Patent Application
20100027392
The present invention relates to apparatuses and methods for calibrating an optical storage device, and more particularly, to apparatuses and methods for calibrating the optical storage device by utilizing a data-to-data jitter meter.
In high-density optical storage devices such as DVD, Blu-ray or HD-DVD, jitter plays an important role in evaluating and determining data quality (i.e., quality of radio frequency (RF) signals). However, in the optimal power calibration (OPC) area or any power calibration area (PCA) on an optical disc, because pits on the OPC area are formed by driving a laser diode with different recording powers, the quality of the RF signal from the OPC area is unstable. Therefore, when calibrating the recording power in the OPC area, an unstable jitter measuring result may occur due to the poor quality of the RF signal.
It is therefore an objective of the claimed invention to provide an apparatus comprising a wobble PLL and a data-to-data jitter meter, and related methods to solve the above-mentioned problem.
According to one embodiment of the present invention, a method for calibrating an optical storage device comprises: providing a clock signal; obtaining a plurality of data-to-data jitter values of a plurality of radio frequency (RF) signals according to the clock signal; and determining a minimum jitter value among the plurality of data-to-data jitter values
According to another embodiment of the present invention, an apparatus for calibrating an optical storage device comprises a clock generator, a jitter meter, and a first calculation unit. The clock generator is utilized for providing a clock signal; the jitter meter is utilized for obtaining a plurality of data-to-data jitter values of a plurality of radio frequency (RF) signals according to the clock signal; and the first calculation unit is utilized for determining a minimum jitter value among the plurality of data-to-data jitter values.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
Please refer to
In an optimal power calibration (OPC) area on the optical disc, pits on each sector (or each circle) are typically formed by different recording powers, and an optical pick-up head receives the information from the OPC area to generate a plurality of radio frequency (RF) signals and a wobble signal, wherein the RF signals and the wobble signal is respectively derived corresponding to stored data and the structure of the disc. It is noted that quality of the RF signals is related to recording power.
The wobble signal is inputted into the wobble PLL 110 to generate a clock signal CLK, where a period of the clock signal CLK is 1T. The period “T” is defined in specifications of optical storage devices, and pit lengths are represented by this symbol (such as 2T-9T). The equalizer 120 receives the RF signals and generates an equalized RF signal RF_EQ. Then, the DD jitter meter 130 obtains a plurality of DD jitter values of the RF signals according to the equalized RF signal RF_EQ and the clock signal CLK. Finally, the calculation unit 140 determines a minimum jitter value among the DD jitter values, and thus an optimal recording power is determining according to the minimum jitter value.
In this embodiment, the clock signal CLK is generated according to the wobble signal. In addition, taking 1T as the period of the clock signal CLK is a preferred example, the period of the clock signal CLK can also be less than 1T, for example 1T divided by a positive integer.
Compared with the conventional data-to-clock jitter meter, the DD jitter meter 130 in the apparatus 100 can determine the jitter value without locking the phases between the RF signal and the clock signal CLK. It is noted that the quality of the RF signal is affected by recording power easily, and thereby the data PLL derived from the RF signals loses lock probably. In contrast, the effective wobble signal (disc structure determined) is far less in frequency comparing to RF signal, and such that after some signal processing (for example, band-pass filter), the quality of generated wobble signal in general is not affected by recording power easily. Thus, the wobble PLL 100 has wider stable region in recording power comparing to data PLL. And then DD jitter meter 130 can generate more valid jitter values with using wobble PLL than data PLL (since jitter is related to PLL stability). Accordingly, using wobble PLL 100 in the curve fitting to find the minimum jitter value will generate more stable results than using data PLL does.
Ti=3T+σ1−σ2;
The above-mentioned steps are repeated to calculate a plurality of pulse widths Ti, and an average pulse width Ta is determined according to these pulse widths Ti. Then, DD jitter values are calculated according to width errors between each pulse width Ti and the average pulse width Ta, i.e. (Ti-Ta). It is noted that the above steps for calculating the DD jitter value are for illustrative purposes only. The DD jitter value can also be determined according to other methods, such as the pulse width standard deviation. As long as the pulse widths Ti are generated from the above formula, these alternative representations of jitter value are all within the scope of the present invention.
