JPS62141643A - Focusing error detecting circuit - Google Patents

Abstract

PURPOSE:To stabilize focusing servo and stabilize recording at the head of a sector by inserting summing amplifiers in the input side and output side of an AGC circuit respectively, and adding specified voltage to each of them. CONSTITUTION:A summing amplifier 6 adds specified voltage V1 to a focus error signal 9, and the output 12 is inputted to an AGC circuit 7. A summing amplifier 8 adds specified voltage V2 to the output signal 11 of the AGC circuit 7 and a focus error signal 13 made by correcting the output by AGC control and summing amplifiers 6, 8 is obtained. The 0V point of the output signal 11 of the AGC circuit 7 does not always coincide with the focus point due to added voltage V1 added by the summing amplifier 6. Therefore, additional voltage V2 is added by the summing amplifier 8 to cancel additional voltage V1 to make 0V of the output signal 11 of the AGC circuit at the time of recording coincide with the focus point. Thus, 0V of the focus error signal 13 indicates the focus point at the time of recording, and shifting of focus point does not occur even when reproducing and recording operations are repeated alternately, and stable focus error signals can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is applicable to an original disk device in which the emitted light is focused on the medium by adjusting the distance variation between the light source and the medium. The present invention relates to a focus error detection circuit for detecting a servo error detection signal for adjusting the lens position using light, and more specifically, to an improvement in the operating point of an AGC circuit used in the circuit.

(Prior Art) The AGC circuit used in the focus error detection circuit described above has the function of controlling the circuit gain so that the output signal amplitude remains constant despite fluctuations in the input signal amplitude. .

When obtaining an erroneous servo M signal from light reflected from the medium in the original disk device, the output photoelectric power of the head changes from 1 to 10 times during playback and recording, and the medium reflectance changes. In order to prevent the servo gain from fluctuating due to changes in the servo error signal amplitude, the AGC circuit described above is inserted to obtain a constant signal sensitivity range.

FIG. 3 is a diagram showing an example of a focus error detection circuit in a conventional original disk device. Below, we will explain the operation of this figure and address the problems.

In FIG. 3, the source incident on the two-split photodetector 1 is the source −
After voltage conversion, the two outputs of the two-split photodetector 1 are input to a differential amplifier 4 and a separate amplifier 5 via preamplifier circuits 2 and 3, respectively.

Here, the differential amplifier 4 outputs a focus error signal (servo error signal), and the output of the addition multiplier 5 is inputted to the AGC circuit 7 as a control atl signal 10.

Since the AGC circuit 7 is configured to change the control signal 10 by an increment of 14 in inverse proportion to the control signal 10, the two-split photodetector 1
If the incident xi is doubled, the amplification factor of 800 becomes 17z
become. Therefore, even if the focus error signal 9 fluctuates, the fluctuation is suppressed by the AGC circuit 7, and as a result, the focus error signal output from the AGC circuit 7 is maintained at the value of the cutting of the incident light f.

Next, the characteristics of the focus error signal during reproduction and recording will be explained.

4 is a diagram showing the relationship between the lens movement position and the focus error signal 9 during reproduction and recording, and FIG. 5 is a diagram showing the relationship between the output power of the optical head and the amount of focus movement.

The optical head of the original disk device uses a semiconductor laser 7 as a light source.
The output power of the optical head is 1mW during playback.
It is used before and after tomw during recording. Here, as the amount of emitted FE from the original head increases, the characteristics of the focus error signal change from the characteristics of a reproduction puff to those of the recording power W due to the movement of the light emitting point of the semiconductor. Each of these characteristics in this figure shows that as the amplitude of the focus error signal increases, the lens movement position to be adjusted also increases.

As is clear from Figure 5, the relationship between the output power and the amount of movement is that the amount of movement increases depending on the output power. Figure 6 shows the AGC circuit output characteristics when a focus error signal with the characteristics shown in Figure 4 is input. FIG. 2 is a diagram showing the relationship between the AGC circuit output signal imaging width and the lens movement position.

