METHOD FOR CONTROLLING LASER POWER OF AN OPTICAL PICKUP UNIT
A method for controlling laser power of an optical pickup unit (OPU) includes: providing a first relationship between the laser power and a driving parameter, wherein the driving parameter is utilized for driving a laser diode (LD) of the OPU, and the first relationship corresponds to a first temperature; utilizing a temperature-related model to convert the first relationship into a second relationship between the laser power and the driving parameter, wherein the second relationship corresponds to a second temperature; and storing the first relationship for being utilized at the first temperature, and storing the second relationship for being utilized at the second temperature.
This application claims the benefit of U.S. Provisional Application No. 60/991,185, which was filed on Nov. 29, 2007, and entitled “AUTO POWER CALIBRATION STRUCTURAL”.
BACKGROUNDThe present invention relates to power calibration of an optical pickup unit (OPU) with respect to temperature during a mass production phase of an optical disc drive, and more particularly, to a method for controlling laser power of an OPU.
Regarding the control over an OPU of an optical disc drive in the related art, a conventional automatic power calibration (APC) circuit can be utilized for controlling the laser power of a laser diode (LD) during a normal operation of the optical disc drive, e.g. a reading/writing operation. When the conventional APC circuit reaches a steady state during the normal operation mentioned above, the laser power corresponds to a target command that is sent to the conventional APC circuit.
It is a goal for the conventional APC circuit to control the laser power to be a specific power value corresponding to the target command, in order that the laser power varies in accordance with the target command. Thus, how to prepare a precise relationship between the laser power and the target command during a mass production phase of the optical disc drive has become an important issue
A conventional method for deriving the relationship between the laser power and the target command typically comprises measuring the laser power by utilizing a power meter, and collecting data sets of the laser power and the target command. However, the cost of the power meter is high, and the corresponding tooling and labor costs of a power calibration station for implementing this method are also required. In addition, these costs will be multiplied according to the number of production lines. Furthermore, other issues such as the differences between respective power calibration stations may arise.
According to the related art, an OPU vendor may design a front-end photo diode (PD) in an OPU, and the system manufacturers (e.g. an optical disc drive manufacturer) may use the front-end PD as a replacement for the power meter. The measurement result from the front-end PD is outputted through a front-end PD output (FPDO), and can be referred to as the FPDO value. As the OPU vendor typically provides a few data points for stating the relationship between the laser power and the FPDO value, interpolation operations are required for deriving the laser power corresponding to other data points on a predicted curve passing through the few data points mentioned above. As a result, the whole process of deriving a precise relationship between the laser power and the target command is slowed down due to the interpolation operations.
Thus, no matter whether the calibration in the power calibration station is implemented by utilizing the power meter or the FPDO, the corresponding costs such as time, tooling and/or labor costs are required. Moreover, there is little awareness of the inaccuracy due to temperature variation during the normal operation. As a result, the calibration is often performed at only an arbitrary temperature.
Even if the inaccuracy due to the temperature variation during the normal operation is noticed, performing the calibration in the power calibration station with respect to different values of temperature will be cost-ineffective for most system manufacturers utilizing the related art methods.
Therefore, the control over the laser power will certainly be inaccurate in a normal operation when the temperature varies. A novel method is therefore required for solving the related art problems, such as the inaccuracy due to the temperature variation, and the tradeoff between the costs and the performance.
SUMMARYIt is therefore an objective of the claimed invention to provide a method for controlling laser power of an optical pickup unit (OPU), in order to solve the above-mentioned problems.
An exemplary embodiment of a method for controlling laser power of an OPU comprises: providing a first relationship between the laser power and a driving parameter, wherein the driving parameter is utilized for driving a laser diode (LD) of the OPU, and the first relationship corresponds to a first temperature; utilizing a temperature-related model to convert the first relationship into a second relationship between the laser power and the driving parameter, wherein the second relationship corresponds to a second temperature; and storing the first relationship for being utilized at the first temperature, and storing the second relationship for being utilized at the second temperature.
