JP2508492B2 - Magnetic playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial field of use B Outline of the invention C Conventional technology (Fig. 3) D Problems to be solved by the invention (Figs. 4 and 5)
E) Means for solving problems (Figs. 1 and 5) F Action (Fig. 1) G Example (Figs. 1, 2 and 5) H Effect of invention A Industrial BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic reproducing apparatus, and is particularly suitable for being applied to reproducing digital data recorded on a magnetic recording medium.

B. Summary of the Invention According to the present invention, in a magnetic reproducing apparatus for reproducing a digital signal in which a DC signal component is suppressed, an equalizer circuit having an equalizing characteristic for suppressing a frequency range corresponding to the DC signal component is provided. As a result, it is possible to effectively suppress intersymbol interference and further improve the reproduction bit error rate.

C Prior Art As a magnetic reproducing apparatus of this type, the magnetic reproducing apparatus has been conventionally applied when reproducing a PCM audio signal in an 8 mm video tape recorder (8 mm VTR).

That is, in the 8 mm VTR, as a standard recording format, as shown in FIG. 3 (A), a pair of rotating heads (that is, A head and B head) are helically scanned on the magnetic tape 1 as a recording medium. Allows the recording track TR to cross the magnetic tape 1 diagonally.
A and TRB are formed, the FM video signal is recorded in the video track portion TR _VD of each recording track TRA and TRB, and the standard recording pattern is formed by recording the PCM audio signal in the audio track portion TR _AD. It is done like this.

Thus, the audio track portion of the pick-up signal picked up by the A and B heads during reproduction is
PCM demodulation of the PCM audio signal obtained from TR _AD to reproduce the audio signal, and FM demodulation of the FM video signal obtained from the TR _{VD of} the video track section to reproduce the video signal, thus supporting the video signal program. The audio signal can be recorded and reproduced on the magnetic tape 1 at a high density.

By the way, the standard format recording format as shown in FIG. 3A can record the PCM audio signal in the video track TR _VD of the recording patterns of the recording tracks TRA and TRB. The magnetic tape 1 dedicated to audio information can also be recorded and reproduced by using an 8 mm VTR.

That is, as shown in FIG. 3 (B), the recording track TR
A and TRB have 6 audio track parts TR _AD1 , TR _AD2 ...
... divided into TR _AD6, these recording track TR _AD1 ~TR _AD6
By recording the PCM audio signals of the first to sixth channels, it is possible to realize the magnetic tape 1 capable of selectively recording and reproducing the audio signals of 6 channels.

Further, as shown in FIG. 3 (C), the recording track TRA
, TRB with 12 audio track parts TR _AD01 , TR _AD02 ...
… PCM that is divided into TR _AD12 and PCM-modulated at the Nyquist frequency twice as high as the PCM audio signal recorded in TR _AD1 and TR _AD2 … TR _AD6 in Fig. 3 (B)
By recording the audio signal in the audio track portion of each channel, the magnetic tape 1 capable of selectively recording and reproducing the audio signal of 12 channels can be realized.

By the way, when reproducing a digital signal from the magnetic tapes 1 having different recording patterns as shown in FIGS. 3A, 3B and 3C while maintaining compatibility, the reproduction bit error rate is As a method of suppressing the value to a sufficiently low value for practical use, by arranging digital data of logical “H” or “L” level so as not to be continuous, such as 8-10 modulation and 8-9 modulation, A and B are arranged. It has been considered to apply a method (so-called DC-free coding method) for preventing a direct current component from being superimposed on a pickup signal picked up by a head.

D Problem to be Solved by the Invention However, when the digital data is recorded / reproduced on / from the magnetic tape 1 by using this DC-free encoding method, if an equalization process that satisfies the Nyquist criterion is executed, it is practical. There is a problem that the upper crosstalk becomes large.

That is, when recording and reproducing a digital signal on the magnetic tape 1, the data detection signal S taken out by the reproducing circuit
_DT is equivalently obtained by transmitting the digital recording signal S _REC supplied from the input terminal T _IN to the output terminal T _OUT to the electromagnetic conversion system digital transmission line MG as shown in FIG. Therefore, the data detection signal
Play bit error rate of S _DT is significantly affected Te cowpea the transmission characteristics of the electromagnetic conversion system digital transmission line MG.

