 output from the equalizing circuit 4 to the rectifying circuit 18 and the equalized signal S16. The peak detection circuit 19 is caused to output a rectified signal S24 obtained by rectifying. Peak detection circuit 19
Detects the peak voltage of the rectified signal S24 for each peak detection period and passes the detected peak voltage S25 to the sample hold circuit 20.

The sample-hold circuit 20 samples the peak voltage S25 when the sample-hold control signal S26 is at "1" level and outputs the sample-hold control signal S26.
Is at "0" level, the peak voltage S25 is held and output as an envelope signal S17. The envelope generation circuit 11 oscillates the oscillator 21 to send the edge detection circuit 22 a rectangular wave signal S27 having a frequency defining the peak detection period of the peak detection circuit 19.

The edge detection circuit 22 uses a rectangular wave signal S27.
An edge pulse is generated by the rising edge of and the edge pulse is output to the sample hold control terminal of the sample hold circuit 20 as a sample hold control signal S26. Further, the edge detection circuit 22 sends the sample hold control signal S26 to the delay circuit 23 and outputs the time d.
Then, the reset signal is applied to the reset terminal of the peak detection circuit 19 as a reset signal S28.

As a result, the peak detection circuit 19 is reset by the reset signal S28 of logic "1" level immediately after passing the detected peak voltage S25 to the sample hold circuit 20 (here after the time d), and Peak detection during the peak detection period can be started. The envelope creating circuit 11 applies the equalized signal S16 to the delay circuit 24 to delay it according to the delay due to peak detection, and outputs a delayed equalized signal S18 that is timed with the envelope signal S17. Incidentally, the oscillation cycle of the rectangular wave signal S27 is the peak detection period + d.

Here, if the integral equalization waveform shown in FIG. 3A is waveform equalized into PR (1,1) by the equalization circuit 4, FIG.
The waveform shown in (D) is obtained as the waveform of the equalized signal S16. The waveform shown in FIG. 3 (D) is rectified by the rectifier circuit 18 to form the rectified waveform shown in FIG. 3 (E), and the peak of this rectified waveform is shown in FIG. 3 (G) at a constant pulse interval of the reset signal S28. When detected for each, the waveform shown in FIG. 3 (F) is obtained. When the peak detection circuit 19 connects the peak levels of the waveform of FIG. 3 (F) immediately before the peak detection operation in the next peak detection period, the envelope signal S17 having an envelope waveform as shown by the solid line of FIG. 3 (H). Is obtained.

The waveform shown by the solid line in FIG. 3H is shown in FIG.
The waveform is a correct envelope waveform as compared with the waveform shown by the broken line in (E). However, the waveform shown by the solid line in FIG. 3 (H) has a problem in the part marked with *. That is, the waveform shown by the solid line in FIG. 3 (H) does not become the waveform shown by the broken line at the portions marked with *, but falls into the waveform shown by the solid line. This is because the 1T signal was continuous during the period corresponding to the part marked with * in the integral equalization waveform shown in FIG.
As a result of equalization to (1, 1), 0 [V] continues, and the peak detection circuit 19 causes ± 1 within the pulse interval shown in FIG.
The reason is that the signal of [V] was not encountered.

For this reason, if the pulse interval (peak detection period) shown in FIG. 3 (G) is lengthened, the problem shown at the mark * will not occur. However, if the peak detection period is made too long, the followability of the envelope signal S17 with respect to the dropout is impaired. For this reason, it is necessary to set the peak detection period to be slightly longer than the maximum possible continuous number of 0 [V].

That is, if peak detection period> (maximum continuous number of 0 [V] +1) × detection interval, the integral equalization waveform shown in FIG. 3 (A) falls within the pulse interval shown in FIG. 3 (G). ±
The peak of 1 [V] will arrive at least once. As a result, it is possible to prevent the problem found in the part marked with *, and to obtain the envelope creating circuit 11 that keeps trackability as much as possible even for dropout. By the way,
The waveform shown in FIG. 3B is a waveform obtained by rectifying the waveform shown in FIG. 3A, and the waveform shown in FIG. 3C is a waveform obtained by delaying the waveform shown in FIG. 3A by one detection interval. is there.

Next, how to set the peak detection period when PR (1,1) is equalized will be considered. In the case of DAT, it is the 8-10 conversion table that defines the maximum number of consecutive 1T signals. However, the conventional 8-
Since there is a code in which 1T signals are infinitely continuous in 10 tables, if equalized to PR (1,1), it becomes 0 infinitely.
There was a possibility that [V] would continue.

In order to solve this, the 8-10 conversion table has been improved so that the maximum number of continuous 1T signals is 13
A -10 conversion table is considered. This new 8-
When the 10 conversion table is used, a maximum of 13 1T signals are continuously repeated like the integral equalization signal shown in FIG. Therefore, as shown in FIG.
0 [V] of the equalized signal S16 when equalized to (1, 1)
The maximum continuous number of is 14 detection intervals. As a result, a peak detection period of at least 15 detection intervals is required to detect ± 1 [V] which is either before or after the equalized signal S16 as a peak.

