JPH087936B2 - Digital signal detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal detecting apparatus in a digital data recording / reproducing apparatus.

2. Description of the Related Art As a recording / reproducing apparatus for digital information, various methods have been researched and developed, and some have been put into practical use. These devices record digital data on a recording medium after performing predetermined signal processing, and at the time of reproduction, read a signal recorded on this recording medium into a digital signal wave and then perform predetermined signal processing. This is to restore the original digital data.

By the way, in the digital recording / reproducing apparatus, the modulation method and the detection method play a very important role in terms of the recording density of digital information and the frequency of error occurrence. The modulation method has an interface function for matching the characteristics of digital data to be recorded with the transmission characteristics of a recording / reproducing system that is a transmission path. On the other hand, the detection method has a function of restoring the signal extracted from the recording medium into digital data.

Therefore, when a magnetic tape is used as a recording medium, a conventional example thereof will be shown below.

FIG. 5 is a block diagram showing a conventional example.
In the figure, 47 is a data input terminal, 48 is a modulator, 49 and 51 are magnetic heads, 50 is a magnetic tape, 52 is an equalizer, 53 is an integrator, 54 is a detector, 55 is a demodulator, 56 is a data output terminal. The digitally processed data string is applied to the modulator 48 via the data input terminal 47. The output from the modulator 48 is recorded on the magnetic tape 50 via the magnetic head 49. On the other hand, during reproduction, information recorded on the magnetic tape 50 is read out via the magnetic head 51, various deteriorations are corrected by the equalizer 52, and then integrated by the integrator 53. The output of the integrator 53 is shaped into a binary data string by the detector 54, demodulated by the demodulator 55, and the reproduced data string is sent out via the data output terminal 56.

In FIG. 5, the waveform of each part when the modulation method is NRZ is shown in FIG. In the figure, 57 is a data input terminal 47
The data string that is input via the
Reference numeral 59 is the output waveform of the equalizer 52, waveform 60 is an ideal integrated waveform when there is no distortion in the DC component or low frequency component, and waveform 62 is an integrator when there is distortion in the DC component or low frequency component. The output waveform of 53, the dashed lines 61 and 63 are the threshold values in the detector 54,
Reference numerals 65 to 67 are detection timing errors attributed to deterioration of DC components and low frequency components, and 64 is an output waveform of the detector 54.

Since the NRZ is assumed as the modulator 48, the output waveform of the modulator 48 is the waveform 58. By the way, in a transmission line composed of a magnetic tape, a magnetic head and a rotary transformer (hereinafter referred to as "tape head system"), the gain is lowered due to various losses due to high frequency components, and the differential of the reproducing magnetic head and the rotary transformer is caused. Due to the characteristics, the low frequency component is greatly attenuated and the DC component is completely suppressed. Furthermore, phase distortion occurs over the entire band. Therefore, since the equalizer 52 is mainly configured to correct various losses in the high frequency component, the output waveform of the equalizer 52 is a waveform 59. When the direct current component and low frequency component of the tape head system are completely corrected by the integrator 53, the integrated output shown in waveform 60 is obtained, but due to various factors, deterioration remains in the direct current component and low frequency component. In reality, the output of the integrator 53 is as shown by the waveform 62. With respect to the ideal integrated waveform 60, if "0" and "1" are discriminated depending on whether or not the threshold value 61 is exceeded, a waveform 58 that is the output of the modulator 48 is obtained. However, in reality, the detector 54 discriminates between “0” and “1” depending on whether or not the waveform 62 exceeds the threshold value 63, so that the result is the waveform 64 and the waveform 58.
The detection timing error is 65 to 67 because it is significantly different from.

Problems to be Solved by the Invention As described above, if the direct current component or the low frequency component in the tape head system is deteriorated, the above error occurs in the detector 54. On the other hand, in FIG. 6, various noises and intersymbol interferences are all omitted for simplification of description. However, as a result of superposition of these noises and intersymbol interferences, the above-mentioned deterioration is It is an increase in extreme mistakes.