After the plurality of DD jitter values are determined, the calculation unit 140 generates a fitting-curve according to the DD jitter values, and an extreme value of the fitting-curve is set as a minimum jitter value.
It is noted that, in the OPC area, pits are formed with lengths from 2T to 9T, and the RF signals are generated correspondingly. Thus, the DD jitter values correspond to 2T-9T RF signals. However, because the 2T RF signal is unstable, the DD jitter values corresponding to the 2T RF signal are generally worse than the DD jitter values corresponding to 3T-9T RF signals. Therefore, the calculation unit 140 can also generate a fitting-curve of the DD jitter values, exclusive of jitter values of the 2T RF signal (i.e., the DD jitter values correspond to 3T-9T RF signals). An extreme value of this fitting-curve is set as a minimum jitter value, and a power corresponding to the minimum jitter value serves as the optimal recording power.
It is noted that, if the 2T RF signal is stable in the future, the 2T RF signal will be allowable to be taken for generating the fitting-curve.
In addition, the equalizer 120 is an optional device, and can be removed from the apparatus 100, thus the DD jitter meter 130 obtains a plurality of DD jitter values of the RF signals according to the RF signal and the clock signal CLK. The equalizer 120 behaves as a frequency shaper to filter out out-band noises, and boost in-band signals, thus the situation of jitter can be improved. However, when the quality of jitter is acceptable, the equalizer 120 can be removed.
Moreover, a so-called “walking-OPC” method is utilized to dynamically adjust the recording power of the laser during the writing process to ensure a greater quality consistency. However, in order to save the processing time and to calibrate the recording power on-the-fly according to the DD jitter values, several well-known parameters “beta target” and “beta slope” for OPC are utilized to calibrate the recording power on-the-fly.
Please refer to
Functions of the wobble PLL 410, the equalizer 420, the DD jitter meter 430 and the first calculation unit 440 are respectively the same as the functions of the wobble PLL 110, the equalizer 120, the DD jitter meter 130 and the calculation unit 140 shown in
It is noted that definitions of the “beta” is described by many references, such as the specifications of the optical storage devices, therefore, introduction is omitted here.
Please refer to
ΔP=(β−βtarget)/beta slope
In addition, since quality of RF signals is also influenced by servo parameters (such as defocus, tracking error, tilt or spherical aberration), thus the implementations of the apparatus 100 can also be utilized to calibrate servo parameters, such as
Please refer to
Therefore, the user can use the apparatus 600 for calibration to obtain a specific optimal servo parameter. Also, the user can obtain a set of optimal servo parameters sequentially according to the servo parameters calibration by utilizing the apparatus 600. For example, the user can adjust the servo parameters, defocus, tracking error, tilt and spherical aberration sequentially, and the optimal servo parameters of the defocus, tracking error, tilt and spherical aberration are obtained respectively after the calibration.
Regarding the operations of the apparatus 600, the wobble signal is inputted into the wobble PLL 610 to generate a clock signal CLK, where a period of the clock signal CLK is 1T. The equalizer 620 receives the RF signals and generates an equalized RF signal RF_EQ according to the clock signal CLK. Then the DD jitter meter 630 obtains a plurality of DD jitter values of the RF signals according to the equalized RF signal RF_EQ and the clock signal CLK. Finally, the calculation unit 640 determines a minimum jitter value among the DD jitter values, and an optimal servo parameter combination (or a servo parameter) is determining according to the minimum jitter value.
It is noted that the apparatus 100 shown in
Briefly summarized, according to the apparatuses and the methods for calibrating an optical storage device, a wobble PLL and a DD jitter meter are utilized to generate a plurality of DD jitter values, and an optimal recording power is determined according to the DD jitter values. Moreover, the optimal recording power is utilized to generate two parameters “beta target” and corresponding “beta slope”, these two parameters are for calibrating the recording power on-the-fly. In addition, an optical pick-up head utilizes the generated optimal recording power to write data onto a segment of the optical disc, and servo parameters are calibrated in the segment.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