Here, the electromagnetic conversion system digital transmission line MG is an input terminal
The digital recording signal S _REC supplied to T _IN is sent to the magnetic tape 1 via the digital signal recording circuit 2 and the recording head 3.
The recorded digital signal recorded above is picked up by the reproduction head 4 and output as a data detection signal S _DT via the digital signal detection circuit 5 to the output terminal T _OUT.
Sent to

Considering the electromagnetic conversion system digital transmission line MG having such a configuration, in order to prevent the reproduction bit error rate of the data detection signal S _DT from deteriorating, theoretically, intersymbol interference should be prevented from occurring. As shown in B), the electromagnetic conversion system digital transmission line MG has frequency characteristics that practically satisfy the Nyquist first and second standards.
It is considered that the digital signal detection circuit 5 may be used for equalization.

In the case of FIG. 5 (B), it is assumed that the digital recording signal S _REC is, for example, 8-10 modulated after sampling the recording information at the sampling frequency f _CK (= 14.8 [MHz]).

Therefore, if a frequency characteristic that ideally satisfies the Nyquist first standard can be set, a flat response is obtained at a frequency equal to or lower than the Nyquist frequency f _NY (= 7.4 [MHz]), as shown by an ideal characteristic curve K1. Data detection signal
If S _DT can be obtained, the reproduced digital information can theoretically be picked up without error.

On the other hand, in practice, the response of the spectrum of the data detection signal S _DT exhibits a change that inclines at the Nyquist frequency f _{NY as} shown by the practical characteristic curve K2, but it is ideal according to the second standard of Nyquist. Characteristic curve K1
The area of the deviations D1 and D2 of the practical characteristic curve K2 for
D1 = to be D2, if setting the transmission characteristics of the electromagnetic conversion system digital transmission line MG, is considered possible to obtain a digital error-free data as a data detection signal S _DT.

Under such a theoretical principle, a data detection signal having a frequency response approximating the practical characteristic curve K2 of FIG. 5 (B).
If the equalization characteristics of the digital signal detection circuit 5 are set so as to obtain S _DT , it is theoretically possible to prevent intersymbol interference. Therefore, in practice, the digital information can be obtained with a sufficiently low bit error rate. It is believed that you can play.

Actually, the frequency characteristic of the electromagnetic conversion system from the recording head 3 to the reproducing head 4 via the magnetic tape 1 is as shown by a characteristic curve K11 in FIG. 5 (A).
Due to recording demagnetization phenomenon, spacing loss, loss of gears, etc., it has a maximum value at a frequency of approximately 2 [MHz] and is cut off at 0 [MHz] and 8 [MHz] from the maximum value. It has a frequency response characteristic that produces an increasing curve portion K11A and a decreasing curve portion K11B.

On the other hand, as described above with reference to FIG.
The digital signal obtained by 8-10 modulating the digital data obtained by sampling at the sampling frequency f _CK = 14.8 [MHz] is
As shown by the characteristic curve K12 in FIG. 5 (C), it has no DC component, but has a frequency spectrum extending from the low frequency component to the frequency component of the sampling frequency f _CK , and has a maximum value between them. It exhibits various frequency characteristics.

Thus, the frequency characteristic as shown by the electromagnetic conversion characteristic curve K11 (FIG. 5 (A)) is shown in FIG. 5 (D) by the equalization characteristic curve K13 in the digital signal detection circuit 5 (FIG. 4). If equalization is performed as shown, a data detection signal S _DT having a frequency characteristic such as a practical characteristic curve K2 (FIG. 5 (B)) can be obtained.

The equalization characteristic curve K13 of FIG. 5 (D) shows that the frequency f is f =
When increasing from 0, the frequency f is approximately f = 0 to 2
A decrease curve portion K13A is generated during the frequency range F1 up to [MHz], and the frequency f is approximately f = 2 to 6 [MH] following the minimum value.
During the frequency range F2 of z], the increasing curve portion K13B is generated, and when the frequency f becomes approximately f = 6 [MHz] or more following the maximum value, the decreasing curve portion K13C is generated.

