JPS63217712A - Digital information reproducing device - Google Patents

Abstract

PURPOSE:To obtain a normal digital signal by providing a means passing a low fre quency component being a difference between a recovered digital signal being the result of waveform shaping of an input signal and an information signal synchronizing the signal by a read clock in parallel with a conventional device so as to suppress a noise in an original signal up to the low frequency band. CONSTITUTION:The characteristic of a 1st LPF3 and a 2nd LPF4 is selected by selecting component so as to correspond to the low frequency noise suppression and the high frequency noise suppression respectively. In this case, the closed circuit formed through the LPF 3 realizes the DC slice system to suppress the noise of a frequency lower than the low frequency component of the original signal. The closed circuit through the LPF 4 extracts a low frequency component being the difference between the recovered digital signal and the information signal synchronized by using a read clock and it is used as threshold value control information. In the AC slicing, the low frequency spectrum of the original signal is subject to less suppression than that of the high frequency noise. Thus, the DC and AC slice circuits are connected in parallel and the operating region of the closed circuit is divided to suppress the noise signal of up to low frequency spectrum.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital information reproducing device that reads information from a digital signal that has passed through a transmission path with a limited band, and particularly to a waveform shaping device that reads the digital signal correctly. The present invention relates to a digital information reproducing device that can control a threshold value.

2. Description of the Related Art In recent years, in order to transmit or record digital signals at high density, it has become common practice to transmit or record digital signals in the baseband. In this case, it is necessary to waveform shape the transmitted signal using a predetermined threshold value. However, there is a problem in that the optimal threshold value fluctuates because low frequency noise is likely to be mixed into the signal due to temperature drift of the circuit, unevenness of the recording medium, or fingerprints attached to the recording medium. Therefore, in order to eliminate the influence of threshold fluctuations caused by such low-frequency noise, there is already a method of integrating a digital signal obtained by waveform shaping an input signal containing noise and controlling the threshold according to the result. It is publicly known. Furthermore, in order to efficiently suppress the effects of low frequency noise using the above method, a modulation method that does not include a DC component in the signal is often used. −
For example, EFM (Eight to Fourteen Mo.
duration), etc.

An example of the above-mentioned conventional digital information reproducing device will be described below with reference to the drawings.

FIGS. 4 and 5 are block diagrams of the main parts of a conventional digital information reproducing apparatus and a conceptual diagram of its operation. In FIG. 4, reference numeral 1 denotes a waveform shaping means which shapes the waveform of an input signal at a predetermined threshold value and outputs a reproduced digital signal. Reference numeral 2 denotes a D free knob flop, which constitutes synchronization means for reading the reproduced digital signal, latching it with a clock, and outputting a data signal. 5 is an operational amplifier.

Reference numeral 8 denotes an integrator which negatively feeds back the low-frequency component of the reproduced digital signal to the waveform shaping means to generate a predetermined threshold value.

7 is a clock extracting means which extracts a read clock from the reproduced digital signal. FIG. 5 is a diagram showing the operational concept of FIG. 4.

The operation of the conventional digital information reproducing apparatus configured as described above will be explained below.

First, the waveform shaping means 1 shapes the waveform of an input signal using the output of the integrator 8 as a threshold value, and outputs a reproduced digital signal. However, the input signal is assumed to consist of an original signal modulated using a modulation method that does not include a DC component, and a low-frequency noise signal having a frequency lower than the low-frequency components of the original signal. An integrator 8 is used to suppress the low-frequency noise signal from the input signal and extract only the digital signal contained in the original signal.

This suppression operation will be explained using FIG. 5. The waveform marked as reproduced signal in FIG. 5 corresponds to the above input signal. In the figure, to simplify the explanation,
The original signal is assumed to be a sine wave containing no DC component, and the low-frequency noise signal is assumed to have a waveform with a correct threshold value.

When the input signal synthesized from the two types of waveforms described above is waveform-shaped using a constant potential, for example, a threshold value based on the ground potential, waveform B in the figure is obtained. As is clear from this waveform, jitter occurs in the digital signal after waveform shaping due to low-frequency noise components.

In order to avoid this, it is necessary to waveform-shape the reproduced signal shown in the figure with a waveform marked with the correct threshold value.

In order to find this correct threshold value, integrator 8 is shown in FIG.
is used. It can be easily seen that when the reproduced signal in FIG. 5 is integrated, the shaded portion cancels out and only the waveform of the correct threshold value remains.

However, since the integrator 8 is of a polarity inversion type, it is assumed here that the waveform shaping means 1 includes means for adjusting the polarity. When the waveform shaping means 1 shapes the waveform using the correct threshold value extracted by the integrator 8 in FIG. 4, the waveform A shown in FIG.
(See Publication No. 1).

