JPS60193171A - Reproducing circuit of digital signal - Google Patents

Abstract

PURPOSE:To prevent generation of a transient state without losing a low frequency component of a reproducing signal by providing a switching means controlled by a control signal so that a time constant including a coupling capacitor is increased more after a nearly transient period from a point of time when the period is switched from a period with no digital reproducing signal into a period having the said signal. CONSTITUTION:A band pass filter 10, an envelope detection circuit 11, a comparator 12 and a delay circuit 14 constitute a detection circuit detecting the presence or absence of the digital reproducing signal from an input terminal 1. A detected output as shown in Fig. B is generated from the envelope detection circuit 11 in response to the digital reproducing signal as shown in Fig. A. When the detected output is given through the comparator 12 and the delay circuit 14, a control signal as shown in Fig. C is formed and this control signal is fed to a switching circuit 7. When the control signal is at high level, the switching circuit 8 is turned on and when the control signal is at low level, the switching circuit 7 is turned off. Thus, the switching circuit is turned from on to off after a time T from the point of time when the period is switched from a period without any digital reproducing signal to a period having it in case of the control signal as shown in Fig. C.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a digital signal reproducing circuit applied to a reproducing circuit for recordable optical discs.

"Background technology and its problems" For example, in a recordable optical disc used in a document file device, address signals are recorded on the track in advance, and the user writes digital data into the data section after each address signal. be made to record. - For example, an address signal is recorded by the presence or absence of a bit on an optical disc,
Data is recorded as changes in the reflectance of the signal surface of the optical disc.

In such recordable optical discs, there is no guarantee that there will be no empty space in the data section and digital data will be recorded;
As shown in FIG. A, the reproduction signal of the disc becomes an intermittent signal in which sections with and without signals are mixed. A reproduced signal read from the disk by the optical head is supplied to a slicing circuit via a coupling capacitor, and taken out as a pulse signal at the output of this slicing circuit.

It is desirable that the time constant including this coupling capacitor be as small as possible. The reason is that when the time constant is large, when the reproduced signal shown in Figure 4A passes through the time constant circuit,
This is because, as shown in FIG. 2, transients occur where the DC level fluctuates greatly, and when the slicing circuit performs slicing, malfunctions occur due to errors in signal output and processing. As mentioned above, when an address signal is pre-recorded on an optical disc, as shown in FIG. 5A, the playback signal becomes a signal where the address signal is at a much lower level than the data, and in the case of FIG. The fluctuations in the DC level become larger. Therefore, when the time constant of AC coupling is large, a large transient occurs as shown in FIG. 5B.

If the time constant of the AC coupling is made small in order to suppress the transients, when the occupied frequency band of the digital reproduction signal extends to low frequencies, negative effects such as code amount interference due to the cutting of low frequency components will occur, resulting in the reproduction This makes it difficult to faithfully transmit the signal waveform.

"Objective of the Invention" Therefore, the object of the present invention is to produce a digital reproduction signal without damaging the low frequency components! - It is an object of the present invention to provide a digital signal reproducing circuit that can prevent the occurrence of transients and prevent malfunctions in the next-stage slice processing.

"Summary of the Invention" The present invention provides a digital signal reproducing circuit in which a coupling capacitor is inserted between an input terminal to which a digital reproduced signal is supplied and a slice circuit, which generates a control signal depending on the presence or absence of a digital reproduced signal. and a switching means that is controlled by a control signal so as to increase the time constant including the coupling capacitor approximately after the transient period from the time when the digital reproduction signal switches from the period in which there is no digital reproduction signal to the period in which it exists. This is a digital signal reproducing circuit.

"Embodiment" An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 indicates an input terminal for a reproduction signal from an optical disc, and 2 and 3 indicate buffer circuits. The input terminal 1 is connected to a buffer circuit 2, and the output terminal of the buffer circuit 2 is connected to a buffer circuit 30 via a coupling capacitor 4.
Connected to the input terminal. A resistor 5 and a resistor 6 are connected between the connection point of the coupling capacitor 4 and the input terminal of the buffer circuit 30 and the ground.
and a series connection of switching circuits γ are inserted in parallel. The output terminal of the buffer circuit 3 is supplied to the slice circuit 8. The slicing circuit 8 slices the output signal of the buffer circuit 3 at a predetermined level, and a digital reproduction signal in the form of a pulse signal is obtained at its output terminal 9.

The input terminal 1 and the buffer circuit 2 are connected to a bandpass filter 10 with f? It will be covered. The output of the bandpass filter 10 is supplied to an envelope detection circuit 11. The output of this envelope detection circuit 11 is supplied to a humpator 12 and compared with a reference voltage 13. The detected output of the Stetsuzo waveform obtained from the output of the comparator 12 is supplied to the switching circuit 1 as its control signal via the delay circuit 14 for timing adjustment.

