JPH0619836B2 - Threshold level automatic control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write-once optical disc device, and more particularly, to a reproduction signal of a recorded portion, an additional recording portion and an unrecorded portion of a threshold level for binarizing a reproduction signal. The present invention relates to a threshold level automatic control circuit that can be optimally established according to the above.

[Background of the Invention]

In the write-once type optical disk device, there is no correlation in the signal properties between the reproduction signal of the already recorded portion recorded in advance as a phase groove on the disc and the reproduction signal of the write-once portion additionally recorded later, and their amplitude and binarization are performed. The appropriate threshold levels for doing so do not necessarily match.

The conventional device detects the average value of the input signal from each output of the circuit for detecting the maximum value and the minimum value of the input signal voltage as described in JP-A-56-115024, and there is no input signal. Even in such a case, a circuit for limiting the threshold level to a certain value or less is provided so that the threshold can be set in accordance with the amplitude variation and the DC level variation.

However, as described above, in the optical disk device, at least three signals having different properties are mixed.

That is, it is desirable that the recorded signal is accurately recorded as a phase groove, the amplitude fluctuation is small, and the envelope detection time constant is large.

On the other hand, the additional recording signal is recorded as a change in reflectance with a laser having a long wavelength, and has low recording accuracy and large amplitude fluctuation. Therefore, it is necessary to reduce the time constant and sufficiently follow the fluctuation of the amplitude.

In the unrecorded area, it is required that the peak due to noise is not detected with a sufficiently large time constant.

Further, even when the threshold value is set from the positive and negative envelopes of the signal, the average value of them is not the correct threshold value, or the voltage division ratio at which an appropriate threshold value is obtained for the recorded signal is the additional recording signal. However, there was a problem that the partial pressure ratio was not always correct.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned problems of the conventional device,
To provide a threshold level automatic control circuit capable of optimally setting a threshold level regardless of a recorded portion, an additionally recorded portion and an unrecorded portion even when two or more signals having different properties are mixed such as an optical disc. is there.

[Outline of Invention]

A feature of the present invention is that a flag signal indicating the additional recording area recorded at the head of the additional recording area is detected and
The additional recording portion and the non-recording portion are judged, and the detection time constants of the positive and negative envelope detection circuits and the ratio of dividing the threshold level from those envelopes are automatically switched to the signal areas having different properties. Set a proper threshold level according to, and than the maximum value of the envelope detection time constant of the positive envelope detection means,
The point is that the envelope detection time constant of the negative envelope detection means is increased.

Example of Invention

An embodiment of the present invention is shown in FIG. 1 and will be described below with reference to the drawings.

In the figure, 1 is an optical disc, 2 is a spindle motor for rotating the optical disc, 3 is an optical pickup for reproducing or recording a signal of the disc 1, and 4 is an optical pickup 3.
It is a pre-amplifier that amplifies the signal reproduced by. The reproduction signal amplified by the preamplifier 4 is supplied to the positive envelope detection circuit 5
Is input to the negative envelope detection circuit 6.

The positive envelope detection circuit 5 is composed of transistors 10, 11 resistors 12, variable resistors 14, resistors 15, capacitors 13 and switches 16. 28 and 29 are positive and negative power supplies, respectively. This positive envelope detection circuit 5 includes a resistor 12, a variable resistor 14 and a capacitor.
A first time constant of 13 and a second time constant of a resistor 12, the total resistance of the variable resistor 14 and the capacitor 13, and a resistor 12
And a third time constant consisting of capacitor 13. The time constant is selected to be an appropriate time constant by operating the switch 16 by the control circuit 9.

Negative envelope detection circuit 6 consists of transistors 17,18 resistors 19,20,2
1 and the capacitor 22. The negative envelope detection time constant is controlled by the control circuit 9 by switching the switch 23 to the resistor 20.
It is controlled to an appropriate time constant by turning on and off at the terminal.

The outputs of the positive and negative envelope detection circuits 5 and 6 are input to the threshold value switching circuit 7, which is an essential part of the present invention. The threshold switching circuit 7 is composed of variable resistors 24 and 25, a variable voltage section 26, and a switch 27.

The variable resistors 24 and 25 are used for the positive and negative envelope detection circuits 5 and 6, respectively.
The positive and negative envelopes detected in step 2 are divided at a constant ratio, and are adjusted in advance so that proper threshold values can be obtained for the recorded signal and the additionally recorded signal, respectively.
The variable voltage section 26 is provided to obtain a voltage higher than the negative envelope by a constant voltage, and the threshold value can be controlled even in the unrecorded section.

