JPH06162516A - Reproduced signal processing circuit - Google Patents

Abstract

PURPOSE:To provide a reproduced signal processing circuit in which a cutoff frequency of a differentiating circuit that differentiates reproduced signals is suppressed even though the maximum basic frequency of the reproduced signals of an optical information recording medium is relatively high without degrading the S/N and the information is accurately reproduced. CONSTITUTION:The following means are provided, i.e., a photoelectric detecting means which outputs reproduced beams from an optical information recording medium as electrical signals, a differentiating means 4 which differentiates the electrical signals, a zero cross detecting means 5 which detects the zero crossing of output signals of the means 4, a gate signal generating means 6 which generates gate signals by level slicing the electrical signals of the photoelectric detecting means, a delaying means 8 which delays the gate signals and a gate circuit means which outputs information output signals by gating the output signals of the means 5 by the gate signals that are delayed by the delaying means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for processing a reproduced signal from an optical information recording medium.

[0002]

2. Description of the Related Art In a conventional optical information recording / reproducing system, when demodulating information recorded in a pit position recording system on an optical disk or the like as an optical information recording medium,
In order to detect the peak position of the reproduction signal obtained by photoelectrically detecting the reproduction beam from the medium, a method of differentiating the reproduction signal and finding the zero-cross point of the differentiation signal is generally used. In this method, the maximum fundamental frequency of the reproduced signal is relatively low (for example, an optical disc with a diameter of 130 mm is
When rotating at 800 rpm, if the maximum fundamental frequency a 3.7MH _Z) of the ISO standard referred to as cut-off frequency (below the cut-off frequency of the differentiation circuit composed of the CR circuit or the like)
The by setting approximately 10-fold (37MH _Z) degree of maximum fundamental frequency, it was possible to detect the peak position of precisely the corresponding reproduced signal to the recording information.

FIG. 3 is a block diagram showing a conventional reproduction signal processing circuit. As shown in FIG. 3, the conventional reproduction signal processing circuit includes an information recording medium 11, a photodetector 12, a photoelectric converter 13, a differentiation circuit (high-pass filter) 14, a zero-cross detection circuit 15, a gate signal generation circuit 16, and an AND circuit. It was mainly composed of the circuit 17. Note that (a) to (g) shown in FIG. 4 show output waveforms of respective parts in the conventional reproduction signal processing circuit shown in FIG. 3, and the horizontal axis is a time axis.

As shown in FIGS. 3 and 4, the information signal (b) obtained from the information recording medium 11 through the photodetector 12 and the photoelectric converter 13 is input to the differentiating circuit 14 and the gate signal generating circuit 16. To be done. An output signal (c) of a differential waveform of the information signal (b) is generated from the differentiating circuit 14, and a zero cross point in the differential waveform of the signal (c) is detected by a zero cross detecting circuit 15 including a comparator,
The zero-cross signal (d) is input to one input terminal of the AND circuit 17. The black dots in FIG. 4C are information points, and N in (d) is the zero-cross signal (d).
The noise that springs up is shown.

On the other hand, the gate signal generating circuit 16 uses the level slice from the information signal (b) to generate the gate signal (e).
Is created, and this is input to the other input terminal of the AND circuit 17.

The AND circuit 17 is a zero cross detection circuit 1.
The zero-cross signal (d) output from No. 5 is gated by the gate signal (e) output from the gate-signal creating circuit 16 to remove the noise N generated from the zero-cross signal (d), and the rising position (arrow position). ) Is output as an information signal (g). In this case, a high-pass filter composed of a CR circuit is used as the differentiating circuit 14, and its cutoff frequency is set to about 10 times the maximum fundamental frequency (for example, about 37 MH _{Z in the} above example), and the information signal (b) The peak (bottom) position and the zero-cross point of the differential signal are made to substantially coincide with each other in time, and the zero-cross point is located approximately at the center of the gate signal (e) by the level slice so that the nozzle N is removed.

[0007]

When an attempt is made to improve the transfer rate from an optical disk, the number of revolutions of the optical disk is generally increased, but the maximum fundamental frequency of the reproduction signal from the optical disk is correspondingly high. Becomes
For example, when rotating the optical disc having a diameter of 130mm at 3600rpm or 5400 rpm, the maximum fundamental frequency of the ISO standard will be 7.4MH _Z or 11.1MH _Z.