Here, the first decreasing curve portion K13A corresponds to the increasing curve portion K11A of the characteristic curve K11 of the frequency characteristic of the electromagnetic conversion system (FIG. 5 (A)), and is the practical characteristic curve K2 Equalization is performed as in the flat portion K2A in FIG.

Further, the increasing curve portion K13B of the equalization characteristic curve K13 is
Of the 11 decreasing curve portions K11B, the practical characteristic curve K2 (FIG. 5 (B)) corresponds to the range from the flat portion K2A to the frequency at which it starts to fall, and this frequency range is set to the practical characteristic curve K2. Equalize like the flat part K2B.

The second decreasing curve portion K13C of the equalization characteristic curve K13 corresponds to the remaining curve portion of the decreasing curve portion K11B and equalizes it like the decreasing curve portion K2C of the practical characteristic curve K2.

In this way, theoretically the first and second Nyquist
The digital signal detection circuit 5 can be provided with equalization characteristics that satisfy the standard, and thus the data detection signal S
_It is theoretically considered possible to prevent a reproduction error from occurring in the _DT , and the equalization characteristic of the digital signal detection circuit 5 is conventionally set by such a method.

However, in this case, since the digital signal recorded on the magnetic tape 1 uses the 8-10 modulation which is the DC-free coding method, the frequency characteristic curve K12 of the digital recording signal S _REC (see FIG. 5 ( In C)), when the frequency f is f = 0, the response is extremely reduced in practical use (that is, the state in which the DC component is not included), so that there is a problem that crosstalk increases.

Incidentally, although the frequency f of the digital recording signal S _REC is sufficiently small in practical use, the equalization characteristic curve K13 of the digital signal detection circuit 5 greatly emphasizes the signal component in the vicinity of f = 0 by the decreasing curve portion K13A. Since the equalization is performed as described above, other signal components that are not originally the signal components of the digital recording signal S _REC are emphasized as the signal components of the data detection signal S _DT , and as a result, intersymbol interference actually occurs, and eventually the data Detection signal S
_This results in a worse _DT bit error rate.

The present invention has been made in consideration of the above points, and an object thereof is to propose a magnetic reproducing apparatus which can prevent the above-mentioned deterioration of the bit error rate.

E Means for Solving the Problems In the present invention, in order to solve the above problems, the magnetic reproduction in which the digital data recorded on the magnetic recording medium 1 is picked up by the electromagnetic conversion system MG to form a reproduction signal. In the device, by emphasizing the pickup signal component of the increasing curve characteristic portion K11A in the low frequency region of the frequency characteristic of the electromagnetic conversion system MG, a flat equalized frequency characteristic is given to the signal component in the low frequency region of the reproduction signal. The first equalizer means 12 and the equalization frequency that cuts off the signal component in the frequency region near the direct current of the reproduction signal by suppressing the pickup signal component in the frequency region near the direct current in the increase curve characteristic portion K11A. The second equalizer means 13 for giving the characteristic and the decreasing curve characteristic portion K1 in the high frequency region of the frequency characteristic of the electromagnetic conversion system MG. By suppressing the 1B pickup signal component, a third equalizer means 14 for providing an equalized frequency characteristic that cuts off the signal component in the high frequency region of the reproduced signal is provided.

The F-action equalizer circuit 14 equalizes the pick-up signal S1 so that the DC signal component not originally included in the recorded digital signal is not unnecessarily emphasized. _Intersymbol interference in S _DT can be suppressed, and thus the reproduction bit error rate can be further reduced in practical use.

G Embodiment One embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1 in which parts corresponding to those in FIG. 4 are designated by the same reference numerals, the digital signal detection circuit 5 transmits the pick-up signal S1 sent from the reproduction head 4 through a reproduction amplifier circuit 11 to a first equalizer circuit 12 Give to.

The first equalizer circuit 12 has two stages of delay circuits 12A and 12B connected in cascade. The input terminal, the output terminal of the delay circuit 12A and the output terminal of the delay circuit 12B are respectively weighted by the weighting circuits 12C, 12C.
Addition is performed in the addition circuit 12F via D and 12E, and the addition output is input to the second equalizer circuit 13 as the equalizer output S2 of the first equalizer circuit 12.