The control circuit 9 includes a flag detection circuit 30 and a second synchronization detection circuit.
31, a first synchronization detection circuit 32, a first counter 35, a second counter 34, and a switch control circuit.

FIG. 2 is a conceptual diagram of a reproduction signal. The already-recorded signals 37 and 46 which are pre-recorded as phase grooves on the disc are the first synchronization signal 41 for synchronizing with the clock and the address signal indicating the address. It is composed of 42,47. The signal 36 of the additional recording portion, which is recorded by the change in the reflectance on the disk surface, is the flag signal 43 indicating the additional recording portion recorded at the head thereof, and the second signal for synchronizing with the clock. It is composed of a synchronization signal 44 and data 45.

Gaps 38 and 39 in which no signals are recorded are provided between the recorded portions 37 and 46 and the additional recording portion 36.

FIG. 2 shows a state in which a signal has been additionally written at address n, but no signal has been additionally written at address n + 1.

Next, the operation of the above-described embodiment of the present invention will be described with reference to FIGS. FIG. 3 shows a waveform diagram of signals in the main part of FIG. 1, and the same reference numerals as those in FIG. 2 denote the same parts.

When the first synchronization detection circuit 32 detects the first synchronization signal 41 from the output signal of the voltage comparator 8, the flag detection circuit 30 is opened at a predetermined place where the flag signal 43 is written.
Also, the first counter 35 is reset.

The flag detection circuit 30, when the flag signal 43 is detected while the window is opened, to the switch control circuit 33,
A signal indicating that the additional recording unit is starting is sent. Upon receiving this signal, the switch control circuit 33 sets the switches 16 and 23 to the one with the smaller time constant, that is, connects the switch 16 to the terminal b of the variable resistor 14, turns on the switch 23, and switches the switch 27 to the additional write section. The appropriate voltage division ratio, for example, the variable resistor 25.

The write-once portion is a signal recorded as a reflectance change with a long wavelength laser, and has a low recording accuracy and a large amplitude fluctuation. The time constant is set to a value that can sufficiently follow this amplitude fluctuation.

When the second synchronization detection circuit 31 detects the second synchronization signal 44, the second counter 34 is reset by the output signal of the second synchronization detection circuit 31. The second counter 34
After recording the intermittent time of data 45, unrecorded gap
At 39, the switch control circuit 33 is sent a signal indicating that the additional recording section has ended. Upon receiving this signal, the switch control circuit 33 switches the switch 27 to an appropriate voltage division ratio for the recorded portion, for example, to the variable resistor 24, and the unrecorded gap 39.
In the section of, the positive envelope time constant is made smaller, that is, the switch 16 is switched to the terminal a. After that, when the unrecorded gap 39 ends, the switches 16 and 23 are switched so as to have a larger time constant, that is, the switch 16 is opened and the switch 23 is turned off.

The already-recorded signal is exactly recorded as a phase groove on the disc, and the fluctuation of the amplitude is small. Therefore, the positive envelope detection time constant is set to a larger value than in the case of the write-once portion. The negative envelope detection time constant is set to a value large enough to follow the gentle fluctuation of the unrecorded portion but not follow the spike noise.

Further, in the write-once medium, since the signal amplitude is generated by recording on the unrecorded part as a base, the reproduction signal is subject to amplitude modulation or the like depending on the recording condition and the level fluctuation is large. The optimum threshold level can be set by increasing the detection time constant of the negative envelope, which has a stable level fluctuation in the unrecorded portion and is desired to take only spike noise generated by loss of reflectance, rather than the value.

When the flag detection circuit 30 does not detect the flag signal 43 while the window is opened, it sends a signal indicating the unrecorded portion to the switch control circuit 33, and the switch receiving this signal The control circuit 33 switches the switch 27 to the variable voltage unit 26.
Switch to.

As described above, the first counter 35 reset by the output signal from the first synchronization detection circuit 32 sends a signal to the switch controller at the time when the next recorded signal starts.
The switch 27 is switched to a voltage division ratio suitable for the recorded signal.

In FIG. 3, the waveform shown in FIG. 3A is the output waveform of the preamplifier 4, and 48 and 49 are spike-like noises. E1 in Fig. 3 (b)
Indicates a positive envelope detected by the positive envelope detection circuit 5, and E2 in FIG. 3 (b) is a negative envelope detected by the negative envelope detection circuit 6. The positive and negative envelopes E1 and E2 are the additional recording section 36, the recorded sections 37 and 46, and the unrecorded section 38, as described above.
The detection time constant can be switched to an appropriate value according to the 39, 40 section, so the envelope curve detected with a single time constant is shown in Fig. 3 (b).
Compared to E1 'and E2' of, the correct envelope can be obtained.