Further, in the conventional method shown in FIGS. 5 and 6, the integral detection is performed. However, in the amplitude detection or the like, the error sharply increases due to the amplitude variation due to the change of the space loss between the tape head and the like. To do.

Therefore, the present invention significantly reduces the detection error due to the deterioration of the DC component and the low frequency component and the detection error due to the amplitude variation.

Means for Solving the Problems In order to reduce such detection error, the present invention provides a positive peak detector for detecting a positive peak value of a reproduction signal input to the detector, and a positive peak value thereof. , And a negative filter that detects the negative peak value of the reproduced signal, and a local change of the negative peak value. A low-pass filter that passes only the low-frequency component of the negative peak, a threshold generator that creates a threshold value based on the outputs of both low-pass filters, the above-mentioned reproduced signal and the threshold value created by this threshold value generator. And a comparator that obtains a detection output by comparison.

By providing such means, fluctuations in DC level due to deterioration of DC components and low-frequency components as described above, and amplitude fluctuations due to variations in space loss between tape heads, etc. occur. However, the detection threshold value can always be automatically corrected to an ideal value.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an input terminal, 2 is a positive peak detector, 3 is a low pass filter (LPF), 4 is a negative peak detector, 5
Is a low pass filter (LPF), 6 is a threshold generator, 7 is a comparator,
8 is an output terminal. The output of the equalizer of the reproduction system is input terminal 1
It is input to the positive peak detector 2, the negative peak detector 4 and the comparator 7 via. The positive peak detector 2 detects the positive peak value of the input signal, and the negative peak detector 4 detects the negative peak value of the input signal. The positive peak detector 2 and the negative peak detector 4 are configured to detect a maximum value and a minimum value, for example. The output of the positive peak detector 2 is applied to the low pass filter 3, and the output of the negative peak detector 4 is applied to the low pass filter 5. The low-pass filters 3 and 5 eliminate the local fluctuations in the outputs of the positive peak detector 2 and the negative peak detector 4 and derive the relatively long-term tendency of both peaks. The threshold value generator 6 creates a threshold value based on the outputs of both the low-pass filters 3 and 5. The output of the threshold generator 6 and the signal applied through the input terminal 1 are compared by the comparator 7, and the detected output is sent out through the output terminal 8.

FIG. 2 is a waveform diagram showing the state of each part of FIG. In the figure, 9 is the output data string of the modulator, waveform 10 is the waveform of the data string 9, waveform 11 is the output waveform of the integrator, 12-14 are positive peak values, 15-17 are negative peak values, and the broken line 18 and 19 are output waveforms of the low-pass filters 3 and 5, respectively, and a chain line 20 is a threshold value. This embodiment shows the case where NRZ is used as the modulation method and the integration method is used as the detection method on the reproducing side. When the data string to be recorded is 9, the recording waveform is waveform 10. On the other hand, on the reproducing side, the signal that has passed through the equalizer and the integrator has a waveform 11, and the direct current level varies depending on the data pattern due to the deterioration of the direct current component and the low frequency component. Positive peak detector 2 has positive peak potentials 12, 13, 14 ...
, And the negative peak detector 4 detects the negative peak potentials 15, 16, 17, .... The positive peak potentials 12, 13, 14, ... Pass through the low-pass filter 3 and become a broken line 18, and the negative peak potentials 15, 16, 17 ,. The threshold generator 6 calculates the average value of the broken lines 18 and 19 which are the outputs of the low-pass filters 3 and 5 to generate a threshold waveform (dotted line) 20. The dashed-dotted line 20 is a waveform
It is located at the midpoint between the positive peak potential and the negative peak potential following the DC level fluctuation of 11. Since the comparator 7 compares the voltage between the waveform 11 and the one-dot chain line 20 which is the threshold value, the detection output sent from the output terminal 8 is equal to the waveform 10 and does not include the detection error due to the DC level fluctuation. Of course, the embodiment of the invention shown in FIG. 1 is inserted as detector 54 in FIG. 5, for example.