An exemplary embodiment of a method for controlling laser power of an OPU comprises: providing a first relationship between the laser power and a driving parameter, wherein the driving parameter is utilized for driving an LD of the OPU, and the first relationship corresponds to a first temperature; providing a second relationship between the laser power and the driving parameter, wherein the second relationship corresponds to a second temperature; and storing the first relationship for being utilized at the first temperature, and storing the second relationship for being utilized at the second temperature.
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, which refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not in function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another 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 Step 912, a first relationship between the laser power and a driving parameter is provided, where the driving parameter is utilized for driving a laser diode (LD) of the OPU to control the laser power, and the first relationship corresponds to a first temperature such as room temperature. The relationships between the laser power (which can be simply referred to as power) and the driving parameter (e.g. voltage) are different according to temperature values. For example, the first relationship can be depicted as one of the curves labeled “Middle Temperature” in the temperature-related models respectively shown in
According to this embodiment, the vertical axis (labeled “Power”) shown in
In practice, the first relationship is typically derived by measuring the laser power and the driving parameter at the first temperature. According to this embodiment, a target command carrying a specific value can be first applied to an automatic power calibration (APC) circuit for controlling the laser power. When the APC circuit reaches a steady state at the first temperature, the laser power and the driving parameter are measured in order to derive the first relationship. Typically, when partial information of the first relationship is given (e.g. a slope or an offset of a curve of the first relationship), only measuring a single data point comprising a specific value of the laser power and a specific value of the driving parameter may be enough for deriving the first relationship, where such a data point can be utilized for depicting a curve of the first relationship with the horizontal and the vertical axes respectively representing the driving parameter and the laser power.
For example, the target command carrying a specific value V1 can be first applied to the APC circuit. When the APC circuit reaches a steady state at the first temperature, the laser power and the driving parameter are measured to derive the single data point P1. Thus, the single data point P1 can be utilized for deriving the first relationship. In this embodiment, the single data point P1 is illustrated on the curves labeled “Middle Temperature” in the temperature-related models respectively shown in
According to a variation of this embodiment, the single data point P1 is illustrated on the curves labeled “Low Temperature” in the temperature-related models respectively shown in
Sometimes, measuring two data points may be required, where the two data points are derived according to the same method as that for deriving the single data point with regard to different values of the target command, respectively. For example, the target command carrying a first value V1-1 can be first applied to the APC circuit. When the APC circuit reaches a steady state at the first temperature, the laser power and the driving parameter (such as voltage) are measured to derive a first data point P1-1. Afterward, the target command carrying a second value V1-2 can be applied to the APC circuit. When the APC circuit reaches a steady state at the first temperature, the laser power and the driving parameter (such as voltage) are measured to derive a second data point P1-2. Thus, the first data point P1-1 and the second data point P1-2 can be utilized for deriving the first relationship.
In Step 914, a temperature-related model is utilized, such as one of the two temperature-related models shown in
As shown in
According to this embodiment, no matter whether the temperature-related model shown in
The method for deriving the single data point P2 at the second temperature is similar to that for deriving the single data point P1 at the first temperature except for the ambient temperature during the measurement. For example, the target command carrying a specific value V2 can be first applied to the APC circuit. When the APC circuit reaches a steady state at the second temperature, the laser power and the driving parameter are measured to derive the single data point P2. Thus, the data point P2 can be utilized for deriving the sufficient information of the temperature-related model.
According to a variation of this embodiment, measuring two data points at the second temperature may be required in order to derive sufficient information of the temperature-related model. In this variation, after deriving the sufficient information of the temperature-related model, whether the temperature-related model shown in
For example, the target command carrying a first value V2-1 can be first applied to the APC circuit. When the APC circuit reaches a steady state at the second temperature, the laser power and the driving parameter are measured to derive a first data point P2-1. Afterward, the target command carrying a second value V2-2 can be applied to the APC circuit. When the APC circuit reaches a steady state at the second temperature, the laser power and the driving parameter are measured to derive a second data point P2-2. Thus, the first data point P2-1 and the second data point P2-2 can be utilized for deriving the sufficient information of the temperature-related model.
In Step 916, the first relationship for being utilized at the first temperature is stored, and the second relationship for being utilized at the second temperature is stored. In practice, the various representatives of the first relationship and the second relationship can be stored in a non-volatile memory such as a Flash memory. For example, the representatives can be curve coefficients of the curves representing the first relationship and the second relationship, respectively. In addition, the representatives in another example can be one or more data points for each of the first relationship or the second relationship. Additionally, the representatives in another example can be one or more curve coefficients together with one or more data points.
