JPS6353609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital recording signal reproducing device.

In recording and reproducing digital signals, a differential detection method is generally used as a means for recovering the original digital signal waveform from the signal reproduced from the head. The differential detection method detects the peak of the reproduced waveform by differentiating the head reproduction signal and detecting the zero crossing of this differential signal.The principle is explained in detail below based on the block diagram shown in Figure 1. do. However, in this example, the modulation method is Modified Mirror (hereinafter referred to as
We will discuss the case where ^M2 ) is used.

In Figure 1, 1 is a magnetic tape, 2 is a playback head, 3 is a head amplifier, 4 is an equalizer, 5 is a low frequency generator, 6 is a differentiator, 7 is a zero cross detector, 8 is a voltage comparator, and 9 is a reference. Voltage input terminal, 1
0 is an ungate circuit, 11 is a flip-flop circuit, and 12 is an output terminal.

In the above configuration, the reproduced signal a shown in FIG. 2C output from the head amplifier 3 has a change in amplitude and peak position due to waveform interference. Therefore, this waveform interference is removed by equalizing the waveform with the equalizer 4, and by the differential action of the equalizer 4, the equalizer 4 shown in FIG.
The high-frequency noise component that is emphasized relatively to the output b of is removed in advance by the next low-frequency filter 5. When the signal b whose waveform has been equalized by the equalizer 4 is differentiated by the next differentiator 6, an output signal c having a waveform shown in FIG. . When the zero cross detector 7 detects the zero cross of this signal c,
As shown in FIG. F, _a pulse signal d is output which includes pseudo _zero -cross pulses such as d ₇ .

On the other hand, the voltage comparator 8 compares the voltage of the waveform-equalized signal b that has passed through the low-frequency converter 5 at a certain threshold level 13 (shown by the chain line in FIG. By obtaining a gate signal e as shown in FIG. G corresponding to the peak position of The pseudo zero cross pulse d ₇ included in the pulse signal d is removed by the processing.
By operating the flip-flop circuit 11 with the zero-crossing pulse f extracted in this way as shown in FIG. 12H, the original recorded waveform g as shown in FIG. In FIG. 2, A indicates a data string l, and B indicates an ^M2 modulation waveform m corresponding to the data string l.

Incidentally, in order to record a large amount of information with a limited amount of tape consumption, such as in a digital video tape recorder, the recording density must be increased. In order to increase the recording density, it is necessary to lower the relative speed of recording or to narrow the track width, but this results in a significant deterioration of the signal-to-noise ratio. Moreover, when the recording density is increased,
Bit interference due to peak shifts and the like becomes a major problem. Therefore, in order to reduce this bit interference as much as possible, waveform equalization becomes necessary.
The SN ratio deteriorates. In other words, if waveform equalization is insufficient, errors will tend to occur due to waveform interference, concentrating on a specific recorded waveform pattern, and conversely, if waveform equalization is insufficient, the SN ratio will rapidly deteriorate and random errors will occur. Errors will increase.

Therefore, in a system where the SN ratio is not very good, it is necessary to perform appropriate waveform equalization in consideration of errors caused by waveform interference and errors caused by deterioration of the SN ratio.

However, when performing appropriate waveform equalization in consideration of the SN ratio and waveform interference, the following disadvantages occur. The situation is shown in FIGS. 3A to 3H based on the differential detection method of the first configuration. In FIG. 3, signals indicated by b' to g' are similar to the signal waveforms b to g explained in FIG. First, for the reproduced signal a from the head amplifier 3, as shown in FIG.
If incomplete waveform equalization as shown in b' is performed, the output signal c' of the differentiator 6 and the output signal d' of the zero-cross detector 7 in this case are D' in the same figure, respectively.
And the waveform is shown in E, and in this case also the signal
During d', there are zero cross pulses d' ₇ in addition to d' ₁ to d' ₆ corresponding to the regular peak positions of the waveform-equalized signal b'.
A pseudo zero-crossing pulse as shown in ... will occur. Therefore, these pseudo zero-cross pulses d′ ₇ . . . must be removed by a gate pulse. However, if the waveform equalization is not sufficient, the peak of the equalized waveform for a particular pattern (for example, three isolated consecutive inversion patterns) in signal b' will be significantly smaller than other peaks, as shown in Figure 3. There exists a case in C as shown by b′ ₀ . Even when the peak becomes extremely small in this way, the gate pulse must be generated correctly, so the threshold level set in the voltage comparator 8 must necessarily be as shown at 13' in Figure 3C. I have no choice but to lower it. However, lowering the threshold level ultimately reduces the margin for noise. For example, if the waveform-equalized signal b' shown by the solid line in FIG. That is, the waveform of the gate signal e' similarly changes from the waveform shown by a solid line to that shown by a broken line, as shown in FIG.

