JPS6370932A - Track error signal detection circuit for optical disk device - Google Patents

Abstract

PURPOSE:To detect a track error signal, and to suppress the occurrence of offset with a simple constitution by generating a diagonal differential signal and a sum total signal from the outputs of a quadruple detector, deciding the direction of an error from the phase difference between the said two signals, then switching the output. CONSTITUTION:The four outputs of the quadruple light receiving element 8 that receives the reflected light from the medium of an optical disk device are added up to make the total signal Sa, and one of the diagonal two of the said outputs is subtracted from the other to make the diagonal differential signal Sd. Comparators 16, 17 respectively decide whether the total signal Sa and the diagonal differential signal Sd respectively are positive or negative, and a D-flip-flop circuit 18 latches the sign of the diagonal differential signal Sd i.e. the direction of the shifting at the time of rising or ending of the total signal Sa. Thereafter, a sign inverter 19 makes the diagonal differential signal Sd or -Sd depending on the decided direction of shifting. A multiplier 20 multiplies the original waveform signal Sd by the waveform Sd or -Sd after the said sign switching, to generate Sd<2> or -Sd<2>. The characteristic shown by broken lines as waveform (j) which is a track error signal, is obtained, by passing the signal of wave form (j) through a low-pass filter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention provides a track error signal detection circuit for an optical disk device, in order to provide a circuit that has a simple structure but is less prone to offset. A diagonal difference signal Sa and a sum signal Sd are generated from the outputs of the divided detectors, the direction of the error is determined from the phase difference between the two, and based on this determination, the diagonal difference signal, which only shows the absolute value of the error, is processed by a multiplier. By switching between Sa2 and -3a'', it is detected as a track error signal.

(Industrial Application Field) The present invention relates to an optical disc device, and more particularly to a track error signal detection circuit.

FIG. 4 shows a principle diagram of a conventional optical disc device.

In the figure, reference numeral 1 denotes a disk-shaped recording medium, which is rotated by a spindle motor 2. -4 Light from a semiconductor laser 3 is focused onto the recording medium 1 by an objective lens 4, resulting in a minute spot 5 (right side in the figure). (see enlarged view), and the light receiving element 7 converts the intensity of reflected light generated by the information pits 6 concentrically or spirally recorded on the recording medium 1 into an electrical signal.

In addition to the read-only type, in which the information bit 6 is already attached at the time of manufacturing the recording medium 1, only a groove (pre-group) is added, and a strong power light is shined on or between the grooves. There is a write-once type in which the device itself records information by destroying or discoloring 1, and some write-once types use magneto-optical effects instead of destruction or discoloration to enable erasing.

In any case, the minute light spot 5 is relatively easy to create and has a feature of high recording density. It is necessary to achieve just the right focus, and track control is essential in addition to focus control.

This uses a servo mechanism that detects and feeds back each error, and in trunk control, an error detection method with a simple mechanism and few off-cents is desired.

This trunk error detection method includes a pre-group method in which the depth of information bit 6 is set to λ/8, a three-beam method in which the beam is divided into three, and a heterodyne method in which the diagonal difference signal is held at the rising and falling edges of the information signal. There are laws, etc.

Although the pregroup method has a simple configuration, it has the disadvantage that offset is likely to occur due to the tilt of the recording medium 1 and the beam shift (movement of reflected light on the light receiving element) due to movement of the objective lens 4. Although the offset is less likely to occur in the heterodyne method, the optical system is complicated and the power is dispersed, which is a disadvantage.The heterodyne method is less likely to cause an offset, but the circuit is complicated.

The present invention is based on the concept of the heterodyne method, and is intended to simplify the circuit and adjustment.

[Conventional technology]

FIG. 5 is a diagram showing the distribution of the amount of reflected light depending on the relative position of the information pit on the medium and the incident light spot. 5 and 6 in the figure. correspond to the same numbers in FIG. 4, respectively.

Reference numeral 8 shows the light-receiving surface of the light-receiving element 7 in FIG. 4 divided into four parts, and the amount of light received corresponding to each light-receiving surface is P+, Pi h.

Hail on P4. Note that the shaded areas of the incident light become dark.