Hereinafter, the digital signal shaping method shown in FIG. 4 will be referred to as the DC slice method.

Generally, the original signal does not become a sine wave with a single frequency, but has a waveform that is a combination of multiple sine waves, but when a DC-free modulation method is used, the above-mentioned noise suppression principle can be applied as is. Generally, in order to digitally handle the signal in an electric circuit connected to a subsequent stage of the digital information reproducing device, a reference clock is extracted from the reproduced digital signal by the clock extracting means 7 and the synchronizing means 2
Synchronize the reproduced digital signals using

Problems to be Solved by the Invention However, with the above configuration, operation is possible only when the low-frequency noise component is lower than the low-frequency component of the original signal; The problem is that if noise is mixed in, it cannot be suppressed.

In view of the above-mentioned problems, the present invention provides a digital information reproducing device that can suppress the noise mixed in the input signal and shape the normal digital signal even when the noise extends to the low frequency band of the original signal. It is something.

Means for Solving the Problems In order to solve the above problems, the digital information reproducing apparatus of the present invention includes a waveform shaping means for outputting a reproduced digital signal by shaping the waveform of a human signal at a predetermined threshold; a first threshold error detection means for substantially negatively feeding back the low-frequency noise component of the reproduced digital signal; It is equipped with a second threshold error detection means that substantially provides negative feedback of the loud noise components.

According to the above-described configuration, the present invention can separate the low-frequency noise signal included in the waveform-shaped digital signal into noise lower than the band of the original signal and noise overlapping the band of the original signal, and extract the components thereof. .

As a result, even if the noise mixed in the input signal extends to the low frequency band of the original signal, the noise can be suppressed and a normal digital signal can be shaped.

Embodiment Hereinafter, a digital information reproducing apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the main parts of a digital information reproducing apparatus in an embodiment of the present invention. In FIG. 1, ``■'' is a waveform shaping means that shapes the waveform of a human input signal and outputs a reproduced digital signal. Reference numeral 2 denotes a D flip-flop, which constitutes synchronization means for reading the reproduced digital signal, latching it with a clock, and outputting a data signal.

3 is a first low-pass filter that extracts low-frequency components of the digital signal. Reference numeral 4 denotes a second low-pass filter that extracts the low-frequency component of the signal consisting of the difference between the reproduced digital signal and the data signal. 5 is an operational amplifier, and 6 is a buffer for analog operation. 7 is a clock extracting means which extracts a read clock from the reproduced digital signal. operational amplifier 5
．． The buffer 6, the resistance element, and the DC voltage source constitute an analog signal addition means, the output of which is a threshold control output.

The operation of the digital information reproducing apparatus configured as described above will be explained below with reference to FIGS. 1, 2, and 3.

First, FIG. 2 shows a noise spectrum due to fingerprints, which is one of the noises that may occur when the digital information reproducing apparatus of this embodiment is used as a compact disc reproducing apparatus. It has been confirmed that noise caused by fingerprints has large amplitudes at two locations in the low frequency spectrum of the original signal, as shown in the figure. Of these two noises, the low-frequency noise that exists in the lower frequency region can be suppressed by the DC slice method, which is a conventional threshold control method. However, among the above-mentioned noises, high-frequency noise that exists in a high frequency region cannot be suppressed by the DC slice method. For example, if the characteristics of the integrator 8 are changed to a higher frequency in the configuration shown in Fig. 4, high-frequency noise is certainly suppressed, but at the same time, the low-frequency spectrum included in the original signal is also removed, and as a result, a normal digital signal is You won't be able to get it. This is as described in the problem to be solved by the invention.

Therefore, in order to avoid this, in this embodiment, as shown in FIG. 1, in addition to the conventional configuration, a second low-pass filter 4 for suppressing high-frequency noise shown in FIG. 2 is newly provided.

In FIG. 1, the characteristics of the first low-pass filter 3 and the second low-pass filter 4 are shown in FIG. Element values are selected to correspond to the pass filter characteristics. At this time, the closed circuit formed through the first low-pass filter 3 realizes the conventional DC slice method described in FIG. At this time, the DC slice controls the threshold value so as to suppress noise at a frequency lower than the low frequency component of the original signal, that is, the low frequency noise shown in FIG. 2. On the other hand, the second low-pass filter 4 controls the threshold value so as to mainly suppress the high-frequency noise shown in FIG. 2. As realized by a closed circuit formed through the second low-pass filter 4, the low frequency component of the signal consisting of the difference between the reproduced digital signal and the data signal obtained by reading the reproduced digital signal and synchronizing it with a clock is extracted. , the method of using this as information for threshold control will hereinafter be referred to as AC slice. A.C.
The slice responds to and removes not only the high-frequency noise shown in FIG. 2 but also the low-frequency spectrum of the original signal.

