Patent Application
20060077823
The invention generally relates to optical recording and storage drives, and more particularly, to a system and a method for automatically calibrating the proper output power of a light emitting device.
As requirements for high volume storage mediums continue to increase, optical discs (for example, CDs and DVDs) are playing a more important role. During the manufacturing process, pits are created on the optical discs by an optical pickup unit (OPU) of the optical disc recorder by emitting a light beam on the optical disc. Lands are formed on the optical disc when no light beam is emitted thereon. Pits have a lower reflectivity than the lands, and each pit and each land represent information of 0 and 1, respectively.
However, pits produced by laser beams of different output power levels from different optical disc recorders are usually shaped differently, which causes difficulty in the process of reproducing the recorded information. This is a result of the variation in the assembly of the OPU and inconsistencies in the photo diode properties. Therefore, the optical disc recorder has to have its laser power calibrated prior to the fab-out stage so that the OPU can provide laser beams of the correct power.
Although not shown, the power calibration system 100 requires the application of a standard photo diode to be used with the power calibration system, in addition to requiring control to be performed by the computer 112. These requirements significantly increase the manufacture costs. Additionally, in order to command the laser diode 102 of the optical recording drive 104 to progressively emit light beams of increasing power levels, the optical recording drive 104 must be equipped with some kind of a digital port to receive the commands from the computer 112. In PC related applications (for example, CD-R/RW drive, DVD-R/RW drive, DVD+R/RW drive, . . . etc.), an ATAPI interface is typically used for this purpose. However, in order to reduce costs, in consumer electronic applications, the optical disc recorders (for example, CD-R/RW recorder, DVD recorder, . . . etc) are generally not equipped with ATAPI interfaces because such interfaces are not needed during normal operations. Therefore an improved light emitting device calibration method for the laser diode of optical disc drives, optical disc recorders, and other products having light emitting devices is required.
One objective of the invention is therefore to provide a method for automatic calibration of a light emitting device not requiring external test equipment or an external computer to thereby solve the above-mentioned problems.
According to an exemplary embodiment of the invention, a method is disclosed for automatic light emitting device calibration comprising the following steps: providing an optical device having a light emitting device and a photo monitor; controlling power of the light emitting device by changing values of a drive signal to the light emitting device; detecting light emitted by the light emitting device and generating a monitor signal having a value corresponding to the light emitted by the light emitting device utilizing the photo monitor; and determining a preliminary power relationship relating values of the drive signal to powers of the light emitting device according to received monitor signal values for a plurality of drive signal values and a predetermined conversion rule for converting the received monitor signal values to corresponding powers of the light emitting device.
According to another exemplary embodiment of the invention, an auto-calibrating optical device is disclosed comprising: a light emitting device to be calibrated; a photo monitor for detecting light emitted by the light emitting device and generating a monitor signal having a value corresponding to the light emitted by the light emitting device; and a microprocessor coupled to the light emitting device and the photo monitor for controlling power of the light emitting device by changing values of a drive signal to the light emitting device; and for during a calibration mode, determining a preliminary power relationship relating values of the drive signal to powers of the light emitting device according to received monitor signal values for a plurality of drive signal values and a predetermined conversion rule for converting the received monitor signal values to corresponding powers of the light emitting device.
These and other objectives of the 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.
After assembly at the manufacturer, the optical drive 200 performs automatic calibration of the laser power of the LD 211. Power is applied to the optical device 200 and the microprocessor 202 enters a calibration mode. For example, a jumper in the device under test 200 could be set to control the microprocessor 202 to enter the calibration mode, or other methods such as temporally loading program code corresponding to the calibration mode into the EEPROM 204 for execution by the microprocessor 202 at power-on. Once in the calibration mode, the microprocessor 202 controls the output power of the LD 210 by changing values of the drive signal DS to the pickup module 208. A plurality of different values of the drive signal DS are outputted by the microprocessor 202. The pre-amplifier IC 206 drives the pickup module to control the LD 210 at different output power levels corresponding to the different values of the drive signal DS. Light emitted by the LD 210 is sensed by the FMD 212 and the monitor signal MS corresponding to the front monitor signal VFMD is passed to the microprocessor 202. The microprocessor 202 then utilizes a predetermined conversion rule for converting the received monitor signal MS values to corresponding powers of the LD 210, and thereby determines a preliminary power relationship relating values of the drive signal DS to powers of the light emitted by the LD 210.
In this embodiment, the microprocessor 202 progressively increases the values of the drive signal DS; however, the present invention is not limited to only this embodiment. For example, if the slope of the second portion 402 of the power curve is assumed to be linear, calibration of the LD 210 can be performed using only two values (e.g., DS1 and DS2) of the drive signal DS. More specifically, the microprocessor 202 controls the power of the LD 210 by utilizing a first drive signal value DS1 and a second drive signal value DS2. A first monitor signal value is received corresponding to the first drive signal value DS1, and a second monitor signal value is received according to the second drive signal value DS2. The microprocessor 202 then extrapolates monitor signal values in a line formed between the first received monitor signal value and the second received monitor signal value. In order to determine the offset value DS0 of the drive signal, the microprocessor 202 determines a crossing value of the drive signal corresponding to where the extrapolated monitor signal values of the line cross the predetermined value A of the monitor signal when the LD 210 is not emitting any light. Finally, the microprocessor 202 converts the extrapolated monitor signal MS values of the line corresponding to drive signal DS values being higher than the offset value DS0 to power values according to the predetermined conversion rule to thereby generate the preliminary power relationship.
