JPS6243246B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reproducing digitally recorded signals, and in particular, by integrating the reproduction signal of a magnetically recorded NRZ signal, the differential characteristics due to the winding of a magnetic head during reproduction can be determined. The signal obtained by correcting the voltage is passed through a voltage comparator to determine whether it is "1" or "0", and when reproducing the original recorded NRZ signal, the comparison voltage of the voltage comparator is determined from the voltage comparator input waveform.
By extracting the signal using the DC regeneration circuit, the effect of low frequency component noise generated in the reproduction head and the first stage of the regeneration amplifier and emphasized by the integration circuit is reduced.

First, let's start with the conventional NRZ signal regeneration circuit.
It is shown in the figure and an overview of its operation will be explained. The reproduction signal from the reproduction head is amplified by the reproduction amplifier, the equalizer corrects the deterioration of high frequency characteristics caused by various losses in the recording and reproduction system, and the following integration circuit calculates the differentiation due to the winding of the reproduction head. The characteristics are corrected to obtain an NRZ signal waveform that is almost close to the original recording signal waveform. Here, _the thermal noise generated from the resistance of the impedance of the reproduction head and the low frequency component of the noise of the reproduction amplifier are emphasized by the integrating circuit, which has a _negative effect on signal reproduction. Low frequency components below f _L (=1/2πC ₀ R ₀ ) are removed in advance by a blocker and guided to a voltage comparator through a buffer amplifier. A voltage fixed approximately at the center of the buffer amplifier output signal is used as the comparison voltage of the voltage comparator. A "1" or "0" determination is made by this voltage comparator, and further, the timing is readjusted by a D flip-flop based on this signal and the clock signal, and the original recorded NRZ signal is reproduced.

The operation of the conventional NRZ signal regeneration circuit has been described above, but in this case, the low frequency blocker naturally removes the low frequency components of the signal, and f _L
Depending on the selection method, inter-symbol interference may occur, which may have an adverse effect on voltage comparison; however, in order to avoid this adverse effect, the cutoff frequency f _L due to C ₀ and R ₀ must be set to 1/500 or less of the bit frequency. No. For this reason, noise in a frequency range higher than 1/500 of the bit frequency could not be removed, which had the disadvantage of adversely affecting voltage comparison.

Therefore, the present invention aims to remove the influence of the low frequency components in the noise as described above, and includes the comparison reference voltage of the voltage comparator in the comparison input signal in the NRZ signal regeneration circuit. This was done with the focus on the fact that the effects of low-frequency component noise contained in such signals can be removed by tracking slow fluctuations in the signal.

Below, among the NRZ signal regeneration circuits according to the present invention,
In particular, we will discuss the operation of the DC regeneration circuit. From the buffer amplifier output signal in Fig. 2, D ₁ and C ₁ extract the positive peak of the signal during a certain period, that is, the positive quasi-peak, and D ₂ and C ₂ similarly extract the signal during a certain period. Extract the negative peak, that is, the negative quasi-peak. The average value of the positive and negative quasi-peak voltages is taken out at point E using R ₃ and R ₄ (see Figure 3 C, D, and E), and this voltage is divided using VR ₁ , and the voltage comparator Used as a comparison voltage. VR ₁ is set to optimize the comparison voltage according to the magnitude of the positive input voltage of the voltage comparator.

With the above configuration, as shown in Figure 3B, voltage comparison can be performed accurately at the center of the waveform even if the center position of the waveform slowly changes upward or downward due to superimposition of low-frequency noise. Therefore, the influence of low frequency component noise can be reduced.

FIG. 4 shows the effect of the present invention. The figure shows the conventional circuit configuration without DC regeneration.
Due to the effects of C ₀ and R ₀ , the sine wave noise margin becomes large at frequencies below f _L (in this case, 1/500 of the bit frequency). τ _d = τ _i (where τ _d is the discharge time constant of DC regeneration, τ _i is the low-frequency cutoff time constant) in Fig. 4 is for the NRZ signal regeneration circuit according to the present invention, and is approximately 1/100 of the bit frequency. The sine wave noise margin starts to increase from the frequency of .

Next, the optimum value of the discharge time constant τ _d for DC regeneration will be explained below. τ _d =0.1τ _i in Figure 4 is DC
When the regeneration discharge time constant is made small, in this case, when a long continuous waveform of "1" or "0" occurs in the signal, it becomes difficult to extract the positive and negative peaks correctly. Therefore, Fig. 4 τ
As _d = 0.1τ _i , the sinusoidal noise margin becomes poor for high frequencies. Furthermore, if the discharge time constant of DC regeneration is increased to τ _d = 10τ _{i ,} the comparison voltage will no longer follow the fluctuations in the center voltage due to _noise , so the There is little improvement in the frequency sine wave noise margin.

As mentioned above, the discharge time constant of the DC regeneration circuit is
Good results can be obtained when the time constant is approximately matched to the low frequency cutoff.

FIG. 5 shows an example of the noise spectrum of the reproducing system of a digital magnetic recording/reproducing apparatus using the DC reproducing circuit of the present invention. The noise spectrum of the voltage comparator input is extremely large in the portion where the frequency is less than 2×10 ^-2 of the bit frequency, as shown by the solid line in FIG. However, when the NRZ signal reproducing circuit of the present invention was used, the effective noise decreased as shown by the dotted line in the same figure, and no increase in middle and high frequency noise was observed.

By implementing the present invention, magnetically recorded
When determining the reproduction signal of an NRZ signal, the differential characteristics due to the winding of the reproduction head are corrected by an integrating circuit, and when reproducing the same NRZ signal as the recorded signal, the low frequency emphasized by the correction integrating circuit The influence of component noise can be reduced without deteriorating the noise characteristics of high frequency components.

As explained above, the present invention can reduce the effect of emphasized low-frequency noise by correcting the low-frequency characteristics when passing an NRZ signal through a system with large low-frequency attenuation. Therefore, it can be used when transmitting NRZ signals through a transmission line with large attenuation in the low frequency range, such as cable transmission.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional digital recording signal reproducing circuit, FIG. 2 is a block diagram showing an example of the configuration of a digital recording signal reproducing circuit according to the present invention, and FIG. FIG. 4 is a characteristic curve diagram showing an example of the noise frequency vs. bit frequency characteristic, and FIG.
The figure is a characteristic curve diagram showing an example of the equivalent noise spectrum.

Claims (1)

[Scope of Claims] 1. In a digital recording signal reproducing device, a reproduced signal obtained by an integrating circuit having a characteristic opposite to the differential characteristic due to the winding of the reproducing head is passed through a low-pass filter and then filtered according to a predetermined standard. In reproducing the original recorded digital signal by comparing voltages, a peak rectifier circuit having a discharge time constant approximately equal to the time constant of the low-pass filter is obtained by the integrating circuit; A digital recording signal reproducing method characterized in that positive and negative quasi-peaks of the reproduced signal passed therethrough are respectively detected, and a center voltage of these positive and negative quasi-peaks is set as the reference voltage for the voltage comparison. 2. The digital recording signal reproducing method according to claim 1, wherein an NRZ signal or a modified NRZ signal is used as the digital signal.