However, if the low-frequency spectrum is removed from the original signal, a large threshold fluctuation (AC
The low frequency spectrum of the original signal is suppressed to a lesser extent than the high frequency noise.

In this way, by connecting the circuits that realize DC slice and AC slice in parallel and dividing the frequency range in which each closed circuit operates, noise that extends to the low frequency spectrum of the original signal as shown in Figure 2 can be reduced. The signal can be suppressed. However, as the characteristics of the two types of low-pass filters are shown in FIG. 3, the low-pass filter for low-frequency noise suppression must have a sufficiently larger gain than the other in the vicinity of DC.

Further, the characteristics shown in FIG. 3 must be directly reflected in the round transfer function of a closed circuit that realizes a DC slice and the round transfer function of a closed circuit that realizes an AC slice.

As described above, according to this embodiment, the second low frequency component passes the low-frequency component of the difference between the reproduced digital signal obtained by shaping the input signal and the data signal obtained by reading this reproduced digital signal and synchronizing it with the clock. By providing the band pass means in parallel with the conventional configuration method, it is possible to suppress noise in the low frequency components of the original signal, which could not be suppressed in the conventional method.

Note that in the embodiment, there are no restrictions on the orders of the first and second low-pass filters. Also, active elements may be used.

For example, in order to take the difference between the reproduced digital signal and the data signal, the second low-pass filter 4 uses a resistive voltage divider, but it is also possible to perform subtraction using an active circuit and then pass the signal through a single-handed low-pass filter. Furthermore, since the pull-in characteristics of the two types of closed circuits (DC slice loop and AC slice loop) differ depending on the shape of the input signal, the characteristics shown in FIG. 3 are not necessarily optimal. Therefore, the characteristics of the filter must be optimized depending on the case.

Further, in the embodiment, the clock extracting means 7 is used to obtain a synchronized data signal, but instead of this, a suitable reference clock may be supplied from outside.

Effects of the Invention As described above, the present invention provides a second low-frequency component that passes the low-frequency component of the difference between the reproduced digital signal obtained by shaping the input signal and the data signal obtained by reading this digital signal and synchronizing it with a clock. By providing the passing means in parallel with the conventional configuration method, it is possible to suppress noise in the low frequency components of the original signal, which could not be suppressed in the conventional method.

Particularly when the present invention is used in a playback device for a compact disc device, it is possible to suppress noise in a band that could not be completely removed in the past.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of a digital information reproducing device according to an embodiment of the present invention, and FIG. 2 is a frequency characteristic diagram of noise caused by fingerprints in a compact disc device that is a target of suppression according to an embodiment of the present invention. FIG. 3 is a frequency characteristic diagram of two types of low-pass filters used in the first embodiment of the present invention, FIG. 4 is a block diagram of the main parts of a conventional digital information reproducing device, and FIG. FIG. 2 is an operational conceptual diagram for explaining the block diagram in the figure. ■...Waveform shaping means, 2...Synchronization means, 3...First low-pass filter, 4...
. . . second low-pass filter, 5 . . . operational amplifier, 6. old hasha sofa, 7 .

Claims (2)

[Claims] (1) A waveform shaping means for shaping an input signal at a predetermined threshold value and outputting a reproduced digital signal; and a threshold control means for controlling the predetermined threshold value; The control means includes a first threshold error detection means for detecting a threshold error by substantially comparing the low frequency component of the reproduced digital signal with a predetermined value, and a first threshold error detection means for detecting a threshold error by substantially comparing the low frequency component of the reproduced digital signal with a predetermined value; a second threshold error detection means for detecting a threshold error from the reproduced digital signal substantially with reference to a clock; and a sum of the outputs of the first and second threshold error detection means. the first threshold error at a frequency where the round transfer function of the control loop including the second threshold error detection means is 1; The loop transfer function of the control loop including the detection means is smaller than 1, and the loop transfer function of the control loop including the second threshold error detection means in DC is smaller than one loop of the control loop including the first threshold error detection means. A digital information reproducing device characterized in that it is configured to be smaller than a transfer function. (2) The first threshold error detection means realizes this by inputting the reproduced digital signal waveform-shaped with a predetermined threshold value to the first low-pass filter, and detects the second threshold error. The detection means inputs into the second low-pass filter a signal consisting of a difference between a signal obtained by synchronizing the reproduced digital signal with a read clock indicating the timing of reading information and a reproduced digital signal whose waveform has been shaped by a predetermined threshold value. This is achieved by
and the output of the second low-pass filter are added at a predetermined ratio, and this output is used as the predetermined threshold for waveform shaping. Information reproducing device.