The case where the present invention is applied to the system of the combination of NRZ modulation and integral detection has been described above.Next, the case where the present invention is applied to a system employing NRZI as the modulation method and amplitude detection as the detection method will be described below. To do.

FIG. 3 is a block diagram showing a part of a digital recording / reproducing apparatus in the case of a combination of NRZI modulation and amplitude detection.
In the figure, 37 is a data input terminal, 38 is an NRZI modulator,
39 and 41 are magnetic heads, 40 is magnetic tape, 42 is an equalizer,
43 is a detector and 44 is a data output terminal. The data string after digital signal processing is input via the data input terminal 37.
It is applied to the NRZI modulator 38. It goes without saying that NRZI inverts its output level every time "1" appears in the input data string. The output of the NRZI modulator 38 is recorded on the magnetic tape 40 via the magnetic bed 39. At the time of reproduction, the information recorded on the magnetic tape 40 is read by the magnetic head.
It is read out via 41, equalized by an equalizer 42, and then applied to a detector 43. The detector 43 is for amplitude detection, and sends the detection result to the digital signal processing system via the data output terminal 44.

Next, another embodiment of the present invention used as the detector 43 in FIG. 3 is shown in a block diagram in FIG. In FIG. 4, 1 to 6 are the same as 1 to 6 in FIG. 1, and therefore their description is omitted. 7a and 7b are comparators, 45 is an OR gate (“OR gate”), and 46 is an output terminal. The output of the equalizer 42 of FIG. 3 is applied via the input terminal 1. Positive peak detector 2, low pass filter 3, negative peak detector 4 and low pass filter 5 perform the same operations as 1-5 in FIG. The threshold generator 6 creates two thresholds based on the outputs of both the low pass filters 3 and 5. The two threshold values are respectively coupled to one input terminals of the comparators 7a and 7b, and the signal applied to the input terminal 1 is coupled to the other input terminals of the comparators 7a and 7b.
In each of the comparators 7a and 7b, the result of the voltage comparison between the signal applied through the input terminal 1 and the respective threshold value is supplied to the OR gate 45. The OR gate 45 ORs the outputs of both comparators 7a and 7b and sends the detection result via the output terminal 46.

FIG. 2 also shows the state of each part in the other embodiment of the present invention shown in FIGS. 3 and 4, in which the waveform 21 has no amplitude fluctuation. The output waveform of the equalizer 42, the waveform 22 is the output waveform of the equalizer 42 when amplitude fluctuation is accompanied, 23, 24, 25 ... are positive peak values, 26, 27, 28
...... is the negative peak value, the broken line 29 is the output waveform of the low-pass filter 3,
The broken line 30 is the output waveform of the low-pass filter 5, the alternate long and short dash line 31 is the threshold value created by the threshold value generator 6 and input to the comparator 7a, and the alternate long and short dash line
32 is the threshold value created by the threshold value generator 6 and input to the comparator 7b, period 33 is the period during which the amplitude is changing, waveform 34 is the output waveform of the OR gate 45, 35 is the reproduction clock timing, and 36 is the waveform 34 It is the waveform sampled and held at the clock timing 35 (actually the latch output after the waveform 34 is input to the latch and triggered by the waveform 35). It is assumed that the NRZI-modulated data string has 9 waveforms.

In the amplitude detection, the fluctuation in the amplitude greatly increases the error more than the deterioration in the direct current component and the low frequency component among the deteriorations in the tape head system. The reason is that the threshold at the time of detection does not have to be set to the center level of the signal as in integral detection, but rather to a predetermined value between the center level of the signal and the peak level. Is because it deviates from the optimum value. However, in the embodiment of the present invention shown in FIG. 4, the output of the low-pass filter 3 is the broken line 29.
In addition, the output of the low-pass filter 5 is a broken line 30, which follows the fluctuation of the peak value. In addition, the threshold generator 6 creates two thresholds V ₊ and V ₋ represented by the following equation.

