JP2010027164A - Frequency error detecting method and frequency error detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frequency error detection technique that is resistant to frequency fluctuations.
A voltage-controlled oscillator and a frequency at which a frequency of an input multilevel RF signal is detected (measured) and a frequency error signal representing a difference between the frequency and an output signal frequency from the voltage-controlled oscillator is output. An error detector, a wavelength measuring device that measures a wavelength variation that is the reciprocal of the frequency, and a frequency abnormality determination circuit that determines whether the frequency is abnormal from the measured wavelength variation. A frequency error detection device.
[Selection] Figure 6

Description

  The present invention relates to a frequency error detection method and a frequency error detection device.

  Conventionally, a reproduction signal of an optical disc has been a method of simply binarizing and converting it into a digital signal using a comparator or the like. However, in recent years, in order to reproduce information recorded at high density, the reproduction signal has been digitized using PRML (Partial Response Maximum Likelihood). In order to digitize the reproduction signal using the PRML technique, it is necessary to generate a sampling clock that is phase-synchronized with the reproduction signal of the optical disk. The sampling clock is a clock signal having the frequency of the reference clock signal used when information is recorded on the optical disc, and information is decoded in synchronization with the sampling clock. In the conventional method, the zero cross length of the reproduction signal is measured in order to detect an error between the frequency of the reproduction signal and the frequency of the sampling clock generated by the reproduction circuit. However, when this technology is applied to high-density recording media such as HD DVD, it is difficult to correctly measure the zero cross length due to strong intersymbol interference. Therefore, for example, when detecting the SYNC pattern included in the playback signal, the characteristic pattern (13T: 3T for HD DVD, T indicates the one channel bit length of the reference clock) cannot be detected correctly, or it is erroneously detected. Sometimes happened.

  On the other hand, as means for generating a sampling clock, for example, a unique wavelength (13T for HD DVD) and appearance regularity (1 frame for HD DVD: 1116 channel bits) as in Patent Document 1, for example, For example, a method of detecting a SYNC pattern using each) and obtaining a frequency error from the interval.

However, when the sampling frequency is lower than the channel rate of the input waveform, it becomes difficult to distinguish the longest wavelength from other wavelengths. Furthermore, when the sampling frequency is low enough not to satisfy the sampling theorem, it is conceivable that a long wavelength is measured due to the influence of aliasing noise. As described above, there is a problem in that the operation may become unstable when the frequency fluctuates greatly beyond the assumed frequency fluctuation range.
JP 2008-135139 A

  It is an object of the present invention to provide a frequency error detection technique that is resistant to frequency fluctuations.

  In order to solve the above problems, a frequency error detection device of the present invention detects (measures) a frequency of a voltage controlled oscillator and an input multilevel RF signal, and outputs the frequency and an output signal from the voltage controlled oscillator. A frequency error detector that outputs a frequency error signal representing a difference in frequency between the frequency, a wavelength measuring device that measures a variation in wavelength that is the reciprocal of the frequency, and whether or not the frequency is abnormal based on the measured variation in wavelength. And a frequency abnormality determination circuit for determination.

  According to the present invention, it is possible to obtain a frequency error detection technique that is resistant to frequency fluctuations.

  A first embodiment of the present invention will be described with reference to FIGS. The present invention relates to a method for generating a sampling clock used for decoding reproduction data with respect to an optical disk reproduction apparatus.

FIG. 1 shows a data format of an HD DVD-ROM used in an optical disc apparatus.
The optical disk apparatus is recorded and reproduced in units of data called blocks (or E CC blocks) shown in FIG. 1A, and error correction processing is performed in units of these blocks. The block is provided with an area called V F O at the head, and has 8 3 2 frames following the V F O area.

  In the V F O area, 71-byte single-cycle data is recorded. In addition, if fields such as 2, 4 and 16 bytes of postamble, reserved and buffer following the frame area are included, a total of 9 before and after the frame area.

3 bytes. Each frame is composed of 93 bytes of data. The total amount of data in the block is 77,469 bytes (93 + 93 * 832 bytes).