FIG. 3 (c) shows the threshold T obtained from the positive and negative envelopes E1 and E2.
It shows h, and it is time A when the flag signal 43 is detected.
Thus, the threshold value appropriate for the recorded signal is switched to the appropriate threshold value for the additional recording signal. In addition, in the unrecorded gap portion B after the data 36 of the additional recording portion is finished, the switch 27 is changed again to the proper threshold value for the already recorded signal, and the switch 27 is changed at the time C when it is determined that it is not the additional recording area. By switching to the voltage unit 26, it is possible to always obtain the optimum threshold value.

FIG. 3 (d) is the binarization obtained by comparing the output signal (a) of the preamplifier 4 with the Th of the optimum threshold value (c) obtained as described above by the voltage comparator 8. It is a signal.

Therefore, according to the present embodiment, it is possible to binarize the input signal by detecting the envelope with an appropriate time constant and optimally setting the threshold value, regardless of the already recorded portion and the additionally recorded portion. This optimized threshold value does not follow spike-like noise in the unrecorded portion, and a threshold value obtained by level-shifting this threshold value can also be used to detect spike noise exceeding the constant amplitude in the unrecorded portion.

It should be noted that the above embodiments include positive and negative envelope detectors.
5 and 6 have two or more selectable time constant circuits, but this is not always necessary, one time constant circuit is fixedly provided, and variable resistors 24 and 25 are selected to appropriate values. You may do it.

Although one embodiment of the present invention has been described above, this is merely an example, and various modifications and changes can be made. For example, in this embodiment, the positive and negative envelopes of the signal are detected,
The threshold is set by taking the partial voltage, but instead, only the negative envelope is detected, and the same level is set when the threshold is set by adding a voltage of a certain level to this depending on the nature of the signal. The purpose can be achieved.

Further, in the present embodiment, the case where the reflectance increases as a result of recording, the signal level rises and the recorded signal level exceeds the recorded signal level in the unrecorded portion is described. Even if the level is not exceeded, or the reflectance is lowered due to recording and the level becomes smaller than that in the unrecorded portion, it is clear that the same effect as the first embodiment can be obtained.

According to the present invention, the detection time constants of the positive and negative envelope detection circuits and the ratio of dividing the threshold level from the envelopes are switched according to the input signal, and the positive envelope detection means. Since the envelope detection time constant of the negative envelope detection means is set to be larger than the maximum value of the envelope detection time constant of, even when signals having different characteristics are mixed, such as an optical disc,
The threshold level can be optimally set regardless of the recorded portion, the additionally recorded portion, and the unrecorded portion. Therefore, there is an effect that a correct binary signal can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a conceptual diagram of a reproduced signal, and FIG. 3 is a diagram showing signal waveforms of the circuit of the embodiment of FIG. 1 ... Disk 3 ... Optical pickup 4 ... Preamplifier 5 ... Positive envelope detection circuit 6 ... Negative envelope detection circuit 7 ... Threshold switching circuit 8 ... Voltage comparator 9 ... Control circuit

Claims (1)

[Claims] 1. In a write-once optical disc device, a signal side having two or more types of envelope detection time constants for detecting an envelope corresponding to a peak side of a reproduced signal of a recording section in a reproduced signal of an optical pickup output. Envelope detecting means, an unrecorded side envelope detecting means for detecting an envelope corresponding to a reproduced signal side of an unrecorded portion in the reproduced signal, and having two or more envelope detection time constants, the signal side Voltage dividing means for obtaining two or more kinds of divided voltage values at a predetermined ratio from the output signals of the envelope detecting means and the unrecorded side envelope detecting means, and the recorded portion, the additional recording portion, and the unrecorded portion of the reproduced signal. Determining means for identifying the recording portion; time constant switching means for switching the envelope detection time constants of the signal side envelope detecting means and the unrecorded side envelope detecting means by the output of the determining means; and the determining means. of Threshold value switching means for switching between two or more voltage division values of the voltage dividing means and a predetermined fixed voltage by force, and comparison means for comparing the output of the threshold value switching means with the reproduction signal and binarizing the reproduced signal. And a threshold level characterized in that the envelope detection time constant of the unrecorded side envelope detection means is made larger than the maximum value of the envelope detection time constant of the signal side envelope detection means. Automatic control circuit.