Offset calibration system and method of automatic power control loop

An offset calibration system of a control loop at least comprises an optical-to-electrical converter and an electrical-to-optical converter. The optical-to-electrical converter generates a pre-output signal and then transmits the pre-output signal to the electrical-to-optical converter to amplify. The offset calibration system comprises a comparator, an offset calibration module, and a determination circuit. The comparator compares the pre-output signal with a predetermined pre-reference signal to generate a pre-compared signal. The offset calibration module stores a predetermined and adjustable offset calibration value for adding to the pre-output signal. The determination circuit adjusts the offset calibration value based on the pre-compared signal, so the offset calibration value can be added to the pre-output signal dynamically to compensate and calibrate the offset of the pre-output signal caused by the optical-to-electrical converter to avoid the electrical-to-optical converter amplifying the offset of the pre-output signal again.

FIELD OF THE INVENTION

The present invention relates to an offset calibration system and method of an automatic power control loop for calibrating the offset generated by the automatic power control loop.

BACKGROUND OF THE INVENTION

When the pickup head of an optical information recording/reading apparatus writes and reads pits of a compact disk, an automatic power control loop is used to control and adjust the laser power of the laser diode within the pickup head. A pickup head comprises a laser diode, a laser diode driver and a laser power detector. The laser diode provides a laser source to read or write data on the compact disk. The laser power detector detects the laser power of the laser beam reflecting from the compact disk to output a corresponding laser power detection signal.

The pickup head uses different laser powers when it is writing or reading. The power in writing is higher than the power in reading. The laser powers are also different depending on writing/reading a land storage track or a groove storage track. It is important to control the power of the laser emitted by the laser diode. The laser diode is driven by the laser diode driver. Hence, controlling the laser diode driver can further control the laser power.

The automatic power control loop controls the laser diode driver to output a electric current to drive the laser diode for emitting a laser bean with an adequate laser power.

The laser power detection signal outputted by the laser power detector and the laser power of the detected laser beam are in inverse proportion. The laser power detection signal will be sampled and held by a sample/hold circuit of the automatic power control loop, and then transmitted to a pre-amplifier for amplifying to generate a pre-output signal. The pre-output signal is subtracted by a predetermined reference signal in an adder. If the result value does not equal to zero, the laser power of the laser beam still needs to be adjusted. A post-amplifier can adjust the pre-output signal and generate a power control signal. The post-amplifier transmits the power control signal to the laser diode driver for emitting an adequate laser power. In an ideal condition, when the laser diode doesn't emit the laser beam, the pre-output signal is the predetermined reference signal.

In general, the prior art control and calibration method for the laser power emitted by the laser diode can adjust the laser power very well. However, in the prior art, when the laser power detector generates a laser power detection signal with an offset, the automatic power control loop can't calibrate immediately. Through the amplifier, the offset is amplified and may be beyond the range that the adder can adjust. Therefore, a wrong power control signal is produced resulting in a wrong laser power wrong. Consequently, mistakes occur in writing/reading data of the compact.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present invention to provide an offset calibration system and method of an automatic power control loop for calibrating a laser power emitted from a laser diode so that the laser diode can emit accurate laser power.

The automatic power control loop of the present invention comprises a pre-amplifier circuit and a post-amplifier circuit. The pre-amplifier circuit generates a pre-output signal and then transmits the pre-output signal to the post-amplifier circuit for amplifying. The offset calibration system comprises a competitor, an offset calibration module and a determination circuit. The competitor compares the pre-output signal with a predetermined pre-reference signal to generate a pre-compared signal. The offset calibration module stores a predetermined and adjustable offset calibration value for adding to the pre-output signal. The determination circuit electrically connects to the competitor and the offset calibration module to adjust the offset calibration value stored in the offset calibration module based on the pre-compared signal generated by the competitor.

The determination circuit adjusts the offset calibration value dynamically based on the pre-compared signal, so the offset calibration value can be added to the pre-output signal dynamically to compensate and calibrate the offset of the pre-output signal caused by the pre-amplifier circuit. That will avoid the post-amplifier circuit amplifies the offset of the pre-output signal again.

