US20060188268A1

US20060188268A1 - Optical drive for controlling output power of a pick-up head using apc loop

Info

Publication number: US20060188268A1
Application number: US11/381,539
Authority: US
Inventors: Hsueh-Kun Liao; Hseang-Ji Hsieh
Original assignee: MediaTek Inc
Current assignee: MediaTek Inc
Priority date: 2002-09-13
Filing date: 2006-05-04
Publication date: 2006-08-24
Also published as: US20040052184A1; TWI226625B; US7072273B2

Abstract

An optical drive includes a comparator for comparing a first input signal with a second input signal to generate a first output signal at a first node; a signal source coupled to a second node, the signal source outputting a second output signal; and a switch for outputting a third output signal at a third node, the third output signal controlling a laser power of the optical drive, wherein when the switch is switched to the first node, the first output signal is transmitted to the third node and serves as the third output signal, and when the switch is switched to the second node, the second output signal is transmitted to the third node and serves as the third output signal.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 10/249,221 entitled, “METHOD FOR CONTROLLING OUTPUT POWER OF A PICK-UP HEAD USING APC LOOP”, which was filed on Mar. 24, 2003 and is included herein by reference.

BACKGROUND

The present invention relates to an optical drive, more particularly, an optical drive for automatically controlling output power of a pick-up head of an optical drive with an APC loop.
In recent years, along with the increasing operating capability of the computer system combined with the development of Internet technology, users have widely made use of the computer system as the multi-media audiovisual medium and made use of the computer as a bridge for connecting with a network to access all kinds of information. Due to the increasing need of the data storage quantity, various tools and apparatuses for storing data immediately become popular. Since the optical disk has the advantages of compactness, large storage capacity, and inexpensiveness, related products became very attractive. Recently, the functions of the optical drive (such as a CD-RW drive) have increased, and the reading quality and access speed of the optical drive have been improved continuously. Moreover, in addition to the original specification of CD, the new specification of DVD appears with much larger capacity and the same physical volume with CD. Nowadays, the optical drive has become the standard equipments of the computer system.
The CD-RW drive access data according to the optical principles, therefore the reading and writing operations depend on a pick-up head, which is usually a laser head. During the reading process, the CD-RW drive will set the output power of the output laser of the pick-up head to a predetermined value to set the wavelength of the output laser to a constant value so that the wavelength of reflected light is equal to a value of a optical signal that a sensor of the CD-RW drive can detect. The optical disk stores the data by the way of pressing or recording some concaves, convexes, or special membranes with various optical characteristics on the surface of the optical disk so that the optical sensor can distinguish a plurality of different wavelengths of reflected light to store the data with the digital form. During the writing process, a CD-RW drive also will set the output power of the output laser of the pick-up head to a predetermined value to set the wavelength of the output laser to a constant value so that the pick-up head can identify the parameters of the membranes on the surface of the optical disk and control the laser to output a plurality of wavelengths continuously according to the digital data to be written onto the optical disk. Therefore, the digital data can be pressed and recorded onto the optical disk.
Please refer to FIG. 1. During the reading process and writing process, in order to make the CD-RW drive maintain the output power of the laser pick-up head at a predetermined value without fluctuating with the changes of the environment such as the temperature, the prior art usually makes use of an APC loop 10 in a CD-RW drive as shown in FIG. 1 to form a feedback closed loop with a pick-up head 20 for stabilizing the output power. The APC loop 10 comprises a drive circuit 18, a comparator circuit 14, a sensor 12, and a signal source 16. The drive circuit 18 is electrically connected to the pick-up head 20 for driving the pick-up head 20. The comparator circuit 14 comprises a first input port, a second input port, and an output port. The comparator circuit 14 compares two signals respectively transmitted from the first input port and the second input port to generate a corresponding comparative signal y. The output port is electrically connected to the drive circuit 18 for outputting the comparative signal y to the drive circuit 18. The sensor 12 is used to detect the output power of the pick-up head 20 to generate