When the reproduction and recording operations shown in characteristic 7 of the focus error signal 9 are repeated, the AGC circuit output 11ilC 6th
As shown in the figure, the characteristics a during playback and the characteristics W during recording
This means that there will not be a single piece.

Therefore, if the playback and recording operations are repeated 7 times with the focus servo on, the lens position will move from point O to point A during playback → recording, and conversely move from point A to point 0 during recording → playback. In addition to unstable operation, the spot position at the start of recording is not necessarily at the sharp focus, resulting in phenomena such as insufficient signal quality at the head of the sector.

(While the invention is trying to solve this problem!) In the above-described conventional AGC circuit operation, there is no problem in use as long as there is only a change in the amount of incident light.
When the focusing position moves when the amount increases, the focus error signal of the AGC circuit output does not disperse during playback and recording, so repeating playback and recording operations will dig the lens and make the focusing servo unstable. There is a drawback that recording at the head of a sector becomes unstable as the number increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks, and to provide a focus error detection circuit that can stabilize the focusing servo χ regardless of reproduction or recording, and can also stabilize recording at the head of a sector. .

(Means for Solving the Problems) In order to achieve the above object, the focus error detection circuit according to the present invention focuses the emitted light on the medium in response to distance fluctuations between the light source and the medium. In the focus error detection circuit that detects the servo error No. 11 for adjusting the lens position and V in the reflected light, there is a two-split photodetector that detects the reflected light, and a first one that adds the two outputs of the two-split photodetector. 7111 arithmetic amplifier, and two of the two-split photodetector.
a differential amplifier that amplifies two outputs; a second summing amplifier that adds the output of the differential amplifier to a first predetermined voltage; and a second summing amplifier that adds the output of the second 7JEI amplifier to the output of the first summing amplifier. and a third summing amplifier that adds a second predetermined voltage ya1' to the output of the AGC circuit, and the first predetermined voltage is set when the input operating point of the AGC circuit is the original power of the light source. The second predetermined voltage is set to a value that is a cross point between the output of the second summing amplifier during output and the output of recording power, and the second predetermined voltage is set to a value that cancels out the first predetermined voltage value. It is composed of

(Example) Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a second embodiment of a focus error detection circuit according to the present invention. In the figure, a two-split photodetector 1
The reflected light from the medium that is incident on the medium is subjected to light-to-voltage conversion.

The two outputs of the two-split photodetector 1 are respectively connected to the preamplifier 2.
．． 3 to a differential amplifier 4 and a summing amplifier 5. The difference between the two signals from the preamplifier 2.3 is input to the differential amplifier 4, and its output becomes the focus error signal 9. In addition, the summing amplifier 5 is supplied with 2 from the preamplifier 2.3.
The output of the two signals becomes the gain control voltage 10 of the AGC circuit 7.

The focus error signal 9 has the same characteristics as shown in FIG. The summing amplifier 6 adds a predetermined voltage VtY to the focus error signal 9, and its output 12 is input to the AGC circuit 7. Figure 2 (bl shows the output characteristic 2 of the addition amplifier 1 @ unit 6. In the AGC circuit, the gain is controlled to be inversely proportional to the control voltage 10, so the amplitude fluctuation of the input signal of the AGC circuit 7 However, the output signal 11 has a constant amplitude.

A summing amplifier 8 adds a predetermined voltage V2Y to the output signal 11 of the AGC circuit 7, and a focus error signal 13 is obtained after the output is subjected to AGC control and correction by an arithmetic amplifier 6.8. Figure 2(b) shows the focus error signal 1.
Characteristic 2 of 3 is shown.

Next, with reference to Figure 2, add voltages Vl, Vz (first
A method of determining the second predetermined voltage] will be described.

FIG. 2(a) shows the signal amplitude on the vertical axis and the lens movement position on the horizontal axis, where the R characteristic shows the focus error signal at one time of the reproduction power, and the W characteristic shows the focus error signal at one time of the recording power. 0
The point is the oV point of the input signal 11 of the AGC circuit 7 when the blade calculation voltage Vl = oV (the input operating point of the conventional circuit). If adopted, it will match the characteristics shown in FIG.