The present invention calibrates the offset of an automatic power control loop by the offset calibration system. The offset of the pre-output signal can be compensated and calibrated immediately by the offset calibration system of the present invention to avoid that the post-amplifier circuit amplifies the offset of the pre-output signal again.

As another embodiment, the automatic power control loop of the present invention comprises an optical-to-electrical converter and an electrical-to-optical converter. The optical-to-electrical converter receives an optical input signal, generates a pre-output signal and then transmits the pre-output signal to the electrical-to-optical converter for amplifying the pre-output signal and then generating an optical output signal. The offset calibration system comprises a comparator, an offset calibration module and a determination circuit. The comparator compares the pre-output signal with a predetermined pre-reference signal to generate a pre-compared signal. The offset calibration module stores a predetermined and adjustable offset calibration value for adding to the pre-output signal. The determination circuit electrically connects to the comparator and the offset calibration module to adjust the offset calibration value stored in the offset calibration module based on the pre-compared signal generated by the comparator.

The determination circuit adjusts the offset calibration value dynamically based on the pre-compared signal, so the offset calibration value can be added to the pre-output signal dynamically to compensate and calibrate the offset of the pre-output signal caused by the optical-to-electrical converter. That will avoid the electrical-to-optical converter amplifies the offset of the pre-output signal again.

The present invention calibrates the offset of an automatic power control loop by the offset calibration system. The offset of the pre-output signal can be compensated and calibrated immediately by the offset calibration system of the present invention to avoid that the electrical-to-optical converter amplifies the offset of the pre-output signal again.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.

DETAILED DESCRIPTION OF THE INVENTION

Please refer toFIG. 1.FIG. 1is a block diagram of an offset calibration system20of an automatic power control system1according to the present invention. The present invention is an offset calibration system20of a control loop1. The control loop1comprises a pre-amplifier circuit10and a post-amplifier circuit11. The pre-amplifier circuit10generates a pre-output signal S1and then transmits the pre-output signal S1to the post-amplifier circuit11to amplify. The control loop1is an automatic power control loop to control a laser source device30.

The laser source device30comprises a laser diode32and a laser diode driver31. The automatic power control loop1controls the laser diode driver31to output a driving electric current to drive a compact disk system (not show inFIG. 1) with the laser beam when the compact disk system reads or writes a compact disk. The compact disk system comprises a pickup head which comprises a laser power detector to detect a laser power of the laser beam reflecting from the compact disk, and to ouput a corresponding laser power detection signal. The laser power detection signal and the detected laser power of the laser beam are in inverse proportion.

The offset calibration system20of the present invention comprises a competitor22, an offset calibration module24, a determination circuit26, and a pre-adder28. A competitor22compares the pre-output signal S1with a predetermined pre-reference signal Sref to generate a pre-compared signal S2. The offset calibration module24stores a predetermined and adjustable analog offset calibration value AOC for adding to the pre-output signal S1. The determination circuit26electrically connects to the competitor22and the offset calibration module24to adjust the analog offset calibration value AOC stored in the offset calibration module24based on the pre-compared signal S2generated by the competitor22. The pre-adder28makes the analog offset calibration value AOC add to the pre-output signal S1to become a calibrated pre-output signal SC, and then transmits the calibrated pre-output signal SC to the post-amplifier circuit11.

The determination circuit26adjusts the analog offset calibration value AOC dynamically based on the pre-compared signal S2, so the analog offset calibration value AOC can be added to the pre-output signal S1dynamically to compensate and calibrate the offset of the pre-output signal S1caused by the pre-amplifier circuit10to avoid that the post-amplifier circuit11amplifies the offset of the pre-output signal S1again.

The offset calibration module24comprises a pre-register241and a pre-D/A converter242. The pre-register241stores a digital offset calibration value DOC. The pre-D/A converter242converts the digital offset calibration value DOC to a corresponding analog offset calibration value AOC. The analog offset calibration value AOC will be sent to the pre-adder28, and then added to the pre-output signal S1.