a corresponding detecting signal ε and to input the detecting signal E to the first inputs port of the comparator circuit 14. The signal source 16 is used to provide a signal γ to the second input port of the comparator circuit 14, and the signal γ represents the expected value of the output power of the pick-up head 20 of the CD-RW drive. The sensor 12 creates the signal ε which then feedbacks to the comparator circuit 14, and the APC loop 10 makes use of the comparator circuit 14 to compare the feed-backed signal ε with the signal γ representing the expected value of output power to generate the comparative signal y for controlling the output power of the pick-up head 20. Making use of the feedback control mechanism and designing the APC loop 10 with proper parameters can maintain the output power of the pick-up head 20 at an anticipant value. The user can insert various signal amplification circuits or power amplification circuits among the components of the APC loop 10 (such as inserting amplification circuits between the output port of the comparator circuit 14 and the drive circuit 18) according to practical needs. Moreover, the comparator circuit 14 can be achieved with various circuit configurations, and generally the comparator circuit 14 comprises an operational amplifier 22, a capacitor 24, and two resistors 26 and 28 that are connected as shown in FIG. 1. The signal source 16 usually is a digital signal-processing (DSP) chip for generating a digital signal that is transformed through a D/A converter.
However, the APC loop 10 has a very serious drawback when the output power of the pick-up head 20 is to be changed in the CD-RW drive. That is, the APC loop 10 needs to take a period of time to reach steady state. Please refer to FIG. 2. FIG. 2 is a schematic diagram showing how the signal γ, the comparative signal y, the detecting signal ε (as shown in FIG. 1), and the voltage drop Vc of the capacitor 24 vary with the time dimension t. Please notice that regarding the parameters of the components of the APC loop 10, when the signal γ is set as γ1 and the APC loop 10 reaches the steady state, the comparative signal y can be set as y1, the detecting signal ε can be set as γ1, and the voltage drop Vc is (γ1-y1). When the signal γ is γ2 and the APC loop 10 reaches the steady state, the comparative signal y is y2, the detecting signal ε is γ2, and the voltage drop Vc becomes (γ2-y2). When that CD-RW drive wants to raise the output power of the pick-up head 20 from a lower value to a higher value, the signal γ will be switched from γ1 to γ2 at time t1. At this time, the voltages of all nodes in the APC loop 10 will be shifted from original steady-state values to new steady-state values. However, due to the effect of capacitance in the APC loop 10 (such as the capacitor 24 that provides most of the effect of capacitance in the APC loop 10 as shown in FIG. 1), the new steady state will be reached after the effective capacitor is charged. As shown in FIG. 2, the voltage drop Vc is (γ1-y1) at time t1, and then at time t2 the voltage drop Vc enters a steady-state value (γ2-y2) after charging process. Similarly, the comparative signal y is y1+(γ2-γ1) at time t1, and at time t2 the comparative signal y reaches a steady-state value y2 after charging process. The detecting signal ε is γ2′ at time t1, and then enters a steady-state value γ2 at time t2. When that CD-RW drive wants to adjust the output power of the pick-up head 20 from a higher value to a lower value, the signal γ will be shifted from γ2 to γ1 at time t3. At this time, the voltages of all nodes in the APC loop 10 will be shifted from original steady-state values to new steady-state values. However, due to the effect of capacitance in the APC loop 10, the new steady state will be reached after the effective capacitor is discharged. As shown in FIG. 2, the voltage drop Vc is (γ2-y2) at time t3, and then enters a steady-state value (γ1-y1) at time t4 after discharging process. Similarly, the comparative signal y is y2-(γ2-γ1) at time t3, and then enter a steady-state value y1 at time t4 after discharging process. The detecting signal ε is γ1′ at time t3, and then reaches a steady-state value γ1 at time t4 after discharging process.
The above-mentioned effect of capacitance in the APC loop resulting from the charging/discharging process toward the effective capacitor will cause a period of time of unsteady state, and the unsteady state will do harm to the operations of the CD-RW drive. During the writing process, when the reading speed of a buffer is higher than the writing speed, the CD-RW drive must stop recording until the register enters the idle status. Because the long period of time of unsteady state leads to the destabilization of the output power, bug data are easily generated in the connecting point. During the reading process, the long period of time of unsteady state easily leads to the servo failure. For example, the tracking servo or the focusing servo may be out of control during the reading process.