Here, the peak detection period is set to, for example, 16 detection intervals. In this case, since the DAT channel clock is 9.4 [MHz], the time per clock is 106 [ns]. Therefore, the peak detection period is 106
[NS] × 16 = 1.7 [μS].

(2) Operation of the embodiment In the above configuration, it is assumed that the audio data recorded on the magnetic tape is recorded by using the new 8-10 conversion table.
Consider a case where the reproduction signal S15 having the waveform shown in FIG. Further, the waveform shown in FIG. 5A is assumed to periodically include a pattern (* -marked portion) in which 13 1T signals repeat continuously.

In this case, when the reproduction signal S15 having the waveform shown in FIG. 5A is equalized to PR (1,1),
As shown in (C), the waveform of the equalized signal S16 is 0
[V] periodically includes a waveform that is continuous for 14 periods of the channel clock. The equalized signal S16 shown in FIG.
Is rectified, the rectified signal S having the waveform shown in FIG.
24 is obtained, and this rectified signal S24 also periodically includes a waveform in which 0 [V] is continuous for 14 periods of the channel clock.

The rectified signal S2 having the waveform shown in FIG.
When 4 is peak-held, the peak voltage S25 having the waveform shown in FIG. 5 (E) is obtained. At this time, the peak detection circuit 19 is reset by the reset signal S28 shown in FIG. 5 (F) at a detection interval of 16 cycles of the channel clock, so that the peaks in each cycle are detected.

As a result, the peak detection circuit 19 operates as shown in FIG.
Even if the amplitude of the reproduction signal S15 shown in (A) is reduced due to dropout, 0 of the waveform of the rectified signal S24 is obtained.
It is possible to reliably detect the peak either before or after the waveform in which [V] is continuous for 14 cycles of the channel clock. Further, the peak detection circuit 19 detects the peak in 16 cycles of the channel clock, thereby discarding the amplitude information in the previous section and detecting the current peak value even when the amplitude sharply decreases due to dropout or the like. Therefore, it has high followability.

The sample-hold circuit 20 connects the waveform of the peak voltage S25 shown in FIG. 5 (E) immediately before resetting, and outputs an accurate envelope signal S17 having a waveform as shown by the solid line in FIG. 5 (G). Will be output. As a result, the sample and hold circuit 20 causes the reproduction signal S1
Even if the amplitude of 5 sharply decreases, the accurate envelope signal S17 corresponding to the amplitude of the current section can be given to the detection circuit 12.

Therefore, the detection circuit 12 outputs the reproduction signal S15.
The envelope signal S17 becomes 1 /
By dividing the voltage into 2 and -1/2 to obtain two accurate threshold values corresponding to the amplitude of the current section, the audio data S19 can be detected with much higher accuracy. As a result, accurate audio data S19 can be detected by sufficiently following a sudden change in the amplitude of the reproduction signal S15 that the conventional AGC circuit cannot follow.

By the way, a low-pass filter or an interpolating means based on another principle is inserted at the output end of the envelope generating circuit 11 so that the envelope signal S17 has a smooth waveform as shown by a broken line in FIG. 5 (G). Good.

(3) Effects of the Embodiments According to the above configuration, the peak level for each constant peak detection period of the rectified signal S24 obtained by rectifying the equalized signal S16 is used as the envelope signal S17, and A new 8-10 conversion table and PR so that the maximum value can always be detected at the time of peak detection during a fixed peak detection period.
By setting the 16-channel clock period, which is a slightly longer period than the 15-channel clock period, which is the minimum period determined by the waveform equalization by (1, 1), to follow the amplitude fluctuation It is possible to improve the detection accuracy of the multi-level detection function even when the amplitude of the reproduction signal S15 suddenly changes by creating the envelope signal S17 with high accuracy.

(4) Other Embodiments In the above embodiment, the envelope signal from the equalized signal S16 obtained by waveform-equalizing the reproduced signal S15 recorded by the new 8-10 conversion table into PR (1,1). S17
However, the present invention is not limited to this, and the reproduced signal recorded by any modulation method such as another conversion table is multivalued by any equalization method such as another partial response method. It can also be applied to the case of creating an envelope signal from an equalized signal obtained by waveform equalizing the signal. Also in this case, the fixed peak detection period is set to a period slightly longer than the minimum period determined according to the modulation method and the equalization method so that the maximum value can always be detected during the peak detection. By doing so, a stable envelope signal that does not depend on the pattern of the recording signal can be created, and the same effect as described above can be obtained.

Further, in the above-mentioned embodiment, the case where the threshold value of the detection circuit is adaptively changed according to the amplitude fluctuation of the reproduction signal at the time of multi-valued detection has been described, but the present invention is not limited to this, and the envelope is not limited to this. It can also be applied to a case where the signal S17 is given to the AGC circuit to control the amplitude of the delayed equalized signal S18 to be constant and multi-value detection is performed.