When improving the transfer rate in this way,
If the cutoff frequency of the differentiating circuit in the conventional circuit remains the same, the peak (bottom) position of the reproduction signal and the zero-cross point of the differentiating signal are generated due to the phase characteristics of the CR circuit that constitutes the differentiating circuit as shown in FIG. A temporal phase shift τ occurs. As a result, when the level of the information signal (b) obtained from the photoelectric converter 13 fluctuates and the pulse width of the gate signal (e) becomes narrower, the data pulse (d) corresponding to the zero cross point of the differential signal (c) is changed. The rising position is deviated from the gate signal, and as can be seen from the waveform of the output signal (g) of the AND circuit, the data signal indicated by the arrow is lost, and the information (a) on the information recording medium 1 is accurately recorded. Reproduction becomes impossible.

[0009] Therefore, in the conventional circuit in response to the increase of the maximum fundamental frequency, the cut-off frequency, for example, 3600rpm of the differentiation circuit 14, respectively 74MH _Z in accordance with the rotational speed of 5400 rpm, to be raised with 111MH _Z Of course, if the cutoff frequency of the differentiating circuit is increased, the influence of noise mixed in the reproduced signal will increase accordingly, and the S / N ratio of the differentiating signal will be significantly deteriorated as shown by (c1) in FIG. There was a problem that it would end up.

In view of the above-mentioned problems, the present invention, in the case where the number of rotations of the optical information recording medium is increased to improve the transfer rate, even if the maximum fundamental frequency of the reproduced signal is relatively high, The cutoff frequency of the differentiating circuit for differentiating the reproduced signal is suppressed so that the S / N ratio is not deteriorated, and erroneous information is prevented from being reproduced by the spring noise N generated in the zero-cross detection signal. It is an object of the present invention to obtain a reproduction signal processing circuit capable of reproducing information.

[0011]

In order to achieve the above-mentioned object, a reproduction signal processing circuit according to the present invention receives a reproduction beam from an optical information recording medium irradiated with a laser beam. And a photoelectric detecting means for outputting an electric signal according to the optical information in the reproduction beam, a differentiating means for differentiating the electric signal from the photoelectric detecting means, and a zero-cross detection for zero-cross detecting the output signal from the differentiating means. Means, and a gate signal creating means for creating a gate signal by level slicing the electric signal from the photoelectric detection means,
Delay means for delaying the gate signal by a predetermined time; and gate circuit means for outputting an information output signal by gating the output signal from the zero-cross detecting means with the gate signal delayed by the delay means. It is characterized by having.

According to a second aspect of the present invention, there is provided a reproduction signal processing circuit according to the first aspect, wherein the differentiating means has the maximum fundamental frequency of 2 to 2 of the maximum fundamental frequency of the reproduction signal obtained from the reproduction beam. It is characterized by having a cutoff frequency in the range of four times.

[0013]

In the reproduction signal processing circuit of the present invention, the photoelectric detection means receives a reproduction beam from the optical information recording medium irradiated with the laser beam and outputs an electric signal corresponding to the optical information in the reproduction beam. Output. The electric signal from the photoelectric detecting means is differentiated by the differentiating means, and the output signal from the differentiating means is zero-cross detected by the zero-cross detecting means. On the other hand, the gate signal creating means creates a gate signal by level slicing based on the electric signal from the photoelectric detecting means, and the gate signal is delayed by the delay means for a predetermined time. The gate circuit means outputs an information output signal by gating the output signal from the zero-cross detection means with the gate signal delayed by the delay means, and a source generated in the output signal from the zero-cross detection means. Noise is removed to prevent erroneous reproduction of information.

The cutoff frequency of the differentiating means is preferably set within a range of 2 to 4 times the maximum fundamental frequency of the reproduction signal obtained from the reproduction beam. This is the conventional case
Since the cutoff frequency is 1/2 or less, the S / N ratio of the output signal from the differentiating means is reduced less than in the conventional example.

For example, as shown in FIG. 6, when the cutoff frequency f _c of the differentiating circuit is set to twice the maximum fundamental frequency f _max , the phase shift amount for the ideal differentiating circuit in the differentiating circuit is 90 °. -63.4 ° = 26.6 °
Next, (when the rotation speed is 3600rpm in ISO standard, the maximum fundamental frequency is 7.4MH _Z) rotating an optical disk having a diameter of 130mm at 3600rpm when was the peak (bottom) position of the information signal (b) And the time shift amount τ between the zero cross point of the differential signal (c) is 9.98.
It is about nsec.

The delay of the gate signal by the delay means may be set corresponding to the above-mentioned time shift amount τ, whereby the zero cross point of the differential signal can be set to the substantially central position of the gate signal, and the zero cross detection signal Noise can be effectively removed, and the loss of the data signal can be prevented.