In an ideal situation, when the laser diode32doesn't emit the laser beam, the pre-output signal S1generated by the pre-amplifier circuit10is the predetermined pre-reference signal Sref. Only when the laser diode32doesn't emit the laser beam, the determination circuit26will adjust the offset calibration value based on the pre-compared signal S2to make the pre-adder28add the analog-offset calibration value AOC to the pre-output signal S1for compensating and calibrating.

Please refer toFIG. 2.FIG. 2is a block diagram of the pre-amplifier circuit10and the post-amplifier circuit11shown inFIG. 1. The pre-amplifier10comprises a sample/hold circuit12and a pre-amplifier14. The sample/hold circuit12samples and holds the laser power detection signal according to a control signal, and outputs a sample/hold signal S/h. The pre-amplifier14receives and amplifies the sample/hold signal S/h outputted from the sample/hold circuit12to generate the pre-output signal S1. The pre-output signal S1then is inputted to the offset calibration system20of the present invention for calibrating the offset.

As shown inFIG. 2, the calibrated pre-output signal SC is inputted to the post-amplifier circuit11. The post-amplifier circuit11provides a power control signal SP to control a laser diode driver31of the laser source device30. The post-amplifier circuit11, comprises a post-register13, a post-D/A converter15, a post-subtractor17, and a post-amplifier19. The post-register13stores a digital power adjustment value. The post-register13comprises a plurality of storage units to store the digital power adjustment value, and the number of storage units in the post-register13determines the range of the digital power adjustment value. The determination circuit26adjusts the offset calibration value according to the pre-compared signal S2to make the analog offset calibration value AOC added to the pre-output signal S1to avoid the pre-output signal S1being beyond the range of the power adjustment value in the post-register13.

The post-D/A converter15converts the digital power adjustment value to a corresponding analog power adjustment value. The post-subtractor17adds the analog power adjustment value to the calibrated pre-output signal SC to become a post-output signal S3. The post-amplifier19receives and amplifies the signal from the post-subtractor17to generate the power control signal SP. The power control signal SP can control the laser diode driver31, and further control the laser power of the laser beam emitted from the laser diode32.

Please refer toFIG. 3.FIG. 3is a flow chart of the automatic power control loop1and the offset calibration system20of the present invention according toFIG. 1andFIG. 2. The method comprises the following steps:Step S31: sampling and holding a laser power detection signal according to a control signal, and outputting a sample/hold signal S/h;

Step S32: amplifying the sample/hold signal S/h to generate a pre-output signal S1;

Step S33: storing a digital offset calibration value DOC;

Step S34: comparing the pre-output signal S1with a predetermined reference signal Sref to generate a pre-compared signal S2;

Step S35: dynamically adjusting the digital offset calibration value DOC according to the pre-compared signal S2;

Step S36: converting the digital offset calibration value DOC to a corresponding analog offset calibration value AOC,

Step S37: dynamically adding the analog offset calibration value AOC to the pre-output signal S1to become the calibrated pre-output signal SC to compensate and calibrate the offset of the pre-output signal caused by the pre-amplifier circuit to avoid the post-amplifier circuit amplifying the offset of the pre-output signal again,

Step S38: storing a power adjustment value in a digital way;

Step S39: converting the digital, power adjustment value to a corresponding analog power adjustment value;

Step S40: adding the analog power adjustment value to the calibrated pre-output signal SC to become a post-output signal S3;

Step S41: receiving and amplifying the post-output signal S3to generate a power control signal SP.

The following is the second embodiment of this invention. Please refer toFIG. 4.FIG. 4is a block diagram of an offset calibration system20of an automatic power control system1according to second embodiment of the present invention. The present invention is an offset calibration system20of a control loop1. As an embodiment, the control loop1comprises an optical-to-electrical converter10and an electrical-to-optical converter40. The optical-to-electrical converter10generates a pre-output signal S1and then transmits the pre-output signal S1to the electrical-to-optical converter40. The control loop1comprises a laser source device30and outputs a laser beam

The laser source device30comprises a laser diode32and a laser diode driver31. The automatic power control loop1outputs the laser beam to the compact disk system, and the driving electric current generated by the laser diode driver31controls the amplitude of the laser beam. The compact disk system comprises a pickup head which comprises a laser power detector to detect a laser power of the laser beam and to output a corresponding laser power detection signal.

