Method for determining DC level of AC signal and DC offset of the same

Abstract

A method for determining a direct current (DC) level involved in an alternating current signal is provided. The alternating current signal is transmitted from an amplifier to an A/D (analog-to-digital) converter. When any of the extreme values of the alternating current signal is beyond the input range of the A/D converter, the alternating current signal is shifted to make both of the peak and bottom values located within the input range of the A/D converter. Then, the real extreme values are realized according to the shift level(s), the relative peak and bottom values realized after the shifting procedure, and the input range of the A/D converter. Finally, the DC level is determined according to the real peak and bottom values.

Description

[(Amax+Amin)/2]×Vmin/Dmin;or
[(Amax+Amin)/2]×(|Vmin|+|Vmax|)/(|Dmin|+|Dmax|).

The present invention can be illustrated according to the following example for more detailed description. For example, the A/D converter 42 has an input range from −5V (Vmin) to 5V (Vmax), and a resolution of 255. Thus, Dmin and Dmax are digitally defined as −127 and 127, respectively. When the first level L1 is set to be 5×(20/127) Volts, and the relative bottom value Rmin is detected to be −125 by the bottom value detector 432, the digital value Amin of the bottom value is calculated as −145, i.e. −125−[(5×(20/127))×(−127/−5) ]. When the second level L2 is set to be 5×32/127 Volts and the relative peak value Rmax is detected to be 120 by the peak value detector 431, the digital value Amax of the peak value is then calculated as 152, i.e. 120+[5×(32/127)×(127/5)]. Therefore, the DC offset level involved in the tracking error signal TE is computed by:
[(152+(−145))/2 ]×5/127;or
[(152+(−145))/2]×(−5)/(−127);or
[(152+(−145))/2]×(|−5 |+|5|)/(|−127 |+|127|),
which all equal to 0.138 Volts.

After the DC level involved in the tracking error signal TE is determined, the voltage drift thereof can be adjusted to a zero level by the operational amplifier 41 in response to a level control signal from the tracking balance device 433. Since the voltage drift is correctly computed, the above-mentioned drawbacks in the prior art can be effectively avoided.

In conclusion, the present invention covers a method for realizing an extreme value A of an alternating current signal transmitted from an amplifier to an A/D converter, wherein the extreme value is beyond an input range of the A/D converter, and the method includes the following steps:

• (i) Shifting the alternating current signal by a level L to define a relative alternating current signal having a relative extreme value R being the level L away from the extreme value A and located within the input range of the A/D converter; and
• (ii) Calculating the extreme value A of the alternating current signal according to the level L, the relative extreme value R, and the input range of the A/D converter, such that,
  A=R+[L×(D/V)] when the extreme value is a peak value; or
  A=R−[L×(D/V)] when the extreme value is a bottom value,
  where V is a lower/upper voltage limit of the input range of the A/D converter, and D is a digital value of the lower/upper limit of the input range.

Further, the present invention also covers a method for offsetting a voltage drift of an alternating current signal transmitted from an amplifier to an A/D converter, wherein the alternating current signal has a non-zero DC level and at least one extreme value beyond an input range of the A/D converter, and the method includes the following steps:

• (i) Shifting the alternating current signal in a first manner to define a first relative alternating current signal having a first relative extreme value located within the input range of said A/D converter, wherein the first shifting manner is either an up shift or a down shift such that the first relative extreme value of the first relative alternating current signal is at a first level away from the first original extreme value of the alternating current signal;
• (ii) Calculating a first original extreme value of the alternating current signal according to the first level, the first relative extreme value, and the input range of the A/D converter;
• (iii) Shifting the alternating current signal in a second manner to define a second relative alternating current signal having a second relative extreme value located within the input range of the A/D converter, wherein the second shifting manner shifts to a direction opposite to the first shifting manner such that the second relative extreme value is at a second level away from the second original extreme value;
• (iv) Calculating a second original extreme value of the alternating current signal according to the second level, the second relative extreme value, and the input range of the A/D converter;
• (v) Calculating a DC offset level according to the first and second original extreme values of the alternating current signal; and
• (vi) Offsetting the voltage drift of the alternating current signal according to the DC offset level.

The present invention is illustrated by referring to a method for realizing extreme values of a tracking error signal when both extreme values thereof are beyond an input range of the A/D converter. It is understood by a person skilled in the art that the present invention also suitable for a tracking error signal having only one extreme value beyond an input range of the A/D converter.

While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

Claims

1. A method for determining a direct current (DC) offset level of an alternating current (ac) signal, said alternating current signal being transmitted from an amplifier to an analog-to-digital (A/D) converter and having a first extreme value which is beyond an input range of said A/D converter, said method comprising steps of:

shifting said alternating current signal by a predetermined first level to define a first relative alternating current signal having a first relative extreme value being said predetermined first level away from said first extreme value and lying within said input range of said A/D converter;

realizing said first extreme value according to said predetermined first level, said first relative extreme value, and said input range of said A/D converter;

shifting said alternating current signal by a predetermined second level to define a second relative alternating current signal having a second relative extreme value being said predetermined second level away from said second extreme value and lying within said input range of said A/D converter;

realizing said second extreme value according to said predetermined second level, said second relative extreme value, and said input range of said A/D converter; and

determining said DC offset level according to said first extreme value and said second extreme value.

2. The method according to claim 1 wherein one of said first and second extreme values is a peak value, and the other is a bottom value.

3. The method according to claim 1 wherein the steps of shifting said alternating current signal are respectively performed by said amplifier in response to a level control signal.