At this point, the preliminary power relationship determined by the microprocessor 202 is sufficiently accurate to be used to control the read power of the LD 210. However, there is a uncertainty (for example, approximately 10% value variation) between particular front monitor signals VFMD of different FMDs 212 of different optical drives 200. Because the write laser power of the LD 210 is desired to be controlled precisely in order to ensure accurate pit creation during the recording phase of an optical disc, in a preferred embodiment of the present invention, the preliminary power relationship is further corrected using a power relationship correction operation. The power relationship correction operation is performed on an optical disc of the optical device 200 during the automatic calibration process at the manufacture. During the automatic calibration process, the microprocessor 202 controls the optical drive 200 to write test data to an optical disc of the optical device 202 using a particular drive signal DS value for a predetermined power value. The preliminary power relationship (
There are various implantations of the power relationship correction operation. One example is the Optimum Power Control (OPC) process commonly performed by optical disc drives of the related art before recording information on an optical disc. Because different optical discs have different optimal laser write power requirements, the OPC process is used by the related art optical devices to optimize the write power of the laser diode according to a specified optimal power requirement for particular optical disc. Typically, the OPC process is performed by the related art optical devices in an OPC section of the optimal disc. The OPC section must be used because the OPC process involves writing test data to the optical disc that if not written in the OPC section, would interfere with user data stored on the optical disc. As the OPC process is well known to a person of ordinary skill in the art, further description of the specific operations of the OPC process is omitted herein. However, it should also be noted that in this embodiment, because the present invention uses the OPC process as the power relationship correction operation that is performed at the manufacturer, there is no concern with interfering with user data stored on the optical disc. Therefore, the power relationship correction operation can be a modified OPC process being performed in any section of the optical disc.
The final power relationship is then stored in the non-volatile memory EEPROM 204 and automatic calibration is completed. During normal operations, the final power relationship stored in the EEPROM 204 is used for controlling values of the drive signal DS according to desired powers of the light emitting device. For example, the final power relationship can be used to provide a starting value for the OPC process for writing operations to different optical discs. Because the final power relationship is optimized for the particular FMD 212 of the optical drive 200, the OPC process for recording operations performed during normal user mode operations could be completed much faster.
Step 700: Provide an optical device having a light emitting device and a photo monitor.
Step 702: Control the power of the light emitting device by changing values of a drive signal to the light emitting device.
Step 704: Detect light emitted by the light emitting device and generate a monitor signal having a value corresponding to the light emitted by the light emitting device utilizing the photo monitor.
Step 706: Determine a preliminary power relationship relating values of the drive signal to powers of the light emitting device according to received monitor signal values for a plurality of drive signal values and a predetermined conversion rule for converting the received monitor signal values to corresponding powers of the light emitting device. The preliminary power relationship is sufficiently accurate to be used to control the read power of the light emitting device. However, because the write laser power of the light emitting device is preferred be controlled precisely in order to ensure an accurate recording phase, in a preferred embodiment of the present invention, the preliminary power relationship is further corrected using a power relationship correction operation at step 708.
Step 708: Generate a final power relationship by performing a power relationship correction operation on an optical medium of the optical device. The power relationship correction operation includes steps 710-714. One or more iterations of the power relationship correction operation (step 708) could be performed to thereby obtain a final power relationship having an accurate drive signal to LD 210 power values for the particular FMD 212.
Step 710: Write test data to the optical medium of the optical device using a particular drive signal value for a predetermined power value according to the preliminary power relationship.
Step 712: Read a read signal corresponding to the test data from the optical medium.
Step 714: Analyze the read signal to determine if the test data was written to the optical medium at the particular power and correspondingly adjust the preliminary power relationship such that the test data is written to the optical medium at the predetermined power to thereby generate the final power relationship.
Step 716: Store the final power relationship in a non-volatile memory of the optical device to complete the automatic light emitting device calibration. During normal operations, control values of the drive signal to control the power of the light emitting device according to the final power relationship stored in the non-volatile memory.
The present invention provides an auto-calibrating optical device and associated method of automatic light emitting device calibration that does not require control from an external computer, an expensive power meter, or any other external test equipment. Manufacturing costs are therefore greatly reduced. Additionally, because the calibration process is controlled by a microprocessor embedded in the auto-calibrating optical device, the calibration process is simplified and easily automated. Furthermore, as the optical device performs automatic calibration without receiving signals from outside the optical device, no interface port needs to be installed on the optical device. The present invention is therefore well suited for use with both PC-related optical drives (such as CD-R/RW drives, DVD-R/RW drives, DVD+R/RW drives . . . , etc.) and consumer electronic optical devices (such as CD-R/RW recorders, DVD recorders, . . . etc.) having no external interface port.
Those skilled in the art will readily observe that numerous modifications and alterations of the device 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.