The offset calibration system20of the present invention comprises a comparator22, an offset calibration module24, a determination circuit26, and a pre-adder28. The comparator22compares an added pre-output signal S1′ with a predetermined pre-reference signal Sref to generate a pre-compared signal S2. The offset calibration module24stores a predetermined and adjustable analog offset calibration value AOC for adding to a pre-output signal S1. The determination circuit26electrically connects to the comparator22and the offset calibration module24to adjust the analog offset calibration value AOC stored in the offset calibration module24based on the pre-compared signal S2generated by the comparator22. The pre-adder28makes the analog offset calibration value AOC added to the pre-output signal S1to become a calibrated pre-output signal SC, and then transmits the calibrated pre-output signal SC to the electrical-to-optical converter40.

The determination circuit26adjusts the analog offset calibration value AOC dynamically based on the pre-compared signal S2, so the analog offset calibration value AOC can be added to the pre-output signal S1dynamnically to compensate and calibrate the offset of the pre-output signal S1caused by the optical-to-electrical converter10to avoid that the electrical-to-optical converter11amplifies the offset of the pre-output signal S1again.

The offset calibration module24comprises a pre-register241and a pre-D/A converter242. The pre-register241stores a digital offset calibration value DOC. The pre-D/A converter242converts the digital offset calibration value DOC to a corresponding analog offset calibration value AOC. The analog offset calibration value AOC will be sent to the pre-adder28.

In an ideal situation, when the laser diode32doesn't emit the laser beam, the pre-output signal S1generated by the optical-to-electrical converter10is the predetermined pre-reference signal Sref. Only when the laser diode32doesn't emit the laser beam, the determination circuit26will adjust the offset calibration value based on the pre-compared signal S2to modify the analog offset calibration value AOC. When the laser diode32doesn't emit the laser beam, the analog offset calibration value AOC is initially set as zero and the initial added pre-output signal S1′ the same as pre-output signal S1. If the added pre-output signal S1′ is lower than the predetermined pre-reference signal Sref, the pre-compared signal S2will be set as zero. Accordingly, the determination circuit26will decrease the analog offset calibration value AOC to reduce the added pre-output signal S1′. If the added pre-output signal S1′ is still lower than the predetermined pre-reference signal Srcf, the pre-compared signal S2still will be zero and the determination circuit26will decrease the analog offset calibration value AOC to reduce the added pre-output signal S1′ again until the added pre-output signal S1′ is higher than the predetermined pre-reference signal Sref. At that moment, the determination, circuit26stop working and the analog offset calibration value AOC is fixed.

Please refer toFIG. 5.FIG. 5is a block diagram of the optical-to-electrical converter10and the electrical-to-optical converter40shown inFIG. 4. The pre-amplifier10comprises a sample/hold circuit12and a pre-amplifier14. The sample/hold circuit12samples and holds the laser power detection signal according to a control signal, and outputs a sample/hold signal S/h. The pre-amplifier14receives and amplifies the sample/hold signal S/h outputted from the sample/hold circuit12to generate the pre-output signal S1. The pre-output signal S1then is inputted to the offset calibration system20of the present invention for calibrating the offset.

As shown inFIG. 5, the calibrated pre-output signal SC is inputted to the electrical-to-optical converter40. The electrical-to-optical converter40comprises a post-amplifier circuit11and a laser source device30. The post amplifier circuit11provides a power control signal SP to control a laser diode driver31of the laser source device30. The post-amplifier circuit11comprises a post-register13, a post-D/A converter15, a post-subtractor17, and a post-amplifier19. The post-register13stores a digital power adjustment value. The post-register13comprises a plurality of storage units to store the digital power adjustment value, and the number of storage units in the post-register13determines the range of the digital power adjustment value. The determination circuit26adjusts the offset calibration value according to the pre-compared signal S2to make the analog offset calibration value AOC added to the pre-output signal S1to avoid the pre-output signal S1being beyond the range of the power adjustment value in the post-register13.

