JPH09185871A - Digital signal reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute optimum equalization processing to a reproduction signal from each recording medium by controlling a group delay characteristic depending on a kind of the recording medium. SOLUTION: An input video signal is compressed by DCT and quantization or the like in a recording signal processing circuit 1 and the result is fed to a modulation circuit 2. The circuit 2 applies digital modulation processing to the compressed digital video signal to convert the signal into a signal with a form suitable for recording and the converted signal is fed to an amplifier 3. An output of the amplifier 3 is fed to a head 5 via a switch 4 and recorded on a tape 6. In the case of reproduction, original digital data are detected and converted into 1/0 signal and fed to a reproduction signal processing circuit 10. The circuit 10 applies nearly inverse processing to that at recording to obtain the original digital video signal. An equalization circuit 8 of the reproduction system is provided with an amplitude correction section, a group delay correction section and a tape discrimination device and selects a group delay characteristic of plural all pass filters being components of the group delay correction section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal reproducing device, and more particularly to a device for reproducing digital signals from recording media of different types.

[0002]

2. Description of the Related Art Conventionally, as this type of device, a digital VTR for compressing the information amount of a digital video signal and recording it on a magnetic tape is known.

In such a digital VTR, since a large amount of information is recorded, high density recording is required, and both the head and the tape are designed for high density recording.

Up to now, in the digital VTR, a medium having magnetic anisotropy in the in-plane direction such as a metal-coated tape (hereinafter referred to as MP tape) has been often used. But M
With P tape, there is a limit to increasing the recording density due to the demagnetization effect during recording.

On the other hand, metal evaporated tape (hereinafter referred to as M
An obliquely vapor-deposited medium such as E tape) has a magnetic anisotropy of a certain angle in the vertical direction and thus has little recording demagnetization effect and is excellent in high-density recording. However, the MP tape is superior in terms of reliability and cost.

As described above, each of the two types of tape has its own advantages and disadvantages, and it is considered to use the tapes properly according to the purpose of use.

[0007]

In addition to the features described above, MP and ME tapes also have the feature that the response waveform at the time of recording and reproduction differs due to the difference in magnetic anisotropy.
An example of the reproduced waveform of each tape is shown in FIG.

As is clear from FIG. 12, the MP has a front-back symmetrical single-peak waveform, and the ME has a dipulse waveform with a rearward undershoot.

In the digital VTR as described above,
The reproduced data is detected by performing waveform equalization processing on the reproduced signal. The equalization characteristics in this equalization process are designed based on the reproduced waveform.

Since the reproduction waveforms of MP and ME have largely different characteristics as described above, an equalization circuit having a single equalization characteristic can properly equalize the reproduction signals from both tapes. It will be impossible.

Therefore, in the conventional digital VTR, the kind of tape that can be used is naturally determined, and as described above, the tape cannot be used properly according to the purpose of use, and lacks flexibility.

An object of the present invention is to solve the above problems.

Another object of the present invention is to obtain optimum equalization characteristics with a simple circuit configuration.

[0014]

SUMMARY OF THE INVENTION In order to solve the conventional problems and achieve the above object, the present invention is an apparatus for reproducing digital signals from a plurality of types of recording media having mutually different reproduction waveform characteristics. A reproducing means for reproducing a signal from the recording medium; an equalizing means having at least a first-order all-pass filter for equalizing the signal reproduced by the reproducing means; and the reproducing means for reproducing the signal. And a control means for controlling the group delay characteristic of the equalization means according to the output of the discrimination means.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a digital VT which is an embodiment of the present invention.
It is a block diagram which shows the principal part structure of R.

In FIG. 1, the input digital video signal is compressed in the recording signal processing circuit 1 using a technique such as DCT or quantization, and is output to the modulation circuit 2. The modulation circuit 2 performs digital modulation processing on the compressed digital video signal to convert it into a signal of a format suitable for recording, and outputs the signal to the amplifier 3. The amplifier 3 amplifies the modulated video signal and outputs it to the head 5 via the switch 4. The head 5 records the video signal supplied via the switch 4 on the tape 6.

