JPH0772976B2 - Magnetic signal recording / reproducing apparatus for digital signals - Google Patents

Description

The present invention relates to a magnetic recording / reproducing apparatus for a digital signal such as a digital VTR, and more particularly to a system suitable for its reproducing equalizing circuit.

[Conventional technology]

Conventionally, in a magnetic recording / reproducing apparatus for digital signals, especially in the case of NRZ recording, "Technical Report of the Institute of Electronics and Communication Engineers MR78-13
(August 25, 1978) ”, it is pointed out that the equalization method called integral detection is one of the effective methods. However, it does not mention the problem in realizing the integration method.

[Problems to be solved by the invention]

The above-mentioned conventional technique has a problem of compensation of the group delay time characteristic occurring in the signal band, particularly when the integrating circuit is formed of passive elements. An object of the present invention is to provide an effective compensation method for the group delay time generated in the signal band.

[Means for solving problems]

It has been found that the above-mentioned object is not necessarily required to compensate the group delay time over the entire signal band when the integrating circuit is provided by an equivalent circuit as shown in FIG. That is, as a result of examining the lower limit frequency in the experiment, it was found that the lower limit frequency can be achieved by compensating the group delay time in the frequency region of ωT _D = 1 or more. However, ω = 2π ,: frequency, T _D = R ₂ C
Is. The present invention provides a highly reliable recording / reproducing apparatus for digital signals by providing the minimum group delay time compensating circuit as described above.

[Action]

FIG. 3 shows a digital signal magnetic recording / reproducing apparatus.
The frequency S of the reproduction response of the signal and the equalization characteristic are shown separately for the component I by the integrating circuit and the high-frequency compensation component H.

In the magnetic recording / reproducing system, the magnetic head generates an output voltage proportional to the change of the magnetic flux generated on the magnetic tape, and thus exhibits a so-called differential characteristic proportional to the frequency in the low frequency region.
In the high frequency range, the loss due to the length of the magnetic head gear tape and the loss due to the spacing between the magnetic head and tape become dominant, and the response decays with frequency. However, it is known that the group delay time characteristics are flat due to the electromagnetic conversion action of the magnetic head and the tape. On the other hand, the equalizing circuit has the role of flattening the frequency characteristic of such a magnetic recording / reproducing system. Integral characteristics on the low frequency side and high frequency compensation are required.
As can be seen from FIG. 3, the frequency of ω T _D = 1 is the frequency at which the integration characteristics almost end, and the frequency at which high frequency compensation almost starts. In other words, the frequency close to the frequency at which the recording / reproducing system has a peak response. is there.

For high frequency compensation, for example, when a circuit called a cosine equalizer using a delay line is used, the group delay time becomes constant.
However, the integrating circuit is represented by an equivalent circuit as shown in FIG. The group delay time characteristic at this time is calculated as follows.

The phase characteristic θ (ω) in the integrating circuit of FIG. 2 is Is. However Is. In order for the integral characteristic to continue for more than one digit in the frequency domain, β must be about 15 or more.

The group delay time characteristic D (ω) is And from equation (1) Becomes

From equation (3), In the range of, D (ω) = T _D (1-β) <0, which is a negative value and is a substantially constant group delay. On the contrary In consideration of β 〉〉 1, a positive value, Therefore, it has a complicated characteristic that the sign is reversed on the low frequency side and the high frequency side. However, on the other hand, as described above, since the group delay time characteristic is flat in the magnetic exchange action of the magnetic head and the tape, when the group delay time changes in the signal band in the integrating circuit, the signal waveform is distorted and the code error is reduced. It may occur.

As described above, the group delay time characteristic of the integrating circuit is complicated, and compensating the group delay time characteristic of the entire band becomes complicated in terms of the circuit configuration, and the integrating circuit represented by the equivalent circuit of FIG. 2 is not practical. Was said.