  FIG. 1B is a diagram showing the data structure of a frame. Each frame has a synchronization pattern of 2 bytes at the head, followed by 91 bytes of data. One byte is composed of 1 2 channel bits (hereinafter simply referred to as bits), the synchronization pattern is composed of 24 bits, and the subsequent data is composed of 1 0 9 2 bits.

  For example, four types of bit patterns are defined in the HDVD as the bit pattern of the synchronization pattern, but all have the same common 18-bit bit pattern.

  FIG. 1 (c) shows this common pattern, which is represented by “01 0 0 0 0 0 0 0 0 0 0 00 1 0 0 1”. This bit sequence is a notation encoded with N R Z I, and “1” indicates that the bit of data before encoding is inverted. Therefore, when expressed as a bit string before encoding, “0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 1” or “1 00 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 ". That is, 13 “1” s continue, followed by 3 “0” s, or 1 3 “0s” continue, followed by 3 “1s”. The bit pattern is a property common to all synchronization patterns. In the present embodiment, this property is used to detect the synchronization pattern. FIG. 2 shows the data format of the HD DVD playback signal. There is 2-byte SYNC data described later.

  Here, regarding the optical disk reproducing method, CAV (Constant Angular Velocity) reproduction for keeping the angular velocity constant will be considered. In CAV playback, when the track jumps from the innermost circumference to the outermost circumference of the disc, the channel rate changes about 2.4 times. When the sampling frequency is lower than the channel rate in this way, the wavelength is measured shorter than the original, so the longest wavelength is detected (distinguish the longest wavelength from other wavelengths: 13T and 11T or less for HD DVD). Is difficult. In addition, the sampling frequency may not satisfy the sampling theorem. For example, in the case of HD DVD, signals of high frequency components such as 2T and 3T correspond to this. High frequency components that do not satisfy the sampling theorem are not only difficult to measure correctly, but also affect low frequency components as aliasing noise. It is difficult to correctly measure the wavelength of the frequency component. Also, due to this influence, it is considered that offset gain control and asymmetry correction are not performed correctly. Under such circumstances, the frequency may not be detected correctly.

  In addition, in the case of a reproduction method using a sub-sampling method with a reduced clock rate, it may be possible to include frequency components that do not satisfy the sampling theorem. Becomes difficult. In addition, it is conceivable that a frequency error is erroneously detected, and the sampling frequency is controlled in the direction opposite to the channel rate, and the frequency detection is similarly difficult.

  On the other hand, this embodiment has a function of determining whether the sampling frequency is fast or slow and bringing the sampling frequency close to an appropriate frequency even when the sampling frequency is greatly different from the channel rate of the input signal. The present invention relates to a frequency detection method or a frequency detector.

  The wavelength of HD DVD is composed of 2T to 11T and 13T, which is a special pattern included in the SYNC pattern, due to run length limitation. Hereinafter, for convenience of explanation, the HD DVD format will be described as an example. However, this embodiment is applicable not only to HD DVD but also to other optical discs such as DVD and frequency detectors in general. FIG. 3 shows an example of the appearance frequency when the wavelength of the RF signal of HD DVD on which random data is recorded is measured. The horizontal axis is the wavelength, and the vertical axis is the appearance frequency. As shown in Fig. 3, due to the characteristics of 8/12 modulation (ETM: Eight to Twelve Modulation), HD DVD data has a higher appearance frequency of high frequency components and a lower frequency of appearance as it becomes lower frequency components. It is in.

  Therefore, in the present embodiment, the frequency of occurrence of each wavelength is measured, and when the sampling frequency is greatly different from the channel rate of the input signal, the frequency control is correctly performed and the measurement is performed in a synchronized state. The direction in which the sampling frequency is to be controlled is determined from the difference in the frequency of appearance of the wavelengths. When the sampling frequency is significantly different from the channel rate of the input signal and normal frequency control is difficult, the frequency is changed in an appropriate direction based on the determination result.

