JPH0215475A - On-track detecting circuit - Google Patents

Abstract

PURPOSE:To prevent the erroneous detection of an on-track by holding a mean level before a velocity lowering detected signal is generated in response to the velocity lowering detected signal of a relative velocity in a direction orthogonal to the recording track of a pickup and comparing the held mean level with the output signal of the pickup. CONSTITUTION:Return light from a pickup 1 is detected in a return light quantity detecting circuit 2 and supplied to a comparing circuit 4. While the output of the return light quantity detecting circuit 2 is supplied to a comparator 5, the output is supplied to a mean level detecting circuit 6. The output of the mean level detecting circuit 6 is impressed through an analog switch 7 to a holding capacitor C2, and when the switch 7 is turned off, the output of the mean level detecting circuit 6 immediately before the switch 7 is turned off is held in the capacitor C2. A tracking error signal 10 is supplied to a velocity lowering detecting circuit 9, and the switch 7 is turned off by the detected signal. Further, the output of the mean level detecting circuit 6 held in the capacitor C2 is compared with the output of the return light quantity detecting circuit 2 in the comparator 5, and the on-track is detected.

Description

TECHNICAL FIELD The present invention relates to an on-track detection circuit that detects the presence of an information reading point of a pickup on a recording track in a disk recording/reproducing apparatus.

Background Art When recording information on a recording disk or reading recorded information, in order to move the pickup at high speed in a direction perpendicular to the recording track in order to search for the recording position, it is necessary to increase the relative speed of the pickup in the direction perpendicular to the track. A speed control servo device is essential that detects the relative speed and drives the pickup according to the detected relative speed to control the relative speed of the pickup in the direction orthogonal to the track. When the pickup is driven by this speed control servo device, the tracking servo loop that finely adjusts the relative position of the pickup's information reading point in the direction orthogonal to the track is turned on, and the brake is activated when the pickup's information reading point reaches the target track. control is performed so that the tracking servo loop is closed. At this time, the third
An on-track detection signal outputted from an on-track detection circuit as shown in the figure and indicating the presence of an information reading point of the pickup on the recording track is used as a timing signal for applying the brake.

In FIG. 3, the pickup 1 has a line connecting the centers of three beams, consisting of a main beam for information detection and two sub-beams for tracking error detection placed on both sides of the main beam, at a predetermined position with respect to the track. The three beams are irradiated onto the recording surface of a disk (not shown) at an offset angle of ing. The outputs of the two light-receiving elements for tracking error detection output from the pickup 1 are supplied to an error signal generation circuit (not shown) that generates a tracking error signal by a well-known method called the three-beam method. It is also supplied to the return light amount detection circuit 2. The return light amount detection circuit 2 is composed of an addition circuit that adds the outputs of two light receiving elements for tracking error detection, for example. A return light amount detection signal is generated according to the amount of the returned light.

Return light: The output of the detection circuit 2 is supplied to the comparison circuit 4. In the comparator circuit 4, the output of the return light amount detection circuit 2 is supplied to a zero cross comparator 3 via a DC cut capacitor C1. A bias resistor R is connected between the input terminal of the zero-cross comparator 3 and ground. The zero cross comparator 3 is configured to compare the input signal with a ground level and output a signal according to the comparison result. The output of this zero cross comparator 3 is supplied to a speed control servo device, etc. as an on-track detection signal.

In the above configuration, when the information reading point of the pickup is moved in a direction perpendicular to the recording track by the speed control servo device, the amount of reflected light on the recording track decreases, so the level of the return light amount signal is, for example, It is low when the information reading point is on the recording track, and high when the information reading point of the pickup is not on the recording track. Therefore, the returned light amount signal becomes a signal having a frequency corresponding to the relative speed of the pickup in the direction perpendicular to the track.

Therefore, when the relative speed of the pickup in the direction perpendicular to the track gradually decreases, the waveform of the return light amount signal becomes as shown by the solid line in FIG. 4(A).

The DC component of this returned light amount signal is removed by the capacitor C1, and the changing average level is made equal to the ground level as shown by the broken line in FIG. 4(A), and the signal is supplied to the zero cross comparator 3. . When the track crossing frequency corresponding to the relative speed of the pickup in the direction perpendicular to the track is sufficiently higher than the cutoff frequency fc determined by the capacitor CI and the resistor R, this average level is equal to the level when the information reading point is on the track. When the relative velocity of the pickup in the direction perpendicular to the track, that is, the track-crossing frequency becomes less than or equal to the cutoff frequency fC (after time t1), the intermediate level The level deviates from that. Therefore, until time t1, when the information reading point of the pickup is on the recording track, it is below the input cover ground level of the zero cross comparator 3, and when the information reading point is not on the recording track, the zero cross comparator 3 The input level will be higher than the ground level.