SUMMARY

It is therefore an objective of the claimed invention to provide an optical drive to solve the above-mentioned problems of the prior art.
According an embodiment of the claimed invention, an optical drive is disclosed. The optical drive comprises: a comparator for comparing a first input signal with a second input signal to generate a first output signal at a first node; a signal source coupled to a second node, the signal source outputting a second output signal; and a switch for outputting a third output signal at a third node, the third output signal controlling a laser power of the optical drive, wherein when the switch is switched to the first node, the first output signal is transmitted to the third node and serves as the third output signal, and when the switch is switched to the second node, the second output signal is transmitted to the third node and serves as the third output signal.
According to another embodiment of the present invention, a circuit is disclosed. The circuit comprises: a comparator for comparing a first input signal with a second input signal to generate a first output signal at a first node; a first signal source coupled to a second node, for outputting a second output signal; a first switch coupled to a third node, wherein when the first switch is switched to the first node, the first output signal is transmitted to the third node, and when the first switch is switched to the second node, the second output signal is transmitted to the third node; and a switch controller for controlling the switching operation of the first switch in response to the first output signal and the second output signal.
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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an APC loop of the prior art.
FIG. 2 is a schematic diagram showing all signals in the APC loop as shown in FIG. 1 varying with time.
FIG. 3 is a functional block diagram of an APC loop of the present invention.
FIG. 4 is a schematic diagram showing all signals in the APC loop as shown in FIG. 3 varying with time.