  FIG. 4 is an example of the wavelength measurement result when the sampling clock is 1/2 slower than the HD DVD RF signal channel rate. The horizontal axis is the wavelength, and the vertical axis is the appearance frequency. In this case, since the sampling frequency is slow, it is measured as 1T, in which high frequency components such as 2T and 3T do not originally exist. In addition, low frequency components such as 13T that are necessarily present in the SYNC pattern are hardly measured. Thus, when the measured wavelength dispersion and average value are small and the appearance frequency is biased toward the high frequency component, the sampling frequency is considered to be too slow with respect to the channel rate.

  On the other hand, FIG. 5 shows an example of the wavelength measurement result when the sampling clock is twice as fast as the channel rate of the HD DVD RF signal. The horizontal axis is the wavelength, and the vertical axis is the appearance frequency. In this case, since the sampling frequency is high, the appearance frequency of high-frequency components such as 2T and 3T is reduced, and wavelengths that do not exist originally such as 12T and 14T are measured. Thus, when the measured wavelength dispersion and average value are large and the appearance frequency is biased toward the low frequency component, the sampling frequency is considered to be too fast for the channel rate.

  If the frequency error detector cannot detect the frequency or the possibility of false detection is increased by detecting the abnormality of the sampling frequency using the characteristics of the frequency of appearance of such a wavelength, the frequency in the correct direction Control can be performed.

<Configuration of optical disc apparatus>
An example of the configuration of the optical disc apparatus according to the present embodiment will be described with reference to FIG. In FIG. 6, an optical disk device 1 is a device that reads information from an optical disk medium D. Main components are a pickup head (PUH) 11, an A / D converter (ADC) 12, a phase comparator 13, and a frequency error. It has a detector 14, a loop filter 15, a VCO (Voltage Controlled Oscillator) 16, an adaptive equalizer 17, a maximum likelihood decoder 18, and the like.

  The pickup head 11 reproduces a signal corresponding to information recorded on the optical disk medium D, and receives a laser light source that irradiates the optical disk medium D with laser light and a laser beam that receives the laser light reflected from the optical disk medium D. (Not shown). The reproduction signal output from the light receiver is amplified by the reproduction amplifier 11b to become a reproduction RF signal, and is further guided to the A / D converter 12 via the pre-waveform equalizing means 11c.

  The A / D converter 12 is an element that performs A / D conversion on the input reproduction RF signal and outputs a digital RF signal (multi-value RF signal). This digital RF signal is a multivalued digital value output at substantially constant time intervals.

  A / D conversion in the A / D converter 12 is controlled by a control signal output from a VCO (voltage controlled oscillator) 16. That is, the A / D conversion cycle (time interval) is determined based on the oscillation frequency of the VCO 16.

  The output of the A / D converter 12 is connected to the input of an adjustment mechanism 12b (a kind of amplifier) that adjusts the offset (zero level / slice level) and amplitude of the input reproduction RF signal, and is adjusted by the adjustment mechanism 12b. The reproduced RF signal is configured to be a signal corrected by the next asymmetry correction 12c.

  The adaptive equalizer 17 is a filter that equalizes the multilevel RF signal into a PR (Partial Response) waveform. The adaptive equalizer 17 includes a transversal filter and the like, functions as a waveform equalizer, corrects reproduction distortion, and adjusts the offset (zero level / slice level) and amplitude of the reproduction RF signal. Are output to the maximum likelihood decoder 18.

  The maximum likelihood decoder 18 is composed of a Viterbi decoder or the like, and is configured to decode the data equalized by the adaptive equalizer 17. The output of the maximum likelihood decoder 18 is used as digital demodulated data. The output of the maximum likelihood decoder 18 is also fed back to the adaptive equalizer 17.

The phase comparator 13 is a circuit that compares the phases of the multilevel RF signal output from the maximum likelihood decoder 18 and the output signal (not shown) from the VCO 16 and outputs a phase difference.
The frequency error detector 14 detects (measures) the frequency of the multilevel RF signal input from the A / D converter 12 and outputs a frequency error signal representing the difference between this frequency and the frequency of the output signal from the VCO 16. Circuit. The frequency error detector 14 also outputs a frequency error detection signal used as an error information control signal for controlling whether or not the output frequency error signal is used in the loop filter 15. Details of the internal configuration of the frequency detector 14 will be described later.

