JPH0428021A - Signal characteristic measuring method for focusing error signal - Google Patents

Abstract

PURPOSE:To measure the degree of influence of the parting line of a photodetector by measuring a signal detection dead area relating to the parting line of the light receiving plane of the photodetector by the driving voltage of a signal waveform in which a first driving voltage is superimposed on a second driving voltage. CONSTITUTION:This first driving voltage A is applied from a first driving voltage source 15 to a driving amplifier 12. When the second driving voltage B from a second driving voltage source 16 is superimposed to the first driving voltage A from the first driving voltage source 15, an focusing error signal of sine waveform including a high frequency component can be obtained. The high amplitude of a frequency component in the neighborhood of a focal point can be reduced by performing signal detection by using the focusing signal including the high frequency component when the influence of the width of the parting line on the light receiving plane of the photodetector exists. Therefore, the degree of reduction of the amplitude can be measured. In such a way, the degree of influence of the parting line can be measured with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for measuring signal characteristics of a focus error signal.

2. Description of the Related Art Conventional methods for detecting focus error signals include, for example, the astigmatism method and the Knife-Fuji method. FIG. 8 shows the astigmatism method. That is, light emitted from a laser light source (not shown) passes through a polarizing beam splitter 1 and a λ/4 plate 2, is focused by an objective lens 3, is irradiated onto the surface of an optical disc 4, and is then reflected from the optical disc. The light is reflected by the polarizing beam splitter 1, condensed by the condenser lens 5, and received by the light receiving element 7 via the cylindrical lens 6, whereby a focus error signal can be detected. The light-receiving element 7 has light-receiving surfaces a, b, c, and d as shown in FIGS. 9(a), (b), and d.
○ can be determined by Fo= (a+c)-(b+d)-= (1). At this time, the beam 8 with astigmatism becomes a perfectly circular beam as shown in (b) when focused, and at near and far positions shifted from the focused point in the front and rear directions (a
) As shown in (C), the beam becomes a beam with astigmatism.

FIG. 10 shows a detection method using the knife method, in which the beam focused by the condenser lens 5 is partially cut off by the knife 9, and is irradiated onto the surface of the light receiving element 7. be done. The light receiving element 7
is the light receiving surface a as shown in FIGS. 11(a), (b), and (c).
, b, and the focus error signal FO can be obtained from Fo=a-b (2). In this case as well, when the beam is in focus, it becomes a perfect circular beam as shown in (b), and when it deviates from the focused point in the front-rear direction, it becomes a semicircular beam as shown in (a) and (c).

FIG. 6 shows an example of a focus drive circuit 1O that calculates the value of the focus error signal Fo as shown in equation (1) based on the amount of light received by the light receiving element 8. In this case, the focus error signal Fo is sent to the drive voltage source 11, and the drive voltage generated thereby (for example, a sine wave or side wave waveform) is transmitted through the drive amplifier 12.
When the signal is sent to the focus coil 13, its actuator section is driven to perform focus servo.

Further, FIG. 7 shows an example of a focus error signal detection circuit 14 that performs focus control based on the focus error signal Fo obtained in this manner.

Problems to be Solved by the Invention The focus servo performed by the method described above has a focus error signal FO whose element is the slope of the signal waveform as shown in FIG. 12 when setting the open loop gain. Therefore, if the slope of the focus error signal FO changes (the ratio of error voltage to distance fluctuations near the in-focus point), the stability of the focus loop deteriorates, making it impossible to perform highly accurate control. The dividing line 7a (see FIGS. 9 and 11) that divides the light-receiving surface of the light-receiving element 7 described above usually has a width of about several tens of μm to 100 μm. There is no (or very low) detection sensitivity in the area where the signal is detected (signal detection insensitive area).

If there is an influence of the dividing line 7a on signal detection in this way (
In particular, when the diameter of the received beam is set to be very small, the slope of the figure 8 characteristic of the signal waveform in Figure 12 becomes small near the focal point, making it impossible to obtain the desired gain. As a result, there is a problem that highly accurate focus servo cannot be performed.

Means for Solving the Problem Therefore, in order to solve such problems, claim 1
In the described invention, a predetermined signal is applied to a focus coil via a drive amplifier based on a focus error signal detected by a light receiving element having a plurality of divided light receiving surfaces of an optical pickup and output from a focus error signal detection circuit. A second drive voltage that is separate from the first drive voltage and has a higher frequency than the first drive voltage and that causes a very small displacement with respect to the amount of movement in the focus direction. The voltages are superimposed, and the signal detection insensitive area related to the dividing line of the light-receiving surface of the light-receiving element is measured from the drive voltage of the signal waveform in which the first drive voltage and the second drive voltage are superimposed.