The post-D/A converter15converts the digital power adjustment value to a corresponding analog power adjustment value. The post-subtractor17adds the analog power adjustment value to the calibrated pre-output signal SC to become a post-output signal S3. The post-amplifier19receives and amplifies the signal from the post-subtractor17to generate the power control signal SP. The power control signal SP can control the laser diode driver31, and further control the laser power of the laser beam emitted from the laser diode32.

Please refer toFIG. 6.FIG. 6is a flow chart of the automatic power control loop1and the offset calibration system20of the present invention according toFIG. 4andFIG. 5. The method comprises the following steps:

Step S31: sampling and holding a laser power detection signal according to a control signal, and outputting a sample/hold signal S/h;

Step S32: amplifying the sample/hold signal S/h to generate a pre-output signal S1;

Step S33: Sotring a digital offset calibration value DOC and converting the digital offset calibration value DOC to a corresponding analog offset calibration value AOC;

Step S34: Generating an added pre-output signal S1′ by adding S1with a corresponding analog offset calibration value AOC;

Step S35: comparing the added pre-output signal S1′ with a predetermined reference signal Sref to generate a pre-compared signal S2;

Step S36: dynamically adjusting the digital offset calibration value DOC according to the pre-compared signal S2;

Step S37: dynamically converting the digital offset calibration value DOC to a corresponding analog offset calibration value AOC;

Step S38: Repeating from step S34to step S37until the added pre-output signal S1′ is substantially the same as the predetermined reference signal Sref by checking the change of the pre-compared signal S2.

Step S39: Adding the analog offset calibration value AOC to the pre-output signal S1to become the calibrated pre-output signal SC to compensate and calibrate the offset of the pre-output signal caused by the optical-to-electrical converter;

Step S40: storing a power adjustment value in a digital way,

Step S41: converting the digital power adjustment value to a corresponding analog power adjustment value;

Step542: adding the analog power adjustment value to the calibrated pre-output signal SC to become a post-output signal S3;

Step S43; receiving and amplifying the post-output signal S3to generate a power control signal SP.

Step S44: generating the laser beam by controlling the laser source device according to the power control signal SP.

The present invention utilizes an offset calibration system to compare and calibrate the pre-output signal generated by the pre-amplifier circuit. The invention makes the offset of the pre-output signal calibrated by the offset calibration system before outputted into the post-amplifier circuit to avoid the pre-output signal with offset to be transmitted to the post-amplifier circuit, so to avoid the offset being beyond the range of the power adjustment value. After amplifying, the offset will become the larger power control signal. However, the offset of the pre-output signal has been calibrated by the offset calibration system of the present invention, so that mistakes will not occur when writing/reading data of the compact disk system. This appears the advantage and the utility of the offset calibration system in the present invention. Also, the present invention utilizes an offset calibration system to compare and calibrate the pre-output signal generated by the optical-to-electrical converter. The invention makes the offset of the pre-output signal calibrated by the offset calibration system before outputted into the electrical-to-optical converter to avoid the pre-output signal with offset to be transmitted to the electrical-to-optical converter, so to avoid the offset being beyond the range of the power adjustment value. After amplifying, the offset will become the larger power control signal. However, the offset of the pre-output signal has been calibrated by the offset calibration system of the present invention, so that mistakes will not occur when writing/reading data of the compact disk system. This appears the advantage and the utility of the offset calibration system in the present invention.

The description of the above-mentioned preferred embodiments provides a better understanding on the strengths and spirits of this present invention, not to limit the domain of the invention. Moreover, it aims to include various modification and arrangement parallel in form into the domain of the patent applied by this present invention. Due to the above mention, the domain of the patent applied by the invention should be explained in a macro view to cover all kinds of possible modification and arrangement of equal form.