Considering the magnetic recording / reproducing characteristics, the digital signal to be recorded / reproduced desirably has a frequency distribution of the digital signal substantially equal to the reproduction response of the magnetic recording / reproduction system shown in FIG. 3, and a modulation code close to the distribution is used. It is usually used. That is, there are few components of the digital signal to be reproduced that are close to direct current. Therefore, considering this property of the digital signal, it has been found that it is not necessary to flatten the group delay time characteristic of the entire band, and it is sufficient to flatten the frequency above a certain frequency.

FIG. 4 shows the result of measuring the error rate of the reproduced digital signal when the lower limit frequency for compensating the group delay time of the integrating circuit is changed.

As can be seen from the figure, when ωT _D = 1 or less, there is almost no change in the error rate, and it is found that the compensation is unnecessary.

Based on the above experimental results, the present invention realizes a digital signal recording / reproducing apparatus with few code errors while minimizing the circuit scale by compensating the group delay time characteristic at a frequency of ωT _D = 1 or more of the integrating circuit. be able to.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The reproduction signal of the magnetic head 1 is amplified by the preamplifier 2, the integration characteristic is given by the integration circuit 3, and then the high frequency band is compensated by the cosine equalizer 4. The group delay time generated in the integrating circuit 3 is compensated by the group delay time compensating circuit 4.

NRZ at 52 m / s head tape relative speed and 92 Mb / s record transfer speed
The integration circuit constants for recording / reproducing a digital signal and the circuit constants of the group delay time compensation circuit are shown in the figure.

FIG. 5 shows group delay time characteristics in the entire system. ω T _D =
Up to the lower limit frequency of 1 is within ± 5nsec, 92Mb /
The detection window width of s is within 11 nsec.

The cosine equalizer 4 is composed of a delay line 4-1, an attenuator 4-2 and a differential amplifier 4-3. Since the delay line is used, the group delay time is constant and the high frequency band can be compensated.

In the group delay time compensating circuit 5, the output of the cosine equalizer 4 is configured as a two-output amplifier 5-1 to form an inverted output and a normal output,
The two emitter followers 5-2 and 5-3 mix the two signals via the capacitance C _P 5-4 and the resistor R _P 5-5 to change the phase and compensate the group delay time. . Reference numeral 5-6 is an output amplifier.

〔The invention's effect〕

According to the present invention, the code error due to the adjustment error of the group delay time of the equalization circuit of the digital signal recording / reproducing circuit can be substantially reduced to zero while the circuit scale is minimized, which is effective as an equalization method. A simple integration method can be put to practical use. As a result, high reliability of the digital VTR can be obtained.

[Brief description of drawings]

FIG. 1 is a signal system diagram of a reproduction equalization circuit according to an embodiment of the present invention,
FIG. 2 is a diagram showing a configuration of an integrating circuit, FIG. 3 is a diagram showing typical characteristics of a reproducing response frequency characteristic of a magnetic recording / reproducing system, an integrating circuit frequency characteristic, and a high frequency compensation frequency characteristic. The figure shows the result of measuring the error rate by changing the compensation range of the group delay time, and FIG. 5 is an example of the residual group delay time characteristic. 3 ... Integrator circuit, 5 ... Group delay time compensation circuit.

Claims (3)

[Claims] 1. A head (1) for detecting a digital signal recorded on a magnetic recording medium, an integrating circuit (3) for integrating and outputting the detected digital signal, an output signal of the integrating circuit, and the like. And a delay time compensating circuit (5) for compensating for the group delay time of the output of the compensating circuit. The delay time compensating circuit is provided when the digital signal is reproduced. A magnetic recording / reproducing apparatus for digital signals, which is characterized by compensating for a group delay time in a frequency region only higher than a peak frequency of a reproduction response. 2. The magnetic recording / reproducing apparatus according to claim ₁ , wherein the integrating circuit is equivalently represented by a resistor R ₁ , a capacitance C, and a resistor R _2. . 3. A frequency region in which the residual time due to the difference between the group delay time characteristic of the integrating circuit and the group delay time characteristic of the delay time compensating circuit is smaller than the detection window time of the digital signal, f = 1 / (2π ) × T _D (where T _D = CR ₂ ), the magnetic recording / reproducing apparatus according to claim 1 or 2, wherein the region is higher than the frequency value given by T _D = CR ₂ .