JP2002074845A - Method of controlling waveform equalization circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that an exhaustive search sometimes requires a lot of time and jitter does not converge to the best jitter point in a simple search. SOLUTION: The initial values of an fc and a bst and an initially set jitter value are stored (S111). The fc is fixed and the bst is decreased (S112), and when a monitored jitter value becomes larger than the initially set jitter value (S113→Y), the initial value of the bst and the initially set jitter value are reset at that position (S114). The bst is reduced (S115) also when the monitored jitter values becomes smaller than the initially set jitter value, the jitter values are compared (S116→N→S117) and when the monitored jitter value becomes larger than the initially set jitter value (S116→N), a position having a bst value earlier by one is made to be a provisional convergence point (S118), the fc and the bst are made to be the initial values and the exhaustive search is performed in a specified range to a direction in which both fc and the bst increase (S119), and then the fc and the bst of the best jitter point where the monitored jitter is the smallest are decided as finally set values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DVD (digital
A waveform that is controlled by a waveform equalization circuit that performs waveform equalization on a demodulated signal (RF signal) demodulated from an optical disc on which a signal is recorded at a high density such as a versatile disc) The present invention relates to a method for controlling an equalizing circuit.

[0002]

2. Description of the Related Art Data recorded as pits having different concavities and convexities on an optical disk such as a DVD on which a signal is recorded at a high density is converted into an analog signal (hereinafter referred to as an RF signal) photoelectrically converted by an optical pickup of an optical disk reproducing apparatus. )
Is read as Then, the RF signal is reproduced as a digital signal by A / D conversion. However, the signal output from a reproduction optical system such as an optical pickup has a high-frequency portion attenuated, so that the amplitude of the high-frequency signal is extremely lower than the amplitude (level) of the low-frequency signal. ing.

For this reason, if the signal output from the reproducing optical system is demodulated and reproduced by A / D conversion while keeping the original waveform, the quality of the reproduced signal is extremely deteriorated due to the influence of jitter and the like. Therefore, it is essential to perform signal equalization on the signal output from the reproduction optical system before performing A / D conversion.

FIG. 4 is a diagram schematically showing a reproducing component in an optical disk (recording) reproducing apparatus. Light output from a semiconductor laser of an optical pickup is reflected by the optical disk, and the reflected light is reflected by a photodetector of the optical pickup. 21 and is subjected to photoelectric conversion. The photoelectrically converted analog waveform signal (RF signal) is supplied to a waveform equalizing circuit 22 where the signal is subjected to waveform equalization to remove jitter and the like. Output as a signal.

This photodetector (reproduction optical system) 21
Equalization circuit 2 for equalizing the waveform of the RF signal output from the
2 is set for the purpose of adjusting the frequency characteristics of the reproduction system to flatten the frequency characteristics of the RF signal. Normally, as shown in FIG. 5, it is composed of a combination of a high-order low-pass filter (hereinafter, LPF) 1 and a low-order high-pass filter (hereinafter, HPF) 2, and the cutoff frequency (hereinafter, fc) of each of the filters 1 and 2. By varying two factors, ie, the gain (boost amount: bst), the frequency characteristic of the RF signal is optimized for the reproduction system.

The waveform equalization circuit 22 shown in FIG. 5 has a configuration in which the cutoff frequency (fc) of the output of the LPF 1 and the cutoff frequency (fc) and the gain (bst) of the output of the HPF 2 can be adjusted. I have. The input RF signal is input to LPF1 and HPF2,
It is cut off at the frequency set by the cut-off frequency setting device 4 and separated into a low-frequency part and a high-frequency part.
The high-frequency portion output from the HPF 2 is supplied to a gain adjuster (ATT: attenuator) 3 and a gain setting device 5
The gain of the amplitude is adjusted with the value set by the formula (1), and the adder 17 combines the gain with the low-frequency portion output from the LPF 1 and outputs the signal after waveform equalization.