Further, in the above-mentioned embodiments, the case where the present invention is applied to DAT has been described, but the present invention is not limited to this, and can be applied to a reproducing apparatus for video data, an apparatus for reproducing computer data and the like. .

[0048]

As described above, according to the present invention, the maximum value of the rectified output obtained by rectifying a multi-valued signal which is detected and sampled at every constant period is used as the envelope signal, and this constant value is fixed. By setting the period to a period slightly longer than the minimum period determined according to the method of modulation and the method of waveform equalization so that the maximum value can always be detected during this detection, the amplitude fluctuation An accurate envelope signal with high followability is created. By adaptively controlling the threshold value used in the signal detection circuit based on this envelope signal, it is possible to realize a data reproduction device that can improve the detection accuracy of the multi-value detection function even when the amplitude of the reproduction signal suddenly changes. .

Further, according to the present invention, the maximum value of the rectified output obtained by rectifying the multi-valued signal which is detected and sampled at every constant period is set as the envelope signal, and this constant period is detected by this detection. In order to detect the maximum value at all times, by setting the period slightly longer than the minimum period determined according to the modulation method and waveform equalization method, the followability to amplitude fluctuations is high and the accuracy is high. A simple envelope signal is created. By controlling the amplitude of the multilevel signal to be constant based on this envelope signal, it is possible to realize a data reproducing apparatus that can improve the detection accuracy of the multilevel detection function even when the amplitude of the reproduced signal changes suddenly.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a DAT reproducing system according to an embodiment of a data reproducing apparatus of the present invention.

FIG. 2 is a connection diagram showing a configuration of an envelope creating circuit.

FIG. 3 is a waveform diagram showing waveforms of a signal input to and output from an envelope creating circuit and a signal being processed when a peak detection period is not properly set.

FIG. 4 is a waveform diagram showing a waveform of an equalized signal of a reproduced signal recorded by a new 8-10 conversion table.

FIG. 5 is a waveform diagram showing waveforms of a signal input to and output from an envelope creating circuit and a signal being processed when the peak detection period is appropriately set.

FIG. 6 is a pattern diagram showing an eye pattern of a reproduction signal waveform-equalized by an integral equalization method.

FIG. 7 is a pattern diagram showing an eye pattern of a reproduction signal waveform-equalized to PR (1,1).

FIG. 8 is a configuration diagram showing a configuration of an equalization circuit that performs waveform equalization on PR (1,1).

FIG. 9 is a waveform diagram showing various waveforms when a reproduced signal is processed using the AGC circuit.

FIG. 10 is a connection diagram showing a configuration of a peak hold circuit.

FIG. 11 is a characteristic diagram showing the charging characteristics of the voltage across the capacitor of the peak hold circuit.

FIG. 12 is a waveform diagram showing various processed waveforms when the amplitude of the reproduced signal varies.

[Explanation of symbols]

1, 4 ... Equalization circuit, 2 ... Delay circuit, 3 ... Adder,
6 ... Peak hold circuit, 7 ... DAT playback system, 8
A, 8B ... Reproduction head, 9A, 9B ... Head amplifier, 10 ... Switch, 11 ... Envelope creating circuit, 12 ... Detection circuit, 13 ... 10-8 conversion circuit, 1
4 ... Error correction circuit, 15 ... Digital analog conversion circuit, 16 ... Audio amplifier, 17 ... Speaker.

Claims (4)

[Claims] 1. A waveform equalization circuit for waveform-equalizing a reproduced signal reproduced from a recording medium into a multilevel signal and outputting the same, and detecting a maximum value of a rectified output obtained by rectifying the multilevel signal at regular intervals. An envelope creating circuit that creates an envelope signal by holding the detected maximum value as a sample, and based on a plurality of threshold values obtained by dividing the envelope signal, multi-value identifies the code value of the multi-valued signal, And a signal detection circuit for decoding an original digital signal. 2. The certain period is slightly shorter than the minimum period determined according to the reproduction signal modulation method and the waveform equalization method so that the maximum value can be detected without fail during the detection. The data reproducing apparatus according to claim 1, wherein the data reproducing apparatus is set for a long period. 3. A waveform equalization circuit for waveform-equalizing a reproduced signal reproduced from a recording medium into a multilevel signal and outputting the same, and detecting a maximum value of a rectified output obtained by rectifying the multilevel signal at regular intervals. An envelope creating circuit that creates an envelope signal by holding the detected maximum value as a sample, and a multi-value identification based on a predetermined threshold for the code value of the multi-valued signal whose amplitude is controlled to be constant based on the envelope signal. And a signal detection circuit for decoding the original digital signal. 4. The fixed period is shorter than the minimum period determined according to the reproduction signal modulation method and the waveform equalization method so that the maximum value can be detected without fail during the detection. The data reproducing apparatus according to claim 3, wherein the data reproducing apparatus is set for a long period.