DETAILED DESCRIPTION

Please refer to FIG. 3. FIG. 3 is a functional block diagram of an APC loop 30 of the present invention. The APC loop 30 comprises a sensor 32, a drive circuit 38, a comparator circuit 34, a first switch 54, a second switch 56, a first signal source 50, a switch controller 58, and a second signal source 36. The sensor 32 is used to detect output power of a pick-up head 40 to generate a corresponding detecting signal ε. The comparator circuit 34 comprises a first input port, a second input port, and an output port. The comparator circuit 34 is used to compare two signals inputted from the first input and the second input port to generate a corresponding comparative signal y, and the output port is used to output the comparative signal y. The first switch 54 is used to select either an output signal of a power supply 52 or the detecting signal ε of the sensor 32 to input the selected signal to the first input port of the comparator circuit 34. The first signal source 50 is used to provide a first signal. The drive circuit 38 is electrically connected to the pick-up head 40 for driving the pick-up head 40. The second switch 56 is used to select either the first signal or the comparative signal y′ to output the selected signal to the drive circuit 38. The second signal source 36 is used to provide a second signal y to the second input port of the comparator circuit 34, and the second signal γ represents the expected value of the output power of the pick-up head 40 in the CD-RW drive. The switch controller 58 is used to control the first switch 54 and the second switch 56 according to at least one node signal value in the APC loop 30. The user can insert various signal amplification circuits or power amplification circuits among the components of the APC loop 30 (such as inserting amplification circuits between the output port of the comparator circuit 34 and the drive circuit 38) according to practical needs. The sensor 32 is usually a photodiode for detecting the output power of the pick-up head 40. The comparator circuit 34 can be achieved with various circuit configurations, and generally the comparator circuit 34 comprises an operational amplifier 42, a capacitor 44, and two resistors 46 and 48 that are connected as shown in FIG. 1. The second signal source 36 usually is a digital signal-processing (DSP) chip for generating a digital signal that is transformed through a D/A converter. In addition, the power supply 52 can be a voltage source to provide a plurality of output voltage signals as shown in the following embodiment, and the power supply 52 also can be a current source to provide a plurality of output current signals. In an embodiment of the present invention, the first signal source 50 is generated by a set of comparative signals y according to the initial calibration process from a closed loop status to the steady state of the APC loop 30 in the CD-RW drive. The power supply comprises a system voltage Vcc and a voltage source 52 of a ground potential GND. The switch controller 58 controls the first switch 54 and the second switch 56 according to the comparative signal y of the comparator circuit 34 and the first signal. The operating principles are described as follows. When the second signal γ generates a step transition, the switch controller 58 will utilize the first switch 54 from the detecting signal ε to the voltage source 52, and utilize the second switch 56 from the signal y to the first signal. When number of times equals to two at which the comparative signal y is equivalent to the signal, the switch controller 58 will return the first switch 54 from the voltage source 52 to the detecting signal ε. At the same, the switch controller 58 will return the second switch 56 from the first signal to the signal y. The APC loop 30 of the present invention is described in detail in FIG. 4.
FIG. 4 is a schematic diagram showing how the second signal γ, the output signal χ of the first switch, the comparative signal y, the detecting signal ε, voltage drop Vc of the capacitor 44, and the output signal y′ of the second switch vary along with the time t. Please notice that regarding the parameters of the components of the APC loop 30, when the signal γ is set as γ1 and the APC loop 30 reaches the steady state, the comparative signal y can be set as y1, the detecting signal ε can be set as γ1 , and the voltage drop Vc is (γ1-y1). When the signal γ is γ2 and the APC loop 30 reaches the steady state, the comparative signal y is y2, the detecting signal ε is γ2, and the voltage drop Vc becomes (γ2-y2). When that CD-RW drive wants to raise the output power of the pick-up head 40 from a lower value to a higher value, the signal γ will be switched from γ1 to γ2 at time t1. At this time, if y>y′, the switch controller 58 will utilize the first switch 54 from the detecting signal ε to the system voltage Vcc of the voltage source 52 (as shown in FIG. 4, the output signal χ jumps to Vcc at time t1). Afterwards, the system voltage Vcc will quickly charge the capacitor 44 to make the voltage drop Vc from the value of (γ1-y1 ) at time t1 enter the steady-state value (γ2-y2) at time t2 in a very short time, and the switch controller 58 also will utilize the second switch 56 from the comparative signal y to the first signal. Since the first signal is generated through the initial calibration, the first signal is almost equal to the steady-state value y2 of the signal y. Hence the first signal can replace the comparative signal y to be inputted into the drive circuit 38 before the comparative signal y reaches the steady-state value y2 for generating an output power of the pick-up head 40 that approximates to the expected output power. After the comparative signal y reaches the steady-state value y2, the switch controller 58 utilizes those two switches and returns the APC loop 30 to a closed loop for providing stabilization of the output power. When the CD-RW drive wants to raise the output power of the pick-up head 20 from a higher value to a lower value, the signal γ will be switched from γ2 to γ1 at time t3. If y<y′, the switch controller 58 will utilize the first switch 54 from the detecting signal ε to the GROUND POTENTIAL GND of the voltage source 52 (as shown in FIG. 4, the output signal χ decreases to ground potential GND at time t3). Afterwards, the ground potential GND will quickly discharge the capacitor 44 to make the voltage drop Vc from the value of (γ2-y2) at time t3 enter the steady-state value (γ1-y1 ) at time t2 in a very short time, and the switch controller 58 also will utilize the second switch 56 from the comparative signal y to the first signal. Since the first signal is generated through the initial calibration, the first signal is almost equal to the steady-state value y1 of the signal y. Hence the first signal can replace the comparative signal y to be inputted into the drive circuit 38 before the comparative signal y reaches the steady-state value y2 for generating an output power of the pick-up head 40 that approximates to the expected output power. After the comparative signal y reaches the steady-state value y1, the switch controller 58 utilizes those two switches and returns the APC loop 30 to a closed loop for providing stabilization of the output power. Comparing the present invention as shown in FIG. 2 to the prior art as shown in FIG. 2, the capacitor 44 of the present invention has much shorter charging time (t2-t1) and the discharging time (t4-t3) than the charging time (t2-t1) and the discharging time (t4-t3) of the capacitor 24 in the prior art. That is, compared with the prior art, the comparative signal y of the present invention arrives at the steady state sooner since the present invention makes use of a relative large voltage drop to charge/discharge the capacitor 44. In addition, the output signal y of the second switch for controlling the output power of the pick-up head 40 is almost maintained to a steady-state value since the present invention makes use of the first signal that approximates to the steady-state value of the comparative signal y to replace the comparative signal y to be inputted into the drive circuit 38 before the comparative signal y reaches the steady-state value y2 for generating an output power of the pick-up head 40 that approximates to the expected output power. Therefore, the APC loop 30 of the present invention can quickly stabilize the output power of the pick-up head 40.
In contrast to the prior art, the method of the present invention makes use of a first switch to charge/discharge the effective capacitor of the APC loop and a second switch to provide a signal that approximates the steady-state value of the comparative signal to replace the comparative signal to be inputted into the drive circuit 38 for controlling the output power of the pick-up head. Therefore, the APC loop of the present invention can quickly stabilize the output power of the pick-up head. Moreover, in addition to the CD-RW drive, the APC loop of the present invention can also be applied to various rewritable optical drives, including DVD-RW, DVD+RW, DVD-RAM, and so on.
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. An optical drive, comprising:

a comparator for comparing a first input signal with