In this waveform equalizing circuit 22, LPF1, HPF2 when the gain adjustment amount in the gain adjuster 3 is varied.
FIG. 6 shows the output signal characteristics of the (actually the gain adjuster 3) and the waveform equalizing circuit 22. In FIG. 6, the vertical axis represents the signal gain (amplitude value), and the horizontal axis represents the signal frequency. At this time, since the gain of the output signal from the LPF 1 has not been adjusted, the characteristics shown in the graph 8 are obtained regardless of the gain adjustment amount. The output signal from the HPF 2 (actually, the gain adjuster 3) is as shown in a graph 7 when the gain adjustment amount is low, and as shown in a graph 6 when the gain adjustment amount is high. Therefore, the output of the waveform equalization circuit 22 output from the adder 17 is as shown in a graph 10 when the gain adjustment amount is low, and is shown in a graph 9 when the gain adjustment amount is high.
become that way. In this way, the output of the waveform equalizing circuit 22 changes the shoulder characteristic as indicated by the arrow due to the difference in the gain adjustment amount.

FIG. 7 shows the output signal characteristics of the LPF1, HPF2 and the waveform equalizing circuit 22 when the cutoff frequency fc is varied in the waveform equalizing circuit 22. In FIG. 7, the vertical axis represents the signal gain (amplitude value), and the horizontal axis represents the signal frequency. The output signal of the HPF 2 after the gain adjustment (the output from the gain adjuster 3 whose gain is adjusted to bst) is as shown in a graph 11 when the cutoff frequency is low, and a graph when the cutoff frequency is high. It looks like 12. Then, the output signals from the LPF 1 corresponding to each become a graph 13 and a graph 14, respectively. When the cut-off frequency is low, the output signal from the waveform equalization circuit 22 that combines the respective outputs has characteristics as shown in a graph 15 which is a composite signal of the graphs 11 and 13, and the cut-off frequency is high. In this case, the characteristics are as shown in a graph 16 which is a composite signal of the graphs 12 and 14. When the cutoff frequency changes in this manner, the cutoff frequency of the output signal from the waveform equalizing circuit 22 also changes as indicated by the arrow.

[0009] Assuming the changes described above,
By changing both the factors fc and bst, the waveform equalizing circuit 22
It is basically to correct the characteristics of the output signal level from the flat, but actually even if the demodulated signal level is corrected to be flat, the jitter is not always the best. The adjustment is performed not to make the demodulation signal level flat but to aim at the best reproduction system jitter.

[0010] As a method for actually improving the reproduction system jitter, the two factors (fc, bst) are repeatedly changed in a stepwise manner by a fixed amount while monitoring the reproduction system jitter. A method of driving in is adopted.

[0011] As an optimization algorithm that has been conventionally implemented to drive the best jitter,
There are two methods:

First, as a first method, the jitter is monitored for all fc and bst step values within a certain range, and the fc value and bst when the best jitter value is obtained are obtained.
There is an exhaustive search method that uses a value as a set value. As shown in FIG. 8, all the jitter values (numerals in circles) when fc and bst are changed stepwise are obtained, and the jitter value becomes the best point (the number in circles is the most significant). Small value)
The fc value and bst value of the place are set values.

As a second method, an initial value of a step value of fc and bst is set, and one factor value (for example, bst) is set.
With the value of the other factor (here, fc) varied while obtaining a provisional best jitter value within the variable range,
Fix the variable factor value (here fc) that obtained the provisional best jitter value, and fix the factor value that was fixed first (here bst)
To drive to a point with a better jitter value,
There is a simple exploration method. As shown in FIG. 9, the search is performed by changing only fc from the measurement start point, and when the provisional convergence point is determined, the search is performed by changing only bst. In this case, there is an advantage that the search can be completed at a higher speed than in performing the exhaustive search. Note that the order in which fc and bst are variable may be reversed.

[0014]

In a waveform equalizing circuit used in an optical disk reproducing apparatus, the value of a factor such as fc or bst is determined by using an exhaustive search method or a simple search method, so that the jitter of a reproduced signal is optimized. Seeking points,
Actually, variations in the characteristics of the pickup, variations in the time constant of the reproduction system filter, and the type of the optical disk (DVD-ROM or DVD
-R or DVD-RW), the difference between single-layer / double-layer, and the bit recording state differs for each stamper on the disc. are doing. Therefore, in order to reliably identify the jitter best point in consideration of these fluctuation factors, the fc value and the bst value are changed over a wide range each time the optical disc is inserted into the playback device, and the jitter at that time is monitored. Then, it is necessary to obtain and set the fc value and the bst value that are the optimum jitter values.

However, in the above-described optimization algorithm based on the exhaustive search method, when a search is performed over a wide range, the factor value that can obtain the best jitter can be reliably determined. Since the search is performed, it takes an enormous amount of time to monitor the jitter value, and there is a problem that it takes a considerable amount of time to start the reproduction of the optical disk.