Thus, the first equalizer circuit 12 raises the frequency component in the high frequency region of the pick-up signal S1 as shown by the characteristic curve K21 in FIG. 2 (A) from the minimum value level to form the emphasis curve portion K21B. By performing the equalization processing in this manner, the pick-up signal S1 is emphasized by the emphasis curve portion K21B in the frequency range corresponding to the decrease curve portion K11B of the frequency characteristic of the electromagnetic conversion system (FIG. 5 (A)).

The second equalizer circuit 13 is connected to the first equalizer circuit 12
The equalizer output S2 is received by the integrating circuit 13A and the differentiating circuit 13B, the integrated output S3 and the differential output S4 are added by the adding circuit 13C, and the result is sent out as the equalizer output S5.

Thus, the second equalizer circuit 13 obtains an integrated output S3 in which the signal component is emphasized by integrating the low frequency component close to the DC component in the equalizer output S2 in the integrating circuit 13A, and the equalizer output S2 in the differentiating circuit 13B. By taking out the pulse component of as the differential output S4 and adding it to the integrated output S3 in the adder circuit 13C,
As shown by the characteristic curve K21 in FIG. 2 (A), the increasing curve portion K11A of the frequency characteristic of the electromagnetic conversion system (FIG. 5 (A)).
In the frequency range corresponding to, the equalizer output S2 is raised from the minimum value level and is emphasized so as to form the emphasized curve portion K21A.

In this way, the frequency characteristic of the electromagnetic conversion system is used as the equalizer output S5 of the second equalizer circuit 13 (FIG. 5 (A)).
When the frequency changes around the frequency corresponding to the maximum value of, the pickup signal S1 is emphasized accordingly, and the pickup signal S1 is electromagnetically converted in the electromagnetic conversion system including the magnetic tape 1 and the reproduction head 4. The equalization processing is performed so that the distortion of the frequency characteristic given at the time of making it approximates the flat frequency characteristic.

The equalizer output S5 of the second equalizer circuit 13 is given to the third equalizer circuit 14. As shown by the characteristic curve K22 in FIG. 2 (B), the third equalizer circuit 14 has a frequency response characteristic having a cut-off frequency at a frequency f ₁₁ close to direct current (for example, f ₁₁ = 300 [Hz]). With. As a result, the equalizer output S6 of the third equalizer circuit 14 is, as shown by the characteristic curve K23 in FIG. 2 (C),
Equalizer output S5 frequency characteristics (Fig. 2 (A)) of the equivalent curve portion K23B corresponding to the emphasis curve portion K21B, while equalizer output S5 equivalent to the low frequency range emphasis curve portion K21A The suppression curve portion K23C that cuts off the signal component in the frequency region close to the DC component (that is, the frequency range of f ₁₁ = 300 [Hz] or less) in the emphasis curve portion K23A is formed.

Thus, a signal having a frequency characteristic that the DC signal component included in the equalizer output S5 and the frequency component in the vicinity thereof are suppressed and is not included in the equalizer output S6 is obtained as the equalizer output S6.

This equalizer output S6 is given to the fourth equalizer circuit 15. The fourth equalizer circuit 15 has a second Nyquist circuit as shown by a characteristic curve K24 in FIG.
In order to obtain a frequency characteristic curve corresponding to the practical characteristic curve K2 (FIG. 5 (B)) representing the standard, the Nyquist frequency f _NY
It has a decreasing curve section K24B whose cutoff frequency is a slightly lower frequency.

As a result, the equalizer output S7 of the fourth equalizer circuit 15
As shown by the characteristic curve K25 in FIG. 2 (E), the suppression curve corresponding to the suppression curve portion K23C, the emphasis curve portions K23A, K23B in the characteristic curve K23 (FIG. 2 (C)) of the equalizer output S6. In addition to the section K25C and the emphasis curve sections K25A and K25B, a suppression curve section K25D that suppresses so as to cut off frequency components higher than the Nyquist frequency f _NY is generated.

In this manner, the equalizer output S7 obtained by equalizing the pick-up signal S1 in the first to fourth equalizer circuits 12 to 15 is the data detection signal in the data detection circuit 16.
It is converted to S _DT and sent to the output terminal T _OUT .