Further, B indicates an on-track state, and A and C indicate a state shifted to the left and right, respectively. On the other hand, since the disk is rotating, it changes over time from the state t to the state tz-t3. Therefore, the reflected light is divided into four parts, and the diagonals of the light-receiving element are added to each other, and the difference is calculated ((
pt+p3) -(P2+P4) (hereinafter abbreviated as diagonal difference signal)], and by comparing the values at the time of 1+, the direction and magnitude of the deviation can be determined. The same is true at time t3, but the sign is reversed compared to time tl.

FIG. 6 shows a block diagram of the conventional heterogain method.

In the figure, each output of a four-part light receiving element 8 that receives reflected light 9 from a medium of an optical disk device is a sum signal S.
a, and a subtracter 11 that subtracts the sum of diagonal positions to create a diagonal difference signal Sd.

12 is a rising pulse generator that generates pulses in response to the rising signal of the summation signal Sa; 13 is a falling pulse generator that generates pulses in response to the falling signal of the summation signal Sa; 14a and 14b are two independent sample holder circuits; , the sample holder circuit 14a is sampled by the output of the rising pulse generator 12, and the sample holder circuit 14b is sampled by the output of the falling pulse generator 13.
sampled by the output of

Reference numeral 15 is composed of a subtracter that creates a difference between the outputs of both sample holder circuits 14a and 14b.

FIG. 7 is an operational waveform diagram of the conventional example, and each waveform of S+1-e corresponds to the waveform of the same sign position written in FIG.

Since the falling point of the summation signal Sa corresponds to t in FIG. 5, and the rising point corresponds to t, pulse waveforms a and b are generated at each point, and the diagonal difference signal Sd
If these are held in separate sample holder circuits 14a and 14b, error signals with different polarities, such as waveforms c and d, can be obtained. Furthermore, by outputting the difference between waveforms c and d from the subtracter 15, a track error signal e with the in-phase error removed is obtained.
is obtained.

[Problem that the invention seeks to solve]

The heterodyne method described above has a simple optical system, and even if the beam moves on the photodetector, there is little effect on the diagonal difference ((PI+P3) - (pz+p*)),
When Pl decreases, P3 increases] Although it does not easily cause offset, it has the disadvantage that the circuit is complicated and adjustment is difficult.

In particular, since the frequency of information bit 6 is recorded on the order of MHz, sample holder 1 enables high-speed processing.
4 was required, and the only option was to create a complicated circuit or use a special and expensive IC. Furthermore, there is a drawback that if the timing of the sample pulse is shifted as shown by the broken lines of the waveforms Sa and ad in FIG. 7, the anger level decreases.

The present invention was created in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a track error signal detection circuit that has a simple circuit configuration but is less prone to offset.

[Means for solving problems]

As shown in FIG. 1, the track error signal detection circuit of the optical disc device of the present invention collects a sum signal Sa of each output of a four-division light receiving element 8 that receives reflected light from a medium of the optical disc device, and a pair of each output. In a track error signal detection circuit that uses a diagonal difference signal Sd for subtracting the sum of angular positions, a first comparator 16 determines whether the sum signal Sa is positive or negative, and a first comparator 16 determines whether the diagonal difference signal Sd is positive or negative. Second to do
a comparator 17, a flip-flop circuit 18 that latches the output of the second comparator 17 when the output of the first comparator 16 rises or falls; Sign switching circuit 19 for inverting the polarity of
, the output of the code switching circuit 19 and the diagonal difference signal Sci
and a multiplier 20 that multiplies by.

[Effect]

FIG. 2 shows an example of waveforms of each part of the circuit shown in FIG. In the figure, when looking at the diagonal difference signal Sd, its envelope shows the absolute value of the tracking error signal. Therefore, by determining the direction of deviation and selecting either a positive envelope or a negative envelope, a tracking error signal is obtained.

The direction of the shift can be determined from the sign of the diagonal difference signal Sd at the rise or fall of the summation signal Sa.

Therefore, in the present invention, first the sum signal Sa and the diagonal difference signal Sd are each determined to be positive or negative by a comparator, and then the D-type flip-flop circuit 18 determines the sign or shift of the diagonal difference signal Sd at the rise or fall of the sum signal Sa. Latch the direction (see waveforms f to h). Then, the code switch 19 changes the diagonal difference signal Sd to Sd or -Sd depending on the direction of the determined deviation (see comparison of waveforms Sd and i).