4. The method according to claim 3 wherein said predetermined first level, said first relative extreme value and said input range of said A/D converter are digitally operated to realize a digital value of said first extreme value, said predetermined second level, said second relative extreme value and said input range of said A/D converter are digitally operated to realize a digital value of said second extreme value, and said DC offset level is determined according to said digital value of said first extreme value and said digital value of said second extreme value by a digital signal processor.

5. The method according to claim 4 wherein said level control signal is outputted from said digital signal processor.

6. The method according to claim 1 wherein said first and second relative extreme values are converted into a digital bottom value Rmin and a digital peak value Rmax by said A/D converter, and detected by a bottom and a peak detectors of a digital signal processor, respectively.

7. The method according to claim 6 wherein a digital value Amin of said first extreme value is defined by Rmin−[L1×(Dmin/Vmin)], and a digital value amax of said second extreme value is defined by Rmax×[L2×(Dmax/Vmax)] in which L1 is said predetermined first level, Dmin is a digital value of a lower limit of said input range, Vmin is a lower voltage limit of said input range, L2 is said predetermined second level, Dmax is a digital value of an upper limit of said input range, and Vmax is an upper voltage limit of said input range.

8. The method according to claim 7 wherein said DC offset level is defined by:

[(amax+Amin)/2]×Vmax/Dmax.

9. The method according to claim 7 wherein said DC offset level is defined by:

[(amax+Amin)/2]×Vmin/Dmin.

10. The method according to claim 7 wherein said DC offset level is defined by:

[(amax+Amin)/2]×(|Vmin|+|Vmax|)/(|Dmin|+|Dmax|).

11. A method for offsetting a voltage drift of an alternating current signal transmitted from an amplifier to an analog-to-digital (A/D) converter, said alternating current signal having a non-zero direct current (DC) level and at least one extreme value beyond an input range of said A/D converter, said method comprising steps of:

shifting said alternating current signal in either an up or a down shift of a first level to define a first relative alternating current signal having a first relative extreme value of said first relative alternating current signal located within said input range of said A/D converter;

realizing a first original extreme value of said alternating current signal according to said first shifting manner, said first relative extreme value of said first relative alternating current signal, and said input range of said A/D converter;

shifting said alternating current signal in an opposite direction of a second level to define a second relative alternating current signal having a second relative extreme value of said second relative alternating current signal located within said input range of said A/D converter;

realizing a second original extreme value of said alternating current signal according to said second shifting manner, said second relative extreme value of said second relative alternating current signal, and said input range of said A/D converter;

determining a DC offset level according to said first and second original extreme values of said alternating current signal; and

offsetting said voltage drift of said alternating current signal according to said DC offset level;

wherein a digital value Amin of said first original extreme value is defined by Rmin−[L1×(Dmin/Vmin)], and a digital value amax of said second original extreme value is defined by Rmax+[L2×(Dmax/Vmax)], in which Rmin and Rmax are digital bottom value and digital peak value converted from said first and second relative extreme values, respectively, L1 is said first level, Dmin is a digital value of a lower limit of said input range, Vmin is a lower voltage limit of said input range, L2 is said second level, Dmax is a digital value of an upper limit of said input range, and Vmax is an upper voltage limit of said input range.

12. The method according to claim 11 wherein said non-zero DC level is adjusted to a zero level in the step of offsetting said voltage drift.

13. The method according to claim 11 wherein said DC offset level is defined by a formula selected from a group consisting of:

[(amax+Amin)/2]×Vmax/Dmax;

[(amax+Amin)/2]×Vmin/Dmin; and

[(amax+Amin)/2]×(|Vmin|+|Vmax|)/(|Dmin|+|Dmax|).

14. An optical storage tracking apparatus for controlling a tracking operation of an optical storage system, the optical storage system including a pickup head for picking up data from an optical storage medium, the apparatus comprising:

means for transmitting an alternating current (ac) signal from an amplifier to an analog-to-digital (A/D) converter, the alternating current signal having a first extreme value which is beyond an input range of the A/D converter;

means for shifting the ac signal by a predetermined first level to define a first relative ac signal having a first relative extreme value being the predetermined first level away from the first extreme value and lying within an input range of the A/D converter;

means for realizing the first extreme value according to the predetermined first level, the first relative extreme value, and the input range of the A/D converter;

means for shifting the ac signal by a predetermined second level to define a second relative ac signal having a second relative extreme value being the predetermined second level away from the second extreme value and lying within the input range of the A/D converter;

means for realizing the second extreme value according to the predetermined second level, the second relative extreme value, and the input range of said A/D converter; and

means for determining the DC offset level according to the first extreme value and the second extreme value.

15. A tracking control system for an optical storage system, the tracking control system comprising:

an optical pickup head having a plurality of light receiving components configured to produce output signals when receiving light reflected from an optical disk;

an analog-to-digital (A/D) converter;

an amplifier coupled to the optical pickup head and the A/D converter, the amplifier being configured to—

generate a tracking error signal in response to one or more of the output signals, wherein the tracking error signal is an alternating current (ac) signal, and wherein the tracking error signal has a bottom value and a peak value, the bottom value and the peak value being outside an input range of the A/D converter;

shift the tracking error signal by a predetermined first level to define a first relative tracking error signal having a first relative extreme value within an input range of the A/D converter;

calculate a first original extreme value of the tracking error signal according to the first level, the first relative extreme value, and the input range of the A/D converter;

shift the tracking error signal by a predetermined second level to define a second relative tracking error signal having a second relative extreme value within the input range of the A/D converter;

calculate a second original extreme value of the tracking error signal according to the second level, the second relative extreme value, and the input range of the A/D converter; and

calculate a direct current (DC) offset level according to the first and second original extreme values of the tracking error signal; and

a tracking balance device coupled to the A/D converter and the amplifier and configured to offset the voltage drift of the tracking error signal according to the DC offset level.