However, after time t1, even when the information detection point of the pickup does not exist on the recording track, the input of the zero-cross comparator 3 may be below the ground level.

Therefore, in the conventional on-track detection circuit, when the track-crossing frequency corresponding to the relative speed of the pickup in the direction orthogonal to the track is sufficiently higher than the cutoff frequency fc, as shown in FIG. The detection signal is outputted from the zero cross comparator 3 without error, but when the track crossing frequency corresponding to the relative speed of the pickup in the direction perpendicular to the track becomes less than the cutoff frequency fC, an incorrect on-drag detection signal e is outputted. There was a problem.

Summary of the Invention The present invention has been made in view of the above points, and includes:
An object of the present invention is to provide an on-track detection circuit that can prevent false detection.

In order to achieve the above object, the on-track detection circuit according to the present invention provides a speed reduction detection circuit that generates a speed reduction detection signal when the relative speed of the information reading point of the pickup in the direction orthogonal to the recording track becomes less than or equal to a predetermined value. means for generating an on-track detection signal by comparing the output signal of the pickup with an average level thereof; and a comparison means for generating an on-track detection signal by comparing the output signal of the pickup with an average level thereof; This is configured to be compared with the output signal of the pickup.

EXAMPLES Hereinafter, examples of the present invention will be described in detail with reference to FIGS. 1 and 2.

In FIG. 1, a pickup 1, a return light amount detection circuit 2
and comparison circuit 4 are connected in the same way as the circuit of FIG. However, in the comparison circuit 4 in this example, the output of the return light amount detection circuit 2 is supplied to the comparator 5, and also to the average level detection circuit 6, which includes an integrating circuit or the like. The output of the average level detection circuit 6 is applied to a hold capacitor C2 via an analog switch 7. A holding means is formed by the analog switch 7 and the capacitor C2, and when the analog switch 7 is turned off, the output of the average level detection circuit 6 immediately before it is turned off is held in the capacitor C2.

The output of the average level detection circuit 6 held in the capacitor C2 is supplied to the comparator 5 and returns to the light amount detection circuit 2.
is compared with the output of The output of this comparator 5 is output as an on-track detection signal.

A control input terminal of the analog switch 7 is supplied with a speed decrease detection signal output from a speed decrease detection circuit 9. The analog switch 7 is configured to be turned off by this speed reduction detection signal. The speed reduction detection circuit 9 is supplied with a tracking error signal generated by a tracking error signal generation circuit 10. The tracking error signal generation circuit 10 is configured to generate a tracking error signal based on the difference in the outputs of two light receiving elements for detecting a tracking error from the pickup 1 using, for example, a push-pull method.

In the speed reduction detection circuit 9, the tracking error signal is supplied to a zero cross comparator 11. The zero cross comparator 11 is configured to compare an input signal with a ground level and output a signal according to the comparison result.

The output of this zero cross comparator 11 is supplied to a speed detection circuit 12. The speed detection circuit 12 is configured to output, for example, a signal corresponding to the frequency of the output pulse of the zero-cross comparator 11 as a speed detection signal.

The output of this speed detection circuit 12 is supplied to a comparator 13 and compared with a reference voltage Vr.

The output of the comparator 13 is supplied to the control input terminal of the analog switch 7 as a speed reduction detection signal.

The operation of each part in the above configuration will be explained with reference to FIG. 2. Similar to the circuit of FIG. 3, when the relative speed of the information reading point of the pickup 1 in the direction perpendicular to the track gradually decreases, the returned light amount signal becomes as shown by the solid line in FIG. 2(B). Further, in the average level detection circuit 6, the returned light amount signal is integrated, for example, to form a signal as shown by the broken line in FIG. 2(B) corresponding to the average level of the returned light amount signal. The level of the output of the average level detection circuit 6 is such that the information reading point is determined when the track crossing frequency corresponding to the relative speed of the pickup in the direction perpendicular to the track is sufficiently higher than the cutoff frequency fC of the integrating circuit in the average level detection circuit 6. The level corresponds to the intermediate level between the level when the pickup is on the track and the level when it is between the tracks, and the track crossing frequency according to the relative speed of the pickup in the direction perpendicular to the track is lower than the cutoff frequency fc. When (after time t2),
The level is shifted from the intermediate level.