Furthermore, if the original waveform Sd is multiplied by the sign-switched waveform Sd or -3d by the multiplier 20, then Sd'' or =
Sd'' (see comparison of waveform Sd, i and j).

If this waveform j signal is passed through a low-pass filter, waveform j
The characteristic shown by the broken line is the track error signal.

However, from the multiplier 20 onward, a so-called operational amplifier circuit is used, and since the frequency band is low, the result as shown by the broken line can be obtained even without a low-pass filter. In addition, the code changer 19
Since it is sufficient to multiply Sd by -1 or 1, the circuit is the same as the multiplier 20.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make the explanation of the configuration and operation easier to understand, the same parts will be given the same reference numerals throughout and the repeated explanation will be omitted.

FIG. 3 shows a circuit example of a code converter and a multiplier used in the present invention. This circuit is called a double-balanced amplifier, and since it is also used in television detection circuits, high-speed, dedicated ICs are available at low cost. In Fig. 3, 21 is a constant current source, and the output is obtained as follows. If 0N10FF control is performed, the multiplier 20 and the code switch 19 become code switchers, so the circuits are the same.Also, this circuit is a differential type, and the input shown in FIG. I didn't show it.

Each inverted value of the direction judgment output Q and the inverted value of the diagonal difference signal Sd are required, but they can be obtained from a normal differential amplifier or D-type flip-flop circuit without the need for a special circuit. .

In addition, the digital part of this circuit is used only for direction determination, so even if the phases of Sd and Sa are slightly shifted, the detection result will not change, and the high-speed part has an analog configuration, so the effect of overshoot on the digital signal will not be affected. It is relatively easy to speed up the process without any problems. Furthermore, if a dedicated IC is used as described above, the circuit configuration is simple and adjustment is easy.

〔Effect of the invention〕

As described above in detail, according to the track error signal detection circuit for an optical disc device of the present invention, a detection circuit that does not cause offset and has a simple structure can be realized.

Note that the present invention requires rising and falling signals of information pits, and the present invention cannot be applied to a long groove (group) write-once type. However, in these write-once types, information such as track numbers is usually preformed in dozens of locations around the circumference of the medium, called an ID section or preformat section. By using the pre-group method, which allows a track error signal to be obtained even from a group section where there is no ID section, and the present invention, which is applicable only to the ID section, it is possible to compensate for each other's shortcomings.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of the present invention, Figure 2 is an operational waveform diagram of the present invention, Figure 3 is a circuit example of a code switcher and multiplier used in the present invention, and Figure 4 is the principle of a conventional optical disc device. Figure 5 shows the light intensity distribution of reflected light depending on the relative position of the information pit on the medium and the incident light spot, Figure 6 is a diagram showing the configuration of the conventional heterodyne method, and Figure 7 shows the operation of the conventional example. A waveform diagram is shown. In FIG. 1, 8 is a four-division type light receiving element, 16 is a first comparator, 17 is a second comparator, 18 is a D-type flip-flop circuit, 19 is a code switching circuit, 20 is a multiplier, and Sa is a summation Signal and Sd indicate diagonal difference signals, respectively. Figure 1 Reto 3gi): +14 Riichi Nakazu'F 52F Man〉Baku Figure 2 Outside Needle 81 Flank 5 Inn t'77f Fin Erection Temporary Route Example Figure 3 is Water 4 (Tekin 7 Device - Hara rY mouth Figure 4
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Claims (1)

[Claims] A summation signal Sa of each output of a four-part light receiving element (8) that receives reflected light from a medium of an optical disc device, and a diagonal difference signal that subtracts the sum of diagonal positions of each output. In the track error signal detection circuit using Sd, a first comparator (16) determines whether the sum signal Sa is positive or negative; a second comparator (17) determines whether the diagonal difference signal Sd is positive or negative; a flip-flop circuit (18) that latches the output of the second comparator (17) when the output of the first comparator (16) rises or falls; A code switching circuit (19) for inverting the polarity of the difference signal Sd, and a multiplier (20) for multiplying the output of the code switching circuit (19) by the diagonal difference signal Sd. Track error signal detection circuit for optical disc devices.