  The loop filter 15 is a circuit that generates a voltage for controlling the VCO 16 based on the phase error output from the phase comparator 13 and the frequency error output from the frequency error detector 14.

The VCO 16 is an oscillation circuit that oscillates at a frequency corresponding to the control voltage output from the loop filter 15 and functions as a control signal generator.
A basic flow will be described for the following explanation. First, regarding wavelength measurement, for example, the wavelength can be measured for each mark / space as shown in FIG. Since the next-generation DVD is ultra-high-density recording, the DC level of the relatively short T-length reproduction RF signal is strongly influenced by the preceding and following mark / space patterns (T-length). In addition, PRML uses the fact that a signal is distorted by the interference of a previous signal, and intentionally adds correlated interference. For this reason, it is not possible to correctly detect one mark / space section simply by detecting the crossing of signal levels in the vicinity of the average DC level.

  At this time, a waveform that does not exceed the thresholds TH_H and TH_L is not the longest wavelength included in the SYNC pattern, and is not measured. By measuring the wavelength in this way, it is possible to reduce wavelength measurement errors due to reasons such as not zero-crossing or exceeding the threshold. The wavelength measurement may be any method that can measure the longest wavelength of the SYNC pattern correctly and does not measure a wavelength longer than the SYNC pattern. This is performed to take out a SYNC pattern (sync pattern, sync signal waveform) and control the time interval of A / D conversion in the A / D converter 12 based on the sync pattern.

  In addition to the above, in addition to the frequency error detector 14, a wavelength measuring device 14a for measuring wavelength variation and a frequency abnormality determining circuit 14b are provided. Thereby, the wavelength of the input RF signal is measured, and the abnormality of the sampling frequency is detected from the appearance frequency. When an abnormality is detected, the loop filter 15 is controlled to change the sampling frequency to a range where the frequency can be detected.

  A mounting example for detecting a frequency abnormality from the appearance frequency of the measured wavelength will be described with reference to a flowchart of FIG. When the wavelength X is measured (steps S71 and 72), the number of times of measurement is incremented (step S73), and it is compared whether the wavelength is the threshold value n or less and the threshold value m or more (steps S74 and 75). At this time, if n or less and m or more, the measurement counter is incremented (steps S76 and 77). This is repeated for a certain period (step S78). At this time, it is desirable to set a period in which the SYNC pattern which is the longest wavelength is always included a certain number of times. In FIG. 7, the appearance frequency when the wavelength is measured N times is measured. At this time, it is difficult to measure the wavelength when performing frequency detection using stored data such as defects due to dirt or scratches on the disc, recording defects, unrecorded signals on recordable media, DVD-RAM headers, etc. Is confirmed, it has a function of returning the measurement counter, nT, and mT measurement counters to the initial state (step S79). This is to prevent erroneous determination of frequency detection when the wavelength longer than the longest wavelength included in the SYNC pattern is measured, or when the wavelength cannot be measured correctly due to a small amplitude. As means for confirming such a situation where wavelength measurement is difficult, for example, there is a technique described in JP-A-P2005-166121.

After that, if a high frequency component that should not exist in the standard is measured from the nT counter value (1T in HD DVD) to a large extent (step S7a), this is considered to be too low for sampling. Control is performed so as to increase the frequency (step S7b). Although it is the threshold value, 1T does not exist, so it can be set in accordance with the wavelength measurement accuracy when it is synchronized with the channel rate, for example, when it greatly exceeds it. In addition to simply setting the number of 1T, for example, when the appearance frequency of 1T exceeds 2T and 3T, it can be determined that the distribution is large and biased toward high frequency components.

  Next, if there are many low-frequency components (12T or higher components that do not exist in HD DVD) as well as high-frequency components (step S7c), confirm that the high-frequency components are not included first. Therefore, it is unlikely that this situation has occurred because of an alias that does not satisfy the sampling theorem, and it can be determined that the sampling frequency is too high (step S7d). Although this is a threshold for determining that there are too many components of 12T or more, this should basically not include wavelengths other than the SYNC pattern, and can be estimated to some extent from the wavelength measurement period.