Therefore, when Vs = o V, the output signal 11 of the AGC circuit 7 becomes as shown in FIG. 6, and the characteristics at the time of reproduction and recording do not match, resulting in a positional shift of the focal point.

Next, the Otori P where the ordinary characteristics and the characteristics of W intersect is 〇〇Circuit 7
It is assumed that the 7JIl calculated voltage Vl is set to a value such that the input signal Ov becomes 0 (input operating point in the present invention).

The output signal 11 of the AGC circuit 7 in the case of
In this way, the ordinary characteristics and the characteristics of W overlap.

This means that the output signal 11 does not change even after switching between reproduction and recording, and no movement of the lens occurs.

Next, since the output signal 11 of the AGC circuit 7 is due to the overload pressure Vx obtained by the output amplifier 6, its oV point does not necessarily coincide with the in-focus point.

Therefore, in order to cancel the added voltage Vty by the 7111 calculation amplifier 8, the 71Q calculation voltage Vzyl is added, and the OV of the output signal 11 of the AGC circuit during recording is brought into focus.

As a result, the focus error signal 13 becomes 0 ■ In-focus point when recording Chikaraina? Even if the playback and recording operations are repeated, no movement of the focal point will occur.
A stable focus error signal can be obtained.

(Effects of the Invention) As described above in detail, the focus error detection circuit according to the present invention is applied to the input side and output side of the AGC circuit that performs one-time control to obtain a constant focus error signal with respect to fluctuations in incident light ′+i. A summing amplifier is inserted in each case, and the input side summing amplifier applies a 710 χ calculation to the input signal of the AGC circuit.
Then, the input operating point of the AGC circuit is selected to be the intersection point of the focus error signal when the original head outputs the reproduction power and the recording power, and the input is added to the output side by /x, and the input to the AGC circuit output is Since the configuration is such that the voltage V2χ is added to cancel the voltage Vt, there is no shift in the focal point of the focus error signal due to an increase in the output power of the original head, and the lens position does not move even if playback and recording are repeated alternately. This enables stable focusing servo. As a result, there is also the effect that the recording quality at the beginning of the sector is improved.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the focus error detection circuit according to the present invention, and Fig. 2 is an explanatory diagram of the operation in this embodiment. b) shows the characteristics of the eight outputs of the 710 arithmetic amplifier. Fig. 3 shows the conventional focus error signal production circuit.
FIG. 4 is a characteristic diagram of a focus error signal which is an input signal to an AGC circuit in a conventional example, and shows the reproduction power at one time and the recording power at one time. FIG. 5 is a characteristic diagram showing the relationship between the amount of light emitted from the original head and the amount of focus movement, and FIG. 6 is a characteristic diagram of the focus error signal which is the output of the AGC circuit in a conventional example. 1... 2-split photodetector 2.3... Preamplifier 4
...Differential amplifier 5, 6.8...710 Step-up amplifier 7...AGC circuit 9...Focus error signal 1
0...Control signal (control voltage) 11...AGC circuit output signal 12...AGC circuit input signal Patent applicant NEC Corporation Representative Patent attorney Inoro Libel 1 Figure 22 (a) ) (b) Sai 31i (I ``26 fig.

Claims (1)

[Claims] In order to focus the emitted light on the medium when the distance between the light source and the medium changes, the reflected light is detected in a focus error detection circuit that detects a servo error signal for adjusting the lens position using the reflected light from the medium. a two-split photodetector for detection, a first summing amplifier that adds two outputs of the two-split photodetector, a differential amplifier that amplifies the difference between the two outputs of the two-split photodetector, and the difference a second summing amplifier that adds the dynamic amplifier output and a first predetermined voltage; and an AG that controls the second summing amplifier output by the first summing amplifier output.
C circuit, and a third summing amplifier that adds the AGC circuit output and a second predetermined voltage, and the first predetermined voltage records that the input operating point of the AGC circuit is when the optical power of the light source is output. The second predetermined voltage is set to a value that makes the output of the second summing amplifier intersect when the power is output, and the second predetermined voltage is set to a value that cancels the first predetermined voltage value. Features a focus error detection circuit.