If the zero-crossing pulse d' is gated by the gate signal e' having the waveform shown by the solid line, the output signal f' of the AND gate circuit 10 will be as shown by the solid line in G in the same figure, and only the correct zero-crossing pulse can be extracted. However, if the gate signal e' is as shown by the broken line, a pseudo zero-cross pulse f' ₀ as shown by the broken line in G in the figure will also be taken out at the same time. Therefore, the restored waveform g' created by these zero-crossing pulses f' becomes as shown in H in the same figure, and a pseudo-inversion as shown in _g'0 in the figure occurs, causing an error at this point. Become.

As explained above, if the SN ratio is not sufficient,
Accurate signal reproduction is not possible with conventional differential detection methods.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a digitally recorded signal reproducing apparatus that is capable of accurately reproducing signals based on a differential detection method even in a system with a poor signal-to-noise ratio.

An embodiment of this invention is shown in FIG. That is, this digital recording signal reproducing apparatus has the configuration of the conventional example shown in FIG.
A second equalizer 1 is connected to the input side of the head amplifier 3 and further performs waveform equalization processing on the output b whose waveform has been equalized by the equalizer 4 which is directly connected to the output side of the head amplifier 3.
4 is provided to suppress the degree of waveform equalization of the signal input to the differentiator 6 side to prevent deterioration of the SN ratio, and to increase the degree of waveform equalization of the signal input to the voltage comparator 8 side. The threshold level in the voltage comparator 8 can be set high.

The operation of this digital recording signal reproducing device is explained in the fifth section.
The following description will be made based on the waveform diagram shown in the figure.

The signal b' of the equalized waveform shown in FIG. 5D obtained by moderate waveform equalization by the first equalizer 4 is
Before being input to the voltage comparator 8, the signal is further passed through the second equalizer 14, and is subjected to almost complete equalization processing as shown by b in FIG. By doing this, although the SN ratio deteriorates, the threshold level can be set at the position with the largest noise margin (1/2 of the peak value), as shown at 13'' in Figure 5E. As shown in Figure H, the gate signal e' can be generated at the correct position.On the other hand, the signal entering the differentiator 6 remains moderately equalized in waveform, and the necessary SN ratio is sufficiently secured. Ru.

In the following, due to the same operation as in the conventional example, the gate signal e'' as shown in H in the same figure is affected by the fluctuation (indicated by the broken line) due to noise in the signal b of the equalized waveform shown in E in the same figure. Even if this gate signal
The variation in e'' is minute as shown by the broken line, and can be set as the correct gate signal e''. In other words, when the zero-crossing pulse d'' shown in G in the same figure is gated with the gate signal e'', a correct zero-crossing pulse f'' from which the pseudo zero-crossing pulse d'' ₇ ... is removed is obtained as shown in I in the same figure, and this zero-cross The flip-flop circuit 11 is triggered by the pulse f'', and a correct recorded waveform g'' as shown in FIG. 2J is reproduced.

As described above, the digital recording signal reproducing device of the present invention includes a first equalizer that equalizes the waveform of a reproduced signal from the digital signal recording device to such an extent that a predetermined SN ratio is maintained, and an output of the equalizer. a differentiator for differentiating, a zero cross detector for detecting the zero cross of the output of this differentiator as a pulse signal, a second equalizer for re-equalizing the waveform of the output of the equalizer, and a second equalizer for receiving the output of the second equalizer. A voltage comparator that outputs a gate signal synchronized with the peak value, an AND gate circuit that outputs the logical product of the detection signal of the zero-cross detector and the gate signal, and the digital data restored by receiving the output of the AND gate circuit. Because it is equipped with a flip-flop circuit that
When applied to a recording/reproducing system in which it is difficult to secure a signal-to-noise ratio, it is possible to avoid errors caused by waveform interference and errors caused by deterioration of the signal-to-noise ratio, and to perform accurate signal reproduction.

[Brief explanation of drawings]

Fig. 1 is a block configuration diagram showing a conventional example, Fig. 2 is a waveform diagram showing its operating principle, Fig. 3 is an operating waveform diagram showing its problems, and Fig. 4 is a block diagram showing an embodiment of the present invention. The configuration diagram and FIG. 5 are its operating waveform diagrams. 1...magnetic tape, 2...playback head, 3...
Head amplifier, 4... Equalizer (first), 5...
...Low frequency converter, 6...Differentiator, 7...Zero cross detector, 8...Voltage comparator, 10...AND gate circuit, 11...Flip-flop circuit, 13''
...Threshold level, 14...Equalizer (second).

Claims (1)

[Claims] 1. A first equalizer that equalizes the waveform of a reproduced signal from a digital signal recording device to the extent that a predetermined SN ratio is maintained, a differentiator that differentiates the output of the equalizer, and a zero cross of the output of this differentiator. a zero-cross detector for detecting a pulse signal; a second equalizer for re-equalizing the waveform of the output of the equalizer; and a voltage comparator for receiving the output of the second equalizer and outputting a gate signal synchronized with its peak value. , an AND gate circuit that outputs a logical product of the detection signal of the zero-cross detector and the gate signal, and a flip-flop circuit that receives the output of the AND gate circuit and restores digital data.