In the invention according to claim 2, in the invention according to claim 1, the frequency of the second drive voltage superimposed on the first drive voltage is
It was set so that an amplitude of at least one period or more was generated with respect to the dividing line width of the light receiving surface of the light receiving element.

In the invention set forth in claim 3, in the invention set forth in claim 1, a filter circuit is connected to the output stage of the focus error signal detection circuit that outputs the focus error signal, and a filter circuit is connected to the output stage of the focus error signal detection circuit that outputs the focus error signal. The frequency was set so that an amplitude of at least one period or more was generated with respect to the dividing line width of the light-receiving surface of the light-receiving element.

In the invention according to claim 1, the normal first drive voltage (
By superimposing a separate second drive voltage that has a high frequency with respect to the sine wave or side wave waveform and causes a very small displacement with respect to the amount of movement in the focus direction, the focus error signal is different from that of the conventional focus error signal. It is possible to obtain a focus error signal with a fine local waveform that is different from the figure-8 characteristic of The degree of influence of the dividing line can be measured from the fact that the amplitude becomes smaller.

In the invention set forth in claim 2, in addition to the invention set forth in claim 1, the frequency of the second driving voltage is set such that an amplitude of at least one period or more is generated with respect to the dividing line width of the light receiving surface of the light receiving element. Therefore, amplitude fluctuations of the focus error signal near the in-focus point can be observed with high precision, thereby making it possible to more accurately detect the influence of the dividing line of the light receiving element.

In the invention set forth in claim 3, in addition to the invention set forth in claim 1 and the invention set forth in claim 2, a filter circuit is connected to the output stage of the focus error signal detection circuit. By passing the error signal, it becomes possible to measure amplitude fluctuations of the focus error signal near the in-focus point with higher precision.

Embodiment First, an embodiment of the invention as claimed in claim 1 will be explained based on FIGS. 1 to 3.

FIG. 1 shows the state of a focus drive circuit 10 for a focus error signal of an optical disc pickup. The drive amplifier 12 that excites the focus coil 13 of the optical pickup includes a first drive voltage source 15 (this is a sixth
(same as the drive voltage source 11 in the figure) is connected. This first drive voltage source 15 is a sinusoidal voltage source as shown in FIG. 2(a).
It functions to generate a wave or side wave first drive voltage A.

Further, the drive amplifier 12 includes the first drive voltage source 1
A second drive voltage source 16 is connected in parallel with 5. This second drive voltage source 16 has a higher frequency and is different from the first drive voltage source 15, and has a slight displacement with respect to the amount of focus movement, that is, as shown in FIG. 2(b). Nas
It has the function of generating an in-wave second drive voltage B.

A method for measuring the signal characteristics of the focus error signal in such a configuration will be described. Applying the -th drive voltage A from the first drive voltage source 15 to the drive amplifier 12,
By changing the position of an objective lens (not shown) driven via the focus coil 13, it is possible to obtain the figure-8 characteristic of the focus error signal Fo as shown in FIG.

At this time, when the second drive voltage B from the second drive voltage source 16 is superimposed on the first drive voltage A from the first drive voltage source 15, the si
A focus error signal FO of n waveforms can be obtained.

In this way, the focus error signal F containing high frequency components
By performing signal detection using O, if there is an influence of the width of the dividing line 7a (see Fig. 9) on the light receiving surface of the light receiving element 7, high frequency components will be detected near the focal point in the signal waveform of Fig. 3. A phenomenon appears in which the amplitude of . Therefore, by measuring the degree of decrease in the amplitude, it is possible to measure the degree of influence of the dead zone of the dividing line 7a with high precision.

Next, an embodiment of the invention according to claim 2 will be described. Here, in the focus drive circuit 10 for the focus error signal FO as shown in FIG. ) is set so that an amplitude of at least one period or more is generated with respect to the width of the dividing line 7a of the light-receiving surface of the light-receiving element 7.

By setting the focus error signal Fo in which the first drive voltage A and the second drive voltage B are superimposed in this way to have an amplitude of at least one period or more with respect to the width of the dividing line 7a, By observing the amplitude fluctuations of the signal waveform, it is possible to accurately measure the degree of influence of the dividing line.

Next, an embodiment of the invention according to claim 3 is shown in FIGS. 4 and 5.
This will be explained based on the diagram. Here, the focus drive circuit 1 as shown in FIG.
0, the focus error signal detection circuit 14 connected to the front stage of this measurement circuit has a special feature.

FIG. 4 shows the state of the focus error signal detection circuit. Here, a bandpass filter circuit 18 as a filter circuit is connected to the output stage of an amplifier circuit 17 connected to a light receiving element 7 having a light receiving surface divided into four parts. This bandpass filter circuit 18 receives a focus error signal F including a high frequency component as shown in FIG.