Therefore, until time t2, when the information reading point of the pickup exists on the recording track, the level of the return light amount signal is below the level of the output of the average level detection circuit 6, and the information reading point does not exist on the recording track. At this time, the level of the returned light amount signal is higher than the level of the output of the average level detection circuit 6. However, after time t2, even when the information detection point of the pickup does not exist on the recording track, the level of the return light amount signal may be lower than the level of the output of the average level detection circuit 6.

On the other hand, in the tracking error signal generation circuit 10, as shown in FIG. 2(A), a tracking error signal having a frequency corresponding to the relative speed of the information reading point of the pickup in the direction orthogonal to the track is generated, similar to the return light amount signal. . Since this tracking error signal is supplied to the zero-cross comparator 11, the zero-cross comparator 11 outputs a pulse having a pulse width corresponding to the relative speed of the information reading point of the pickup in the direction orthogonal to the track. Since the output pulse of the zero cross comparator 11 is supplied to the speed detection circuit 12, a speed detection signal having a level corresponding to the relative speed of the information reading point of the pickup in the direction orthogonal to the track is generated. Here, if the reference voltage Vr of the comparator 13 to which this speed detection signal is supplied is set to a value corresponding to the cutoff frequency fC of the integrating circuit in the average level detection circuit 6, the relative When the track crossing frequency corresponding to the speed becomes equal to the cutoff frequency fC, the comparator 13 outputs a speed reduction detection signal and the analog switch 7 is turned off. Then, the output of the average level detection circuit 6 immediately before turning off is held in the capacitor C2 and supplied to the comparator 5.

Therefore, the level of the signal compared with the returned light amount signal in the comparator 5 is always higher than the level of the returned light amount signal when the information reading point of the pickup is on the recording track; When not in use, the level is always lower than the level of the return light amount signal. As a result, a low-level on-track detection signal is outputted from the comparator 5 without error as shown in FIG. 2(C).

In the above embodiment, the tracking error signal is
Although the tracking error signal is generated by the push-pull method, speed reduction can also be detected by a signal generated by the so-called sampled servo method described in Japanese Patent Application No. 63-93882. Further, in place of the tracking error signal, speed reduction can also be detected using a 16-track count pulse that is formed to be inverted every time the information reading point of the pickup moves by 16 tracks in a so-called sampled servo system.

Effects of the Invention As detailed above, in the on-track detection circuit according to the present invention, when the relative speed of the information reading point of the pickup in the direction orthogonal to the recording track becomes less than a predetermined value, a speed reduction detection signal is generated. A detecting means is provided, and the comparing means generates an on-track detection signal by comparing the output signal of the pickup with its average level.The comparing means responds to the speed reduction detection signal and maintains the average level immediately before the generation of the speed reduction detection signal. Since the configuration is such that the output signal of the pickup is compared with the output signal of the pickup, the average level of the signal obtained from the recording disk decreases as the relative speed of the information reading point of the pickup in the direction orthogonal to the recording track decreases. Even if the signal obtained from the recording disk deviates from the intermediate level between the on-track level and the off-track level, the average level immediately before the relative speed fell below a predetermined value is maintained and comparison is possible. This makes it possible to prevent false detection.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of each part of the device shown in FIG. 1, and FIG. 3 is a block diagram showing a conventional on-track detection circuit. , 4th
The figure is a waveform diagram showing the action of each part in FIG. 3. Explanation of symbols of main parts 5... Comparator 6... Average level detection circuit 7... Analog switch 9... Speed reduction detection circuit 9 C2... capacitor

Claims (1)

[Claims] On-track detection comprising comparison means for generating an on-track detection signal indicating the presence of an information reading point of the pickup on a recording track formed on a recording surface of a recording disk by comparing an output signal of the pickup with its average level. The circuit includes speed reduction detection means for generating a speed reduction detection signal when the relative speed of the information reading point of the pickup in a direction perpendicular to the recording track becomes equal to or less than a predetermined value, and the comparison means is configured to detect the speed An on-track detection circuit characterized in that, in response to a reduction detection signal, an average level immediately before the generation of the speed reduction detection signal is held and this is compared with the output signal.