JPH06101209B2 - Tracking circuit - Google Patents

Description

The present invention relates to a tracking circuit suitable for use in a sample servo type optical disc device or the like.

[Outline of Invention]

In the present invention, when the sampling value of the tracking error signal becomes equal to or larger than the window centered on the previous sampling value, it is limited to the window value.

[Background technology]

In a sample servo type optical disc, servo byte sections are provided at predetermined intervals, and wobbled pits for tracking are formed in advance in each servo byte section as prepits. The data is recorded in the data section following the servo byte section. A tracking error signal is generated by sampling the level difference between the RF signals corresponding to the two wobbled pits, and this sampling value is held until the next servo byte section.

If there is a defect in the wobbled pit or if there is dust in the vicinity of it, an abnormal value will be sampled.In the conventional circuit, the sampled value is compared with a predetermined reference value, and a value above the reference value is detected. When sampled, the previous sampled value is held as it is.

[Problems to be solved by the invention]

In this way, the conventional circuit only outputs the previous sampling value as it is when the sampling value exceeds the range of the predetermined reference value.Therefore, in order to enable tracking of a disc with large eccentricity, the reference value The range of must be increased to some extent. However, in that case, sampling of an abnormal value cannot be prevented, and the tracking servo may be missed in the defective servo byte section. On the contrary, if the range of the reference value is made small, it becomes impossible to track a disc with large eccentricity.

The present invention has been made in view of such circumstances, and enables tracking of a disc with a large eccentricity,
It prevents abnormal values from being sampled and enables accurate tracking.

[Means for solving problems]

The tracking circuit of the present invention includes a window generation circuit for generating a window of a first width centered on a previous sampling value of a tracking error signal generated by sampling an RF signal at a predetermined cycle, and a tracking error signal present. Of the first comparison circuit for comparing the sampling value of the first comparison circuit with the window and the output of the first comparison circuit is selected when the output of the first comparison circuit is within the window of the first width. A selector for selecting a window value when the window is not within the first width, a second comparison circuit for comparing the output of the selector with a reference value for defining the second width window, and a second comparison circuit. And a latch circuit for latching the output of the selector only when the output is within the window of the second width.

[Action]

The tracking error signal is generated by sampling the RF signal at a predetermined cycle. The window generation circuit adds / subtracts a value of a predetermined width to the previous sampling value to generate a window. The first comparison circuit compares the current sampling value with the window and controls the selector according to the comparison result. The selector selects the current sampling value when it is within the window range, and selects the window value when it is out of the range. The output of the selector is compared with a predetermined reference value by the second comparison circuit. When it is within the range of the reference value, the current sampling value is latched by the latch circuit. If it is out of the range, the previous sampling value is output as it is from the latch circuit.

Therefore, it is possible to limit abrupt changes in the tracking error signal, and at the same time, it becomes possible to track tracks on a disk having a large eccentricity.

〔Example〕

FIG. 1 shows a block diagram of the tracking circuit of the present invention. A value obtained by sampling the difference between the RF signals corresponding to the wobbled pits in each servo byte section is input to the latch circuit 1 from the terminal 11 and latched at the timing of the clock supplied from the terminal 12. The latch value of the latch circuit 1 is supplied to the comparison circuit 4.

The latch circuit 5 uses the previous sampling value (time t _{1 in} FIG. 2).
Value L ₁ ) in the window generation circuit 2
This latch value (L _1), the window data of a predetermined width which is supplied from the terminal 13 (± W ₁₎ and acceleration (deceleration) calculated to produce the window (L ₁ ± W ₁₎ of a predetermined width. The comparison circuit 4 compares this window with the current sampling value latched by the latch circuit 1 (value L ₂ at time t ₂ in FIG. ₂ ) and outputs a signal corresponding to the comparison result to the selector 3. Selector 3
A sampling value (L ₂₎ is the window (L ₁ ± W ₁₎ sampling value when in a range of (L ₂₎ is selected, the window value when in the out of range (L ₁ + W ₁₎ or (L ₁ It is switched by the output of the comparison circuit 4 so that the one closer to the sampling value (L ₂ ) is selected from −W ₁ ). That is, the sampling value is selected when it is within the range of the window, but the sampling value is limited to the window value when it is outside the range.

The value selected by the selector 3 is input to the latch circuit 5 and latched at the timing of the clock supplied from the terminal 14.

The output of the latch circuit 5 is supplied to the comparison circuit 7. The reference value (± W ₂ ) is also supplied to the comparison circuit 7 via the terminal 19. The output (value L ₂ ) of the latch circuit 5 is the reference value (absolute value)
When it is larger than W ₂ or smaller than −W ₂ , the comparison circuit 7 generates a warning signal from the terminal 10. When this warning signal is input, the protection circuit 8 does not output a clock to the latch circuit 6. Therefore, the latch circuit 6 has the previous sampling value (L ₁ )
Is directly output to terminal 15.

Further, the protection circuit 8 inhibits the latch of the latch circuit 6 when a signal indicating the loss of synchronization is input from the terminal 17.

When the output of the latch circuit 5 is larger than the reference value −W _{2 and} smaller than W ₂ , the protection circuit 8 outputs the clock supplied from the terminal 18 to the latch circuit 6. As a result, the sampling value (L ₂ ) output from the latch circuit 5 is latched by the latch circuit 6 and output.

〔effect〕

As described above, according to the present invention, the current sampling value is compared with a window of a predetermined width centered on the previous sampling value, and further compared with a predetermined reference value.
The window can be set relatively small and the reference value can be set relatively large. Therefore, it is possible to trace a track having a large eccentricity while preventing a rapid change in the tracking error signal due to noise or the like, and it is possible to prevent a gradual large change in the tracking state.

[Brief description of drawings]

FIG. 1 is a block diagram of a tracking circuit according to the present invention, and FIG.
The figure is a waveform diagram of the tracking error signal. 1 …… Latch circuit 2 …… Window generation circuit 3 …… Selector 4 …… Comparison circuit 5,6 …… Latch circuit 7 …… Comparison circuit 8 …… Protection circuit 11 to 19 …… Terminal

Claims (1)

[Claims] 1. A window generation circuit for generating a window of a first width centered on a previous sampling value of a tracking error signal generated by sampling an RF signal at a predetermined cycle, and a current tracking error signal. A first comparison circuit for comparing the sampling value of the first comparison circuit with the window, and selecting the current sampling value when the output of the first comparison circuit is within the window of the first width, A selector for selecting the value of the window when the output of the comparison circuit is not within the window of the first width, and a second comparison circuit for comparing the output of the selector with a reference value defining the window of the second width. A latch circuit for latching the output of the selector only when the output of the second comparison circuit is within the window of the second width.