According to this variation, a method for transforming a voltage difference ΔVX(T1, T2) corresponding to a channel X (e.g. one of the channels 1 to N) into a voltage difference ΔVY(T1, T2) corresponding to a channel Y (e.g. another of the channels 1 to N) is further provided, in order to make sure the method mentioned above can be widely applied. As a result, some special situations can be covered. The voltage differences ΔVX(T1, T2) and ΔVY(T1, T2) mentioned above respectively have two indexes T1 and T2 representing two different values of temperature T, and are typically defined as follows:
ΔVX(T1, T2)=VoltX(T2)−VoltX(T1); and
ΔVY(T1, T2)=VoltY(T2)−VoltY(T1);
where VoltX(T) represents a voltage value of the LD driving voltage in the channel X at temperature T, and VoltY(T) represents a voltage value of the LD driving voltage in the channel Y at temperature T.
According to this variation, the voltage difference ΔVY(T1, T2) can be derived by the following equation:
ΔVY(T1, T2)=(Gain(X)/Gain(Y))*ΔVX(T1, T2);
where Gain(X) and Gain(Y) represent the channel gain functions of the channels X and Y, respectively.
For example, the voltage difference ΔVX(T1, T2) is derived from the method shown in
where the above equation can be utilized for deriving an additional relationship between the laser power and the driving parameter in the channel Y.
As the channels X and Y mentioned above may represent any two of the channels 1 to N, the relationships between the channel gain functions Gain(1), Gain(2), . . . , and Gain(N) and the voltage differences respectively corresponding to the channels can be expressed, in general, by utilizing the following equation:
ΔVchannel 1*Gain(1)=ΔVchannel 2*Gain(2)= . . . =ΔVchannel N*Gain(N);
where ΔVchannel 1, ΔVchannel 2, . . . , and ΔVchannel N represent the voltage differences corresponding to the channels 1 to N, respectively.
In another variation of the first embodiment, the voltage values VoltX(T) and VoltY(T) of the LD driving voltage can be replaced with corresponding current values CurrX(T) and CurrY(T) of the LD driving current mentioned above, and the voltage differences ΔVX(T1, T2) and ΔVY(T1, T2) can be replaced with corresponding current differences ΔCX(T1, T2) and ΔCY(T1, T2), respectively.
As a result of applying the method mentioned above, the present invention indeed provides proper control over laser power in the normal operation when the temperature varies. In contrast to the related art, by performing the relationship conversion and measuring of a few data points as disclosed in the embodiment(s) and/or variations mentioned above, the present invention method greatly saves the costs required for the calibration in the power calibration station, and therefore solves the tradeoff between the costs and the performance.
It is another advantage of the present invention that, when the laser power control should be implemented with respect to a large number of values of temperature, the relationships corresponding to these values of temperature can be efficiently derived according to the embodiments and/or variations mentioned above.
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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A method for controlling laser power of an optical pickup unit (OPU), the method comprising:
- providing a first relationship between the laser power and a driving parameter, wherein the driving parameter is utilized for driving a laser diode (LD) of the OPU, and the first relationship corresponds to a first temperature;
- utilizing a temperature-related model to convert the first relationship into a second relationship between the laser power and the driving parameter, wherein the second relationship corresponds to a second temperature; and
- storing the first relationship for being utilized at the first temperature, and storing the second relationship for being utilized at the second temperature.
2. The method of claim 1, wherein the driving parameter represents an LD driving voltage for controlling an LD driving current of the LD.
3. The method of claim 1, wherein the driving parameter represents an LD driving current of the LD.
4. The method of claim 1, wherein the step of providing the first relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a specific value to an automatic power calibration (APC) circuit for controlling the laser power; and
- when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive the first relationship.
5. The method of claim 1, wherein the step of providing the first relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a first value to an automatic power calibration (APC) circuit for controlling the laser power, and when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive a first data point;
- applying a target command carrying a second value to the APC circuit, and when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive a second data point; and
- utilizing the first and second data points to derive the first relationship.