By passing the focus error signal Fo
The waveform of a, as shown in FIG.
Due to the influence of the width of , it becomes locally extremely close to O near the focal point. As a result, the focus error signal Fo
Since the amplitude fluctuation of a can be measured with higher accuracy, it becomes possible to measure the signal characteristics in the dead zone of the dividing line 7a more accurately.

Note that the filter circuit is not limited to the bandpass filter circuit 18, and for example, a bypass filter circuit (not shown) may be used.

Effects of the Invention The invention as set forth in claim 1 provides a method for transmitting a focus error signal to a focus coil via a drive amplifier based on a focus error signal detected by a light receiving element having a light receiving surface divided into a plurality of parts of an optical pickup and output from a focus error signal detection circuit. a first drive voltage that has a higher frequency than the first drive voltage and that causes a very slight displacement with respect to the amount of movement in the focus direction; superimposes a separate second drive voltage, and measures the signal detection insensitive area related to the dividing line of the light-receiving surface of the light-receiving element from the drive voltage of the signal waveform in which the first drive voltage and the second drive voltage are superimposed. In order to perform By superimposing the two drive voltages, it is possible to obtain a focus error signal with a fine local waveform that is different from the eight-character characteristic of the conventional focus error signal, and the focus error signal waveform including the high frequency waveform can be observed. Therefore, if the influence of the dividing line of the light-receiving element exists, its amplitude becomes small, so that the degree of influence of the dividing line can be measured.

The invention according to claim 2 is the invention according to claim 1,
Since the frequency of the second drive voltage superimposed on the first drive voltage is set so that an amplitude of at least one period or more is generated with respect to the dividing line width of the light receiving surface of the light receiving element, the focused point of the focus error signal is It is possible to observe amplitude fluctuations in the vicinity with high precision, and thereby the influence of the dividing line of the light-receiving element can be detected more accurately.

The invention according to claim 3 is the invention according to claim 2, in which a filter circuit is further connected to the output stage of the focus error signal detection circuit that outputs the focus error signal. By allowing the light to pass through, amplitude fluctuations of the focus error signal near the in-focus point can be measured with even higher precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention of claim 1;
Figure 2 is a waveform diagram showing the two waveforms that are superimposed;
The figure is a waveform diagram showing the state of the waveform of a focus error signal containing high frequency components, FIG. 4 is a circuit diagram showing an embodiment of the invention as claimed in claim 3, and FIG. Figure 6 is a block diagram showing the conventional focus drive circuit, Figure 7 is a circuit diagram showing the conventional focus error signal detection circuit, and Figure 8 is the conventional astigmatism method. FIG. 9 is an explanatory diagram showing the principle of measuring the focus error signal, and FIG. 1O is a circuit diagram showing signal detection using the conventional Knifezi method. FIG. 11 is an explanatory diagram showing the principle of measuring the focus error signal,
FIG. 12 is a waveform diagram showing the waveform of a conventional focus error signal. 7... Light receiving element, 7a... Parting line, 10... Focus error signal detection circuit, 12... Drive amplifier, 1
3... Focus coil, 18... Filter circuit,
A...First drive voltage, B...Second drive voltage, Fo.
... Focus error signal Applicant: Ricoh Co., Ltd. Figure 2

Claims (1)

[Claims] 1. A focus error signal is applied to a focus coil via a drive amplifier based on a focus error signal detected by a light-receiving element having a plurality of divided light-receiving surfaces of an optical pickup and output from its focus error signal detection circuit. A first drive voltage having a predetermined signal waveform, which has a higher frequency than the first drive voltage, and which is different from the first drive voltage and which causes a very small displacement with respect to the amount of movement in the focus direction. A second drive voltage is superimposed, and a signal detection dead area related to a dividing line of the light-receiving surface of the light-receiving element is measured from the drive voltage of the signal waveform obtained by superimposing the first drive voltage and the second drive voltage. A method for measuring signal characteristics of a focus error signal, characterized in that: 2. A claim characterized in that the frequency of the second drive voltage superimposed on the first drive voltage is set so that an amplitude of at least one period or more is generated with respect to the dividing line width of the light-receiving surface of the light-receiving element. 1. The method for measuring signal characteristics of a focus error signal according to 1. 3. Connect a filter circuit to the output stage of the focus error signal detection circuit that outputs the focus error signal, and adjust the frequency of the second drive voltage superimposed on the first drive voltage to the dividing line width of the light-receiving surface of the light-receiving element. 2. The method for measuring signal characteristics of a focus error signal according to claim 1, wherein settings are made such that an amplitude of at least one period or more is generated.