In the above-described optimization algorithm based on the simple search method, the factor value can be determined in a short time even if the search is performed in a wide range. In some cases, a factor value that can obtain the best jitter cannot be determined with certainty.

For example, when the simple exploration method is carried out, an initial value having a high fc and a low bst as shown in FIG. 10 or an initial value having a low fc and a high bst as shown in FIG. When set, the final convergence point may be different depending on which of fc and bst is fixed first and the search is performed. In the case shown in FIGS. There is a problem that the factor value does not converge to the best point and a factor value that becomes the jitter best point cannot be obtained.

As shown in FIG. 12, if the jitter reduction direction is toward the jitter best point at all points, even if the optimization algorithm by the simple search method is used,
Although the convergence point converges on the best point irrespective of the setting of the initial value, actually, as shown in FIG. 13, there is a region where the jitter reduction direction is not directed to the jitter best point. Will be different.

Referring to FIG. 14, which shows this in a case where bst is plotted on the x-axis, fc is plotted on the y-axis, and jitter is plotted on the z-axis.
A case where bst is changed after searching by changing fc with bst fixed from A, and fc after bst is changed with fc fixed from initial value B
It can be seen that the convergence point is clearly different from the case where is varied. And it can be seen that the true best point with the smallest jitter is at a further different position.

Therefore, the present invention provides a control method of a waveform equalizing circuit which can complete a search in a shorter time than in the case of using an exhaustive search method, and can converge to a true best point by reliable driving. The purpose is to do.

[0021]

SUMMARY OF THE INVENTION As means for achieving the above object, an object of the present invention is to provide a method for controlling a waveform equalizing circuit as described below.

1. A method for controlling a waveform equalization circuit that can independently adjust a cutoff frequency and a gain adjustment amount, and performs waveform equalization of a demodulated signal from an optical disc.
Detecting the jitter of the output signal of the waveform equalizer circuit when one of the cutoff frequency or the gain adjustment amount is changed, and temporarily convergence of the cutoff frequency and the gain adjustment amount that are the minimum jitter values. Point, the minimum jitter value when the cutoff frequency and the gain adjustment amount are varied in a predetermined range based on the provisional convergence point is detected by an exhaustive search method, and the minimum jitter value detected by the exhaustive search method is A method of controlling a waveform equalization circuit, wherein the cutoff frequency and the gain adjustment amount are used as set values of the waveform equalization circuit.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for controlling a waveform equalizing circuit according to the present invention will be described with reference to FIGS. The waveform equalizing circuit to which the present invention is applied is, for example, a waveform equalizing circuit 22 having a configuration as shown in FIG. 5 used for the reproducing system shown in FIG. Since it has already been described, the description is omitted.

The control method of the waveform equalization circuit according to the present invention is shown in FIG.
As shown in the flowchart of FIG. FIG. 2 is a diagram showing the jitter value with fc on the vertical axis and bst on the horizontal axis, and the number in the circle indicates the jitter value at that position. The numbers in the circles of the solid line indicate the measured jitter, while the values of the jitter in the circles of the dotted line indicate the jitter values that are not measured (although they are actually the jitter values). FIG. 3 shows an actual measurement example.

First, initial values of fc and bst are set, and a jitter value (initial setting jitter value) at the initial value is stored (S11).
1). Here, the initial values of fc and bst are slightly larger than the values of fc and bst at which the demodulated signal level (F characteristic) when playing a standard disc determined for each disc type becomes flat. (For example, a value larger by 4 to 5 steps in fc, bst
Is stored as an initial value for each disc, and the initial value is used in accordance with the type of the inserted disc. The probability that the processing (S113 → Y) is performed can be reduced, and the exploration secretary can be shortened.

Next, the jitter value is monitored while bst is reduced by a fixed amount (one step) while fc is fixed at the initial value (S112). Then, each monitor jitter value when bst is reduced by a predetermined number of steps by one step is compared with the initial set jitter value. If the monitor jitter value is small (S113 → N), the monitor jitter value is not changed. Step S115 and subsequent steps are executed while maintaining the driving direction.