[0017]

FIG. 1 is a block diagram showing an embodiment of a reproduction signal processing circuit according to the present invention. In FIG. 1, 1 is an information recording medium such as an optical disk, 2 is a photodetector composed of an optical element for capturing a reproduction beam, 3 is a photoelectric converter for receiving the reproduction beam, and its electric signal output is a differential circuit composed of a CR circuit. Differentiated by the circuit (HPF) 4, the differentiated output becomes a pulse signal by the comparator processing by the zero-cross detection circuit 5. The gate signal generation circuit 6 level-slices the electric signal from the photoelectric converter 3 to generate a gate pulse,
The gate pulse is delayed by the delay circuit 8 and input to the AND circuit 7. The AND circuit 7 gate-processes the pulse signal from the zero-cross detection circuit 5 with this delayed gate pulse to take out reproduction output information.

Information (A) such as prepit information and mark information is recorded on the information recording medium 1 as shown in FIG. 2, and a reproduction beam of this information (A) is recorded on the photodetector 2.
When incident on the photoelectric converter 3 via the, the information signal (B) as an electric signal is taken out from the photoelectric converter 3.

The information signal (B) is differentiated by the differentiating circuit (high-pass filter) 4 composed of a CR circuit or the like to become a differential signal (C), and this differentiating circuit (C) is processed by the comparator in the zero cross detection circuit 5. Then, the zero-cross signal (D) as a pulse signal is output.

The information signal (B) obtained from the photoelectric converter 3 is also sent to the gate signal producing circuit 6 and sliced at a preset DC level to produce a gate pulse (E).

Here, the cut-off frequency of the differentiating circuit 4 is set to 2 to 4 times the maximum fundamental frequency. Therefore, as shown in FIG. 2, the peak (bottom) of the information signal (B). There is a temporal phase difference τ between the position and the zero cross point of the differential signal (C). Therefore, in this embodiment, the gate signal (E) output from the gate signal generating circuit 6 is output.
Is delayed by the time τ by the delay circuit 8 so that the pulse rising position on the zero-cross point obtained by the zero-cross detection circuit 5 and the center of the gate pulse (F) obtained by the gate signal generation circuit 6 and the delay circuit 8 substantially coincide with each other. Then, the AND circuit 7 outputs only the reproduction signal (G) corresponding to the information (A) such as the pre-pit information and the mark information.
To take out from.

In the case of the recording format by the pit position system using the (2,7) code modulation, it is calculated that the delay time τ takes a substantially constant value regardless of the reproduced frequency. It has been confirmed in experiments,
Therefore, it is clear that the present invention correctly reproduces the information on the disc medium.

[0023]

As described above, according to the present invention, when the number of rotations of the optical information recording medium is increased to improve the transfer rate, the maximum fundamental frequency of the reproduced signal is relatively high. , It is possible to suppress the cutoff frequency of the differentiating circuit for differentiating the reproduced signal to prevent the deterioration of the S / N ratio, and to prevent the reproduction of erroneous information due to the noise generated in the zero-cross signal. There is an effect that the information on the information recording medium can be accurately reproduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a reproduction signal processing circuit showing an embodiment of the present invention.

FIG. 2 is a diagram showing an output waveform of each part of the reproduction signal processing circuit in FIG.

FIG. 3 is a block diagram of a conventional reproduction signal processing circuit.

FIG. 4 is a diagram showing an output waveform of each part of the reproduction signal processing circuit in FIG.

5 is a diagram showing an output waveform of each part of the reproduction signal processing circuit when the cutoff frequency of the differentiating circuit in the reproduction signal processing circuit in FIG. 3 is lowered.

FIG. 6 is a diagram showing general frequency characteristics and phase characteristics of a differentiating circuit.

[Explanation of symbols]

 1: Information recording medium 2: Photodetector 3: Photoelectric converter 4: Differentiation circuit 5: Zero-cross detection circuit 6: Gate signal creation circuit 7: AND circuit 8: Delay circuit

Claims (2)

[Claims] 1. A photoelectric detection means for receiving a reproduction beam from an optical information recording medium irradiated with a laser beam and outputting an electric signal according to optical information in the reproduction beam; Differentiating means for differentiating the electric signal, zero-cross detecting means for detecting the zero-cross output signal from the differentiating means, gate signal creating means for creating a gate signal by level slicing the electric signal from the photoelectric detecting means, and Delay means for delaying the gate signal by a predetermined time, and gate circuit means for outputting an information output signal by gating the output signal from the zero-cross detection means with the gate signal delayed by the delay means. A reproduced signal processing circuit characterized by being provided. 2. The reproduction signal processing circuit according to claim 1, wherein the differentiating means has a cutoff frequency within a range of 2 to 4 times the maximum fundamental frequency of the reproduction signal obtained from the reproduction beam. .