In the case of this embodiment, the data detection circuit 16 compares the equalizer output S7 with the 0 cross reference voltage S11 provided from the reference voltage source 22 in the comparison circuit 21, and thus the comparison output S12 whose logic level changes at the timing of the 0 cross point. Is D
It is given to the D input terminal of the synchronizing circuit 23 of the flip-flop circuit configuration, and the PLL (phase l
ocked loop) is given to the clock generation circuit 25 having a circuit configuration.

Thus, the reproduction clock signal S13 is generated at the output end of the clock generation circuit 25 and is applied to the clock input end of the synchronization circuit 23, whereby the reproduction clock signal S1 is generated.
The logic level of the comparison output S12 at the timing of 3 is sent from the Q output terminal as the data detection signal _SDT .

In the above configuration, the pick-up signal S1 sent from the electromagnetic conversion system is equalized by the digital signal detection circuit 5, so that the data detection signal S _DT having the frequency characteristic as shown in FIG. Is converted to.

That is, the first and second equalizer circuits 12 and 13 allow the frequency components of the electromagnetic conversion system (FIG. 5 (A)) whose response is lowered to be picked up by the emphasis curve portions K25B and K25A. By equalizing the signal S1 by emphasizing it and forming the suppression curve portion K25D by the fourth equalizer circuit 15, the Nyquist first and second criteria described above with reference to FIG. 5B are satisfied. Data detection signal S _DT with frequency characteristics
(FIG. 5 (E)) can be obtained.

In addition to this, the third equalizer circuit 14 suppresses the frequency component having a frequency close to the direct current component by forming the suppression curve portion K25C. As described above, when a digital signal in which the direct current component is sufficiently suppressed is recorded on the magnetic tape 1, the signal component in the low frequency region is detected as the data detection signal S.
_By not including it in the _DT , the intersymbol interference of the data detection signal S _DT can be effectively suppressed by this amount, and as a result, the reproduction bit error when the digital data is reproduced based on the data detection signal S _DT. The rate can be suppressed to a much lower value.

In the above-described embodiment, the digital signal using 8-10 modulation is recorded in order to obtain the DC-free coded signal, but the present invention is not limited to this, and the point is that the DC component is not included. The present invention can be widely applied to the case of recording and reproducing a digital signal coded in the above format through an electromagnetic conversion system.

Further, in the above-described embodiments, the case where the magnetic tape is used as the electromagnetic conversion system has been described, but the recording medium is not limited to this, and various magnetic recording media such as a magnetic disk can be applied.

H Effect of the Invention As described above, according to the present invention, by providing an equalization circuit that suppresses the DC signal component in the pick-up signal sent from the electromagnetic conversion system, intersymbol interference is reduced. Therefore, it is possible to easily realize a magnetic reproducing apparatus capable of reproducing data having a bit error rate that is sufficiently low in practical use.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic reproducing apparatus according to the present invention, FIG. 2 is a characteristic curve diagram for explaining the equalizing operation of the equalizer circuit, and FIG. 3 is a schematic diagram showing a recording pattern of a magnetic tape. A diagram, FIG. 4 is a system diagram showing an equivalent circuit of an electromagnetic conversion system, and FIG. 5 is a characteristic curve diagram showing frequency characteristics of each part thereof. 1 ... Magnetic tape, 4 ... Playback head, 5 ... Digital signal detection circuit, 12, 13, 14, 15 ... First, second, third, fourth equalizer circuit, 16 ... Data detection circuit .

Claims (1)

(57) [Claims] 1. A magnetic reproducing apparatus for picking up digital data recorded on a magnetic recording medium by an electromagnetic conversion system to form a reproduction signal, wherein the frequency characteristic of the electromagnetic conversion system is increased in a low frequency region. A first equalizer means for giving a flat equalized frequency characteristic to the signal component in the low frequency region of the reproduction signal by emphasizing the pick-up signal component of the curved characteristic portion, and a frequency near DC in the increasing curve characteristic portion. Second equalizer means for providing an equalized frequency characteristic that cuts off the signal component in the frequency region close to the direct current of the reproduction signal by suppressing the pickup signal component in the region; and the frequency characteristic of the electromagnetic conversion system. By suppressing the pickup signal component of the decreasing curve characteristic part in the high frequency region, Magnetic reproducing apparatus characterized by comprising a third equalizer means for providing the equalizing frequency characteristics as to cut-off the signal components of the high frequency range.