V ₊ = (3 ・ P ₊ ＋ P ₋ ) / 4 …… (1) V ₋ ＝ (P ₊ ＋3 ・ P ₋ ) / 4 …… (2) (where P ₊ is the output potential of the low pass filter 3) , P ₋ is the output potential of the low-pass filter 5.) In this way, V ₊ is the waveform 22
Is always set to the midpoint between the central level and the positive peak of, V _- the central level and the one-dot chain line 31 V ₊ so always set to the midpoint between the negative peak of the waveform 22, V _- the chain line 32 Equivalent to.
V ₊ is applied to the comparator 7a and V ₋ is applied to the comparator 7b, and the comparator 7a outputs a high level only during a period when the potential of the waveform 22 is high with respect to the alternate long and short dash line 31 which is V ₊ . In 7b, the high level is output only during the period when the potential of the waveform 22 is low with respect to the alternate long and short dash line 32 which is V ₋ . The outputs of both comparators 7a and 7b are logically ORed by an OR gate 45 and a waveform 34 is output. OR gate 45
When the output of is sample-held at the reproduction clock timing 35, a waveform 36 is obtained, which is equivalent to the waveform 10 demodulated by NRZI. In this way, the dashed-dotted line, which is the threshold for detection, despite the occurrence of amplitude fluctuations in period 33
31 and 32 are always automatically corrected to the ideal value by following the amplitude fluctuation.

Although the present invention has been described above with reference to two embodiments, the present invention is not limited to a digital data recording / reproducing apparatus using a magnetic tape as a recording medium, but a digital recording / reproducing apparatus using another recording medium. Can also be applied.
Furthermore, the present detection method is not limited to the digital data recording / reproducing apparatus, but can be applied to a digital data transmitting apparatus.

However, the effect of the present invention is very large in a digital data recording / reproducing apparatus which is required to have an extremely high recording density such as a digital VTR.

In this description, the case of the combination of NRZ and integral detection and the case of NRZI
However, the present invention can also be applied to spawning and multilevel recording as a detection method.

EFFECTS OF THE INVENTION As is clear from the above description, the present invention is capable of reducing fluctuations in DC level caused by deterioration of DC components and low-frequency components in the tape head system and space loss between the tape heads. Even when there is a change in the amplitude caused by a change or the like, the detection threshold value is automatically corrected so as to always have an ideal value. As a result, the combination of the NRZ modulation method and integral detection or amplitude detection even in a transmission line (or recording / playback system) where the DC component and low-frequency component are deteriorated and the amplitude fluctuation is severe, as when using a magnetic tape as the recording medium. Is possible. Therefore, the advantages of the NRZ system can be taken advantage of and the drawbacks can be ameliorated, so that higher density recording becomes possible and at the same time the frequency of error occurrence can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram showing the state of each part in FIGS. 1, 3, and 4, FIG. 3 and FIG. 4 are block diagrams showing a second embodiment of the present invention, and FIG. The block diagram shown in FIG. 6 and FIG. 6 are waveform diagrams showing the states of the respective portions in FIG. 2 ... Positive peak detector, 3 ... Low-pass filter, 4 ... Negative peak detector, 5 ... Low-pass filter, 6 ... Threshold generator, 7,
7a, 7b …… Comparator, 45 …… OR gate.

Claims (1)

[Claims] 1. A positive peak detector for detecting a positive peak value of a detected signal, a negative peak detector for detecting a negative peak value of the detected signal, and an output of the positive peak detector in a low range. A first low-pass filter for filtering, a second low-pass filter for low-pass filtering the output of the negative peak detector, an output of the second low-pass filter and the first low-pass filtering Of a digital signal characterized by comprising a threshold value generator for creating a threshold value based on the output of the comparator, and a comparator for performing a potential comparison between the threshold value and the signal, and using the output of the comparator as a detection output. Detection device.