  If this is not the case, it is considered that the frequency control can be performed correctly, and the frequency control by the frequency abnormality detection circuit is not performed. Finally, the wavelength measurement count, nT, and mT measurement counters are reset (step S7e), and the process ends. By repeating this series of operations, it is possible to constantly monitor the case where the frequency is far away and drive it to an appropriate range.

  As another example of the present embodiment, as shown in FIG. 8, when a situation in which wavelength measurement is difficult is confirmed, the measurement number counter, nT, and mT measurement counter are not updated (step S89). A configuration may be adopted. In this case, although there is an influence of a value measured in a situation where wavelength measurement is difficult, since the measured value so far is held, it is possible to detect a frequency abnormality more quickly. Also, as shown in FIG. 9, the wavelength measurement counter detects that the sampling frequency is high (step S9c) before confirming the completion of N times of measurement (step S98), and lowers the sampling frequency (step S9d). You can take it.

  Further, when detecting that the frequency is far away, either one may be detected. In this case, it may be configured to always perform the opposite control. For example, as shown in FIG. 10, if a wavelength longer than the threshold value m is not sufficiently detected (N in step S9c) while measuring the wavelength N times (step S98), it is determined that the frequency is significantly slow and unconditionally. It is good also as a structure which raises a frequency (step S10b). Depending on the detection range and mechanism of the frequency error detector, there is a possibility that the frequency abnormality cannot be detected depending on the written data. For example, if the measurement period is not sufficient, a correct distribution cannot be obtained, and there may be a case where the basic distribution is not complied with, for example, there are almost no high-frequency components that should have a high appearance frequency and only low-frequency components. Specifically, if the data other than the SYNC pattern is composed of 11T, 1T is not detected until the sampling clock becomes 1/11, so the frequency control may be performed depending on the configuration of the frequency error detector. It may not work properly. As described above, when the normal operation of the frequency error detector is not recognized, the sampling frequency may be increased. As a determination criterion when the normal operation of the frequency error detector is not recognized, it can be determined that the frequency control is not performed for a certain period or more.

  In addition, HD DVD has a feature that 2T does not continue more than 6 times, so considering this, since 2T x 5 times is 3T or more, all wavelengths other than the SYNC pattern are 2T. Next, assuming that the shortest is 3T, the wavelength average per frame can be calculated as follows.

(2T x 5 times + 3T) / 6 ≒ 2.17
1 frame: 1116 channel bits. Since the SYNC pattern is 24 channel bits, the data area is 1092 channel bits. However, VFO area is not included.
As a result, the minimum average length is 2.17, so this may be used as a reference, and if the average value is lower than that, the sampling frequency may be increased, and abnormality detection or protection may be applied with the average value.
In addition, as shown in FIG. 11, instead of the number of wavelength measurements, another measurement period such as a timer may be used as the measurement period (step S118).
In this way, it is possible to measure the variation in the appearance frequency of the measurement wavelength and detect an abnormality in the oscillation frequency of the sampling clock. It has the following features.
・ The reference wavelength is 1T or less and 12T or more, but it may be changed according to the wavelength measurement accuracy and range.
In the explanation, HD DVD is mainly used for explanation, but it is a technology that can be used in general optical discs such as DVD, CD, Blu-ray and frequency error detectors.

-Frequency anomalies may be detected by observing wavelength variations using dispersion and average values. Moreover, you may combine the said method and these.
The frequency abnormality detection circuit may be provided with a function of not performing frequency control, notifying the detected information to the outside such as a control MPU, and performing initialization processing such as resetting the sampling frequency.

・ If the frequency error detector is equipped with a wavelength measuring device, it may be used as well.
・ In consideration of the case where the influence of the waveform shaping circuit such as offset / gain control and asymmetry correction is large, the measured waveform may be used immediately after the ADC.