Here, if the monitor jitter value is large when bst is reduced by one step (S113 →
Y), the position where bst is increased by a predetermined number of steps (for example, 7 steps) from the bst initial value is reset as the bst initial value, and the jitter value at that position is stored again as the initial setting jitter value.
(S114), returning to S112. Then, if the monitor jitter value is large even if bst is reduced by one step again from the reset bst initial value, the same processing is repeated again, and S113 →
The loop of Y → S114 → S112 → S113 is repeated until the monitor jitter value decreases.

Then, while the monitor jitter value is smaller than the initially set jitter value, bst is maintained while fc is fixed.
Monitor the jitter value by decreasing it by one step (S1
15) During that time, the latest monitor jitter value is compared while being stored as the initial setting jitter value (S116 → N → S117),
When the monitor jitter value becomes larger than the initially set jitter value (S116 → Y), the position of the bst value of the immediately preceding step is set as a provisional convergence point (S118).

Further, fc of the determined provisional convergence point
With bst as the initial value, an exhaustive search is executed in a predetermined step range (specified range) in a direction in which both fc and bst decrease, and the jitter value is monitored (S119).

Then, the best jitter point having the smallest monitor jitter value is detected from the result of the all-original search within the predetermined step range, and its fc and bst are determined as the final set values (S120).

In the control method of the present invention described above,
fc and bst may be exchanged. However,
Of the wide range of factors for obtaining the best jitter, the most dominant factor is the disc type (DVD-ROM or DVD-ROM).
R or DVD-RW) and the bit recording state differs for each stamper of the disc, and the fluctuation of the jitter best point due to these factors is small in the fc direction and large in the bst direction. Therefore, if the fc initial value is set several steps higher than the fc value that gives the jitter best point, the algorithm invented converges to the jitter best point even if the bst value fluctuates in a considerably large range. As a result, the search in the bst direction with the fc value fixed first can more reliably converge on the jitter best point.

[0032]

The control method of the waveform equalizer according to the present invention has an effect that the search can be completed in a short time, and it is possible to reliably converge to a state where the jitter value is optimal.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an embodiment of a control method of a waveform equalization circuit according to the present invention.

FIG. 2 is a schematic diagram for explaining an embodiment of a method for controlling a waveform equalization circuit according to the present invention.

FIG. 3 is an explanatory diagram showing an example of an embodiment of a method for controlling a waveform equalization circuit according to the present invention;

FIG. 4 is a block diagram illustrating a schematic configuration example of a reproduction system of an optical disk (recording) reproduction device.

FIG. 5 is a block diagram illustrating a configuration example of a waveform equalization circuit.

6 is a graph showing an example of an output waveform of each unit of the waveform equalization circuit shown in FIG.

7 is a graph showing an example of an output waveform of each unit of the waveform equalization circuit shown in FIG.

FIG. 8 is a schematic diagram for explaining an example of exhaustive search.

FIG. 9 is a schematic diagram for explaining an example of a simple search.

FIG. 10 is a schematic diagram for explaining an example of a simple search.

FIG. 11 is a schematic diagram for explaining an example of a simple search.

FIG. 12 is a schematic diagram for explaining an example of a simple search.

FIG. 13 is a schematic diagram for explaining an example of a simple search.

FIG. 14 is an explanatory diagram showing an example of a simple search.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LPF (low-pass filter) 2 HPF (high-pass filter) 3 Gain adjuster (attenuator, ATT) 4 Cut-off frequency setter (fc control) 5 Gain setter (bst control) 17 Adder 21 Photodetector 22 Waveform equalizing circuit 23 A / D conversion circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D044 AB05 AB07 BC03 CC04 FG01 FG05 FG11 5D090 AA01 BB02 CC04 DD03 DD05 EE12 EE17 HH01

Claims (1)

[Claims] 1. A method for controlling a waveform equalization circuit for independently adjusting a cutoff frequency and a gain adjustment amount, and for equalizing a waveform of a demodulated signal from an optical disk, the method comprising: Detecting the jitter of the output signal of the waveform equalizing circuit when one of the values of the gain adjustment amount is changed, the cutoff frequency and the gain adjustment amount that are the minimum jitter values are set as provisional convergence points, The minimum jitter value when the cutoff frequency and the gain adjustment amount are changed in a predetermined range with reference to the convergence point is detected by an exhaustive search method, and the cutoff frequency that becomes the minimum jitter value detected by the exhaustive search method And a method of controlling the waveform equalization circuit, wherein the gain adjustment amount is used as a set value of the waveform equalization circuit.