Next, at the time of reproduction, from the tape 6 to the head 5
The video signal reproduced by is amplified by the amplifier 7 and output to the equalization circuit 8. The equalizing circuit 8 compensates for the difference in the reproduced waveform as described above depending on the type of tape as described later, and also compensates the amplitude and group delay characteristic of the reproduced signal in the electromagnetic conversion system and outputs the compensated signal to the demodulation circuit 9. The demodulation circuit 9 demodulates the equalized reproduction signal, detects the original digital data, converts the original digital data into 1 and 0 signals, and outputs the signals to the reproduction signal processing circuit 11. The reproduction signal processing circuit 10 subjects the reproduction signal to processing which is almost the reverse of that at the time of recording to convert it into the original digital video signal and outputs it.

The operation of the equalizing circuit 8 having such a structure will be described below.

FIG. 2 is a diagram showing the configuration of the equalization circuit 8.

The first equalization circuit 8 is composed of an amplitude correction unit 101, a group delay correction unit 102 and a tape discriminator 104,
The group delay characteristics of a plurality of all-pass filters forming the group delay correction unit 102 are switched according to the type of tape.

In this embodiment, the tape discriminator 104
Identifies the type of tape by detecting the resistance value of a metal terminal (not shown) provided in the cassette c.

Now, the relative speed between the head and the tape is 1
When the recording wavelength is 0.2 m / s and the recording wavelength is 0.49 μm, M
The response waveforms of the E tape and MP tape are as shown in FIG.

Waveform analysis is performed on this waveform, and the optimum amplitude characteristic and group delay characteristic of the equalization circuit for each waveform response are obtained as shown in FIG. As is apparent from FIG. 3, the tapes have similar target characteristics with respect to the amplitude characteristics, but have different group delay characteristics with respect to the group delay characteristics, particularly in the low frequency range.

FIG. 4 shows the configuration of the amplitude correction unit 101 and the configuration of the group delay correction unit 102 in this embodiment for realizing these characteristics. As shown in the figure, in this embodiment, as the group delay correction circuit, one active type first-order all-pass filter and three second-order all-pass filters having the group delay characteristics as shown in FIG. 6 are used. .

The group delay characteristic of the first-order all-pass filter is t1 (f) = 2Q / (f × f + Q × Q) The group delay characteristic of the second-order all-pass filter is t (f) = (f ² −fa / Q × f + fa ² ) / (f ² +
It can be expressed as fa / Q × f + fa ² ), and by varying Q and fa (resonance frequency), the magnitude of the group delay and the peak frequency can be adjusted to realize a desired group delay characteristic.

For example, in the first-order all-pass filter shown in FIG. 5, Q = CR / 2π, and in the second-order all-pass filter, fa = (1 / LC) × (1 / 2π) and C (C0- Fa can be changed by controlling C2) and L (L0 to L2). Further, Q = (fa / 2π) CR, and Q can be changed by changing the variable resistance R (R0 to R2).

In this embodiment, the group delay characteristics are changed by fixing the values of fa of the three all-pass filters and variably controlling Q.

Now, let Q of the first-order all-pass filter be Q
0, and Q1 and fa of the second-order all-pass filter are Q1, f1, Q2, and f2, respectively, and f1 = 11 MH
When z and f2 = 19 MHz are set, Q0 = 0.9, Q1 = 1.0, Q2 = 0.7 for the MP tape and Q0 = 2.3, Q1 = 1.
The target characteristic shown in FIG. 3 can be realized with 1, Q2 = 1.0.