As an effect of the embodiment, a stable frequency control device can be configured by detecting that the sampling frequency is greatly deviated from the channel rate.
• The frequency detection range can be improved when the sampling clock is low relative to the channel rate. The wider the frequency detection range, the higher the frequency can be withdrawn because the frequency can be controlled independently using the frequency detector without the presence of firms and other functions. This is particularly effective when track jumps occur frequently and the frequency fluctuates greatly.

・ The frequency detection range is improved when sampling at a low rate (subsampling) such as half rate. As a result, it is expected to be easy to handle high speed, reduce power consumption, reduce circuit scale, and improve design ease (especially analog circuits such as ADC).

-If the sampling frequency falls outside the frequency detection range, such as when a frequency error is erroneously detected, and the frequency control is not performed correctly, the correct frequency control direction can be determined, and it can return independently.

In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement in various modifications.
Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements according to different embodiments may be appropriately combined.

The figure which shows an example of the data format of the data reproduced with the apparatus which concerns on this invention. The data format figure of the HD DVD playback signal concerning the same embodiment. The wavelength and the example of appearance frequency of the random data of the embodiment. The example of a wavelength measurement result in case the sampling clock of the same embodiment is 1/2 late. The example of a wavelength measurement result in case the sampling clock of the embodiment is twice as fast. The block block diagram which shows the optical disk reproducing device structural example of the embodiment. The operation | movement flow of the frequency abnormality determination circuit used for the embodiment. Modification 1 (retaining value) used in the embodiment. Modification 2 used in the embodiment (frequency control is performed when mT or more is detected). Modification 3 used in the same embodiment (increase sampling frequency when measuring N times). Modification 4 used in the same embodiment (change the measurement count to a timer).

Explanation of symbols

  DESCRIPTION OF SYMBOLS D ... Optical disk, 1 ... Optical disk apparatus, 11 ... Optical pick-up, 12 ... A / D converter, 13 ... Phase comparator, 14 ... Frequency error detector, 14a ... Wavelength measuring device, 14b ... Frequency abnormality determination circuit, 15 ... Loop Filters, 16 ... VCO, 17 ... adaptive equalizer, 18 ... maximum likelihood decoder.

Claims (7)

A voltage controlled oscillator;
A frequency error detector that detects (measures) the frequency of the input multi-value RF signal and outputs a frequency error signal that represents a difference between the frequency and the frequency of the output signal from the voltage controlled oscillator;
A wavelength measuring instrument for measuring variation in wavelength that is the reciprocal of the frequency;
A frequency error detection circuit comprising: a frequency abnormality determination circuit that determines whether or not the frequency is abnormal from the measured variation in wavelength.   2. The frequency error according to claim 1, wherein when the sampling frequency is relatively large with respect to the input frequency, the frequency error acts to determine the level of the sampling frequency based on the frequency of appearance of the wavelength of the input waveform. Detection device.   The frequency error detection apparatus according to claim 2, further comprising a function of approaching an appropriate sampling frequency according to the determined result.   4. The frequency error detection apparatus according to claim 3, further comprising a function of approaching an appropriate sampling frequency using an average value or dispersion of wavelengths of an input waveform.   2. A function for discarding information such as the appearance frequency, average, and dispersion of wavelengths when a state in which an expected wavelength cannot be detected correctly is detected, and performing a re-measurement when the wavelength is in a state in which it can be detected correctly. The frequency error detection device described in 1.   When detecting the state where the expected wavelength cannot be detected correctly, it stops updating the information such as frequency, average, and dispersion of the wavelength, and when the wavelength can be detected correctly, it has a function to restart measurement. The frequency error detection apparatus according to claim 1. Voltage controlled oscillation,
Detect (measure) the frequency of the input multilevel RF signal, and output a frequency error signal representing the difference between this frequency and the frequency of the output signal generated by the voltage controlled oscillation,
Measure the wavelength variation that is the reciprocal of the frequency,
A frequency error detection method comprising performing frequency abnormality determination for determining whether or not the frequency is abnormal from the measured variation in wavelength.

Images