The above-mentioned bandpass filter 10, envelope detection circuit 11, comparator 12, and delay circuit 14 are connected to the input terminal 1.
A detection circuit is configured to detect the presence or absence of a digital reproduction signal from. The passband of Pandopa's Fi, Luta 10 is
This corresponds to the band of the digital reproduction signal, and noise outside this band is removed by the bandpass filter 10. When there is a digital reproduction signal, the output signal of the comparator 12 is high level, and when there is no digital reproduction signal, the output signal of the comparator 12 is low level. The delay circuit 14 is provided to turn the switching circuit 7 from an on state to an off state approximately after a transient period from the point in time when the digital reproduction signal is switched from a period in which there is no digital reproduction signal to a period in which it is present. Instead of providing the delay circuit 14, the level of the reference voltage 130 of the comparator 12 may be increased to cause a delay.

One track of an optical disk is divided into two, for example, into 20 sectors (0 to 19), as shown in FIG. 2A. Data is written and read in units of sectors. Each sector includes an address part and a data part, as shown in FIG. 2B. An address section is recorded in advance on the optical disc by its manufacturer. Furthermore, a synchronization signal is recorded at the beginning of each of the address section and the data section. This synchronization signal is a pulse signal with a repetition frequency equal to the highest frequency of the channel-modulated recording signal. If the length of one sector is, for example, 1.5 bytes, the synchronization signal is approximately 16 bytes long.

In the above-described embodiment of the present invention, the operation when a digital reproduction signal is supplied from the input terminal 1 that switches from an interval without a signal to an interval with a signal as shown in FIG. 3A will be described. The section without this signal may be an address section, and the section with a signal is a data section, and the synchronization signal is located at the beginning of the data section. As described above, since the address part is recorded in advance as the presence or absence of bits, the reproduced signal of the address part has a lower level than the reproduced signal of the data part. . However, by providing the bandpass filter 10, the reproduced signal of the address section and the reproduced signal of the data section are made into signals of the same DC level and supplied to the envelope detection circuit 11.

Corresponding to the digital reproduction signal shown in FIG. 3A, the envelope detection circuit 11 generates a detection output shown in FIG. 3B. By passing this detection output through the comparator 12 and the delay circuit 14, a control signal shown in FIG. 3C is formed, and this control signal is supplied to the switching circuit γ. When the control signal is at a high level, the switching circuit 7 is turned on, and when the control signal is at a low level, the switching circuit 7 is turned off. Therefore, in the case of the control signal shown in FIG. 3C, the switching circuit 7 is turned off from ON after time T has elapsed from the point in time when the digital reproduction signal is switched from the period without it to the period with it.

When switching circuit γ is ON, resistor 5 and resistor 6
The time constant τ1 of AC coupling is determined by the parallel resistance value of , and the coupling capacitor 4, and the time constant τ2 of AC coupling is determined by the resistor 5 and the coupling capacitor 4 when the switching circuit 7 is in the OFF state. Therefore, (τ1<τ2). In a section where there is no signal, even if the time constant τ is small, low frequency components are canted, and waveform deterioration due to code amount interference etc. does not become a problem.

Furthermore, since the time constant τl is small even in the first period T of the section where the signal exists, it is possible to prevent a large transient from occurring within this period T.

However, since the digital reproduction signal during this period T is a synchronizing signal with a high frequency, even if the time constant τ1 is small, the waveform does not deteriorate. Then, after the period T after the transient period, the time constant τ2 becomes large, so that the reproduced signal is supplied to the slice circuit 9 without waveform deterioration.

Although not shown in FIG. 3, when changing from a period with a signal to a period without a signal, the control signal rises from low level to high level, and the switching circuit 7 changes from the OFF state to the OFF state.
It becomes N state. Therefore, the large time constant τ2 is switched to the small time constant τ1.

When switching from a section where this signal is present to a section where it is not present, the adverse effects of transients are small and a large time constant τ2 may be used.

Unlike the above embodiment, the control signal of the switching circuit T is formed by detecting the start and end of reading the digital reproduction signal on the output side of the slice circuit 8, without using the envelope detection circuit. You can do it like this. Furthermore, the slice circuit 8 may be configured to vary the reference level.

"Effects of the Invention" According to the present invention, even if the digital reproduction signal is intermittent or includes address signals and data, such as the reproduction signal of a recordable optical disc, the transient 1- can be made small, malfunctions of the slice circuit can be prevented, and the waveform of the reproduced signal can be faithfully transmitted. According to the present invention, invalid sections such as synchronization signal sections for transient absorption can be reduced, and recording or transmission speed and density can be increased.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of an embodiment of this invention, Fig. 2 is a route diagram used to explain the data structure in an embodiment of this invention, and Fig. 3 is a waveform used to explain the operation of an embodiment of this invention. 4 and 5 are waveform diagrams used to explain a conventional digital signal reproducing circuit. 1... Input terminal, 2, 3...
...Buffer circuit, 4...Coupling capacitor, 7...Switching circuit, 8...
・・・・・・Slice circuit, 9・・・・・・・・・Output terminal, 11・・・・・・Envelope detection circuit. Agent: Tomo Sugiura Figure 1 Figure 3 Figure 4 ■ Figure 5

Claims (1)

[Claims] In a digital signal reproducing circuit in which a coupling capacitor is inserted between an input terminal to which a digital reproduction signal is supplied and a slice circuit, the circuit generates a control signal depending on the presence or absence of the digital reproduction signal; a digital signal comprising a switching means controlled by the control signal so as to increase a time constant including the coupling capacitor substantially after the transient period from the point in time when switching from a period without a signal to a period with a signal; regeneration circuit.