In this embodiment, the modulation circuit 2 is used for recording.
Has been subjected to interleaved NRZI processing. Therefore, during reproduction, the equalization circuit 8 performs integral equalization processing, and the demodulation circuit 10 performs the reverse processing, that is, reverse I-NRZI processing, on the reproduction signal. Such a process is a technique which has been particularly used in recent years as a recording / reproducing technique using a partial response (PR (1,0, -1) in this embodiment), and recording is performed by giving intersymbol interference during recording. However, by removing this intersymbol interference during reproduction, it is possible to suppress the influence of intersymbol interference that accompanies high-density recording.

As described above, in this embodiment, C and L are adjusted according to the fa of each of the two second-order all-pass filters.
Is set, and the group delay characteristic of the equalization circuit is switched by switching the values of R of the three all-pass filters according to the discrimination result of the tape discriminator 104 and changing the Q of the three all-pass filters. You can

Therefore, one equalizer circuit is used for MP, ME
Optimal equalization characteristics can be realized for both. Moreover, at this time, in this embodiment, since the group delay correction unit is composed of the all-pass filter, it is possible to obtain the optimum equalization characteristic for each tape with a simple structure. Therefore, the data can be accurately detected from the reproduction signal.

In the above-described embodiment, the group delay characteristics of all three all-pass filters are switched, but as described above, there is a difference in the target characteristics of the group delay correction circuit between the MP tape and the ME tape in the low range. Since it is large, a part of a plurality of all-pass filters, particularly Q0 of the first-order all-pass filter that corrects the low-frequency group delay characteristic, is switched to change only the low-frequency group delay characteristic. Good.

That is, as shown in FIGS. 7 and 8, according to the output of the tape discriminator, Q is switched by switching R0 of the first-order all-pass filter that corrects the group delay characteristic in the low frequency band. Change the group delay characteristics in the low frequency range.

With such a configuration, as shown in FIGS.
Compared with the configuration shown in (1), the number of switching points is one, and the adjustment is easy.

Next, another configuration example of the equalization circuit 8 shown in FIG. 1 will be described.

In FIG. 9, a transversal filter and a first-order all-pass filter are used as the equalizing circuit 8. Then, as in the above-described embodiment, the tape discriminator 104
The type of tape to be used is discriminated by the microcomputer 107
The characteristics of these filters are controlled by.

The structure of the transversal filter 105 is shown in FIG. In FIG. 10, the transversal filter 105 is an IIR filter with one tap and three taps.
The FIR filter is used to integrate the reproduced waveform with the IIR filter, and the FIR filter enhances the high frequency range and corrects the group delay characteristic.

As described above, the difference between the group delay characteristics in the low band of the MP tape and the ME tape is large, and when the difference between the target characteristics and the equalization circuit characteristics in the group delay characteristics of the low band is large, an error occurs in the reproduced data. Many occur. In order to correct all group delay characteristics with the IIR filter, it is necessary to increase the number of taps and to perform complicated calculation of tap coefficients.

Therefore, in this embodiment, the MP tape and ME
The difference in the low-frequency group delay characteristic from the tape is compensated by switching R0 of the first-order all-pass filter shown in FIG.

By using the first-order all-pass filter, optimum characteristics can be realized as compared with the case where both the amplitude and the group delay are corrected only by the transversal filter. Further, it is not necessary to increase the number of taps of the transversal filter or calculate tap coefficients.

In the above embodiment, the ME tape and the M tape are used.
The case where the present invention is applied to a digital VTR using a P tape has been described, but the present invention is not limited to this, and reproduction equalization is performed on recording media having different reproduction waveforms, particularly recording media having different group delay characteristics. If so, the present invention can be applied and has the same effect.

In the above embodiment, the amplitude correction unit 10
Although the group delay correction unit 102 is provided in the subsequent stage of 1, the equalizers may be provided in reverse.

In the above embodiment, the digital signal is detected from the equalized signal by using Viterbi decoding. However, the present invention is not limited to this, and a conventionally used integral detection method may be used.