6. The method of claim 1, wherein the temperature-related model corresponds to curves having respective slopes with respect to different temperatures.
7. The method of claim 1, wherein the temperature-related model corresponds to parallel curves with respect to different temperatures.
8. The method of claim 1, further comprising:
- measuring the laser power and the driving parameter at the second temperature to derive information of the temperature-related model.
9. The method of claim 8, wherein the step of measuring the laser power and the driving parameter at the second temperature to derive the information of the temperature-related model further comprises:
- applying a target command carrying a specific value to an automatic power calibration (APC) circuit for controlling the laser power; and
- when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive the information of the temperature-related model.
10. The method of claim 8, further comprising:
- applying a target command carrying a first value to an automatic power calibration (APC) circuit for controlling the laser power, and when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive a first data point;
- applying a target command carrying a second value to the APC circuit, and when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive a second data point; and
- utilizing the first and second data points to derive the information of the temperature-related model.
11. The method of claim 1, wherein the first and second relationships correspond to a first channel; and the method further comprises:
- utilizing the first and second relationships to derive an additional relationship between the laser power and the driving parameter in a second channel.
12. The method of claim 11, wherein the driving parameter represents an LD driving voltage; and the step of utilizing the first and second relationships to derive the additional relationship between the laser power and the driving parameter in the second channel further comprises:
- transforming a first voltage difference into a second voltage difference;
- wherein the first voltage difference represents a difference between different voltage values of the LD driving voltage in the first channel at the first and the second temperatures, respectively;
- wherein the second voltage difference represents a difference between different voltage values of the LD driving voltage in the second channel at the first and the second temperatures, respectively.
13. The method of claim 11, wherein the driving parameter represents an LD driving current of the LD; and the step of utilizing the first and second relationships to derive the additional relationship between the laser power and the driving parameter in the second channel further comprises:
- transforming a first current difference into a second current difference;
- wherein the first current difference represents a difference between different current values of the LD driving current in the first channel at the first and the second temperatures, respectively;
- wherein the second current difference represents a difference between different current values of the LD driving current in the second channel at the first and the second temperatures, respectively.
14. A method for controlling laser power of an optical pickup unit (OPU), the method comprising:
- providing a first relationship between the laser power and a driving parameter, wherein the driving parameter is utilized for driving a laser diode (LD) of the OPU, and the first relationship corresponds to a first temperature;
- providing a second relationship between the laser power and the driving parameter, wherein the second relationship corresponds to a second temperature; and
- storing the first relationship for being utilized at the first temperature, and storing the second relationship for being utilized at the second temperature.
15. The method of claim 14, wherein the driving parameter represents an LD driving voltage for controlling an LD driving current of the LD.
16. The method of claim 14, wherein the driving parameter represents an LD driving current of the LD.
17. The method of claim 14, wherein the step of providing the first relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a specific value to an automatic power calibration (APC) circuit for controlling the laser power; and
- when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive the first relationship.
18. The method of claim 14, wherein the step of providing the first relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a first value to an automatic power calibration (APC) circuit for controlling the laser power, and when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive a first data point;
- applying a target command carrying a second value to the APC circuit, and when the APC circuit reaches a steady state at the first temperature, measuring the laser power and the driving parameter to derive a second data point; and
- utilizing the first and second data points to derive the first relationship.
19. The method of claim 14, wherein the step of providing the second relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a specific value to an automatic power calibration (APC) circuit for controlling the laser power; and
- when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive the second relationship.
20. The method of claim 14, wherein the step of providing the second relationship between the laser power and the driving parameter further comprises:
- applying a target command carrying a first value to an automatic power calibration (APC) circuit for controlling the laser power, and when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive a first data point;
- applying a target command carrying a second value to the APC circuit, and when the APC circuit reaches a steady state at the second temperature, measuring the laser power and the driving parameter to derive a second data point; and
- utilizing the first and second data points to derive the second relationship.
Type: Application
Filed: Aug 26, 2008
Publication Date: Jun 4, 2009
Inventors: Hsiao-Yuan Chi (Taipei City), Chih-Ching Chen (Miaoli County), Chia-Wei Liao (Hsinchu County)
Application Number: 12/198,879