[0045]

According to the present invention, since the group delay characteristic is controlled according to the type of recording medium, a group of reproduced signals from a recording medium having different reproduced waveforms, particularly those having different group delay characteristics. The difference in delay characteristics can be compensated, and the optimum equalization processing can be performed on the reproduced signal from each recording medium.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital VTR as an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of the equalization circuit of FIG.

FIG. 3 is a diagram for explaining the operation of the circuit of FIG.

FIG. 4 is a diagram showing a configuration of an amplitude correction unit in FIG.

5 is a diagram showing a configuration of a group delay correction unit in FIG.

6 is a diagram showing a group delay characteristic of the all-pass filter in FIG.

7 is a diagram showing another configuration of the equalization circuit in FIG.

8 is a diagram showing a configuration of a group delay correction unit in FIG.

9 is a diagram showing still another configuration of the equalization circuit in FIG.

10 is a diagram showing a configuration of a transversal filter in FIG.

11 is a diagram showing a configuration of a first-order all-pass filter in FIG.

FIG. 12 is a diagram showing reproduced waveforms of an ME tape and an MP tape.

[Explanation of symbols]

 8 Equalization circuit 10 Demodulation circuit 101 Amplitude correction unit 102 Group delay correction unit 104 Tape discriminator

Claims (12)

[Claims] 1. An apparatus for reproducing a digital signal from a plurality of types of recording media having mutually different reproduction waveform characteristics, comprising reproduction means for reproducing a signal from the recording medium, and at least a first-order all-pass filter, Equalization means for performing equalization processing on the signal reproduced by the reproduction means, discrimination means for discriminating the type of the recording medium on which the reproduction means reproduces the signal, and the equalization means for discriminating the output of the discrimination means. A digital signal reproducing apparatus comprising: a control unit that controls a group delay characteristic of the conversion unit. 2. The digital signal reproducing apparatus according to claim 1, wherein the control means switches the group delay characteristic of the first-order all-pass filter according to the output of the discrimination means. 3. The digital signal reproducing apparatus according to claim 1, wherein the equalizing means further includes a plurality of second-order all-pass filters. 4. The control means switches all group delay characteristics of the first-order all-pass filter and the plurality of second-order all-pass filters according to the output of the determination means. Digital signal playback device. 5. The control means is responsive to the output of the discriminating means for the primary all-pass filter and the plurality of filters.
The digital signal reproducing apparatus according to claim 3, wherein the group delay characteristics of some of the following all-pass filters are switched. 6. The equalization means further includes a transversal filter, and the control means switches the group delay characteristic of the first-order all-pass filter in accordance with the output of the discrimination means. 1. The digital signal reproducing device according to 1. 7. The digital signal reproducing apparatus according to claim 6, wherein the control unit switches a group delay characteristic by switching a Quality Factor of the first-order all-pass filter. 8. The equalizing means has an amplitude correction circuit for correcting the amplitude characteristic of the signal reproduced by the reproducing means, and a group delay characteristic correcting circuit for correcting the group delay characteristic of the output of the adding means. The digital signal reproducing device according to claim 1, wherein 9. The digital signal reproducing apparatus according to claim 8, wherein the group delay correction circuit includes the first-order all-pass filter and the second-order all-pass filter. 10. The digital signal reproducing apparatus according to claim 1, wherein the recording medium includes a metal coating type tape and a metal vapor deposition type tape. 11. The discriminating means includes means for detecting a resistance value of a terminal provided in a cassette containing the tape, and the type of the tape is detected based on the resistance value. Item 12. The digital signal reproducing device according to item 11. 12. A head for tracing a tape to obtain a digital signal, a primary all-pass filter for filtering the digital signal obtained by the head, and a secondary for filtering the digital signal obtained by the head. All-pass filter, discriminating means for discriminating the type of tape, and control means for changing the quality factor of at least a part of the primary all-pass filter and the secondary all-pass filter according to the output of the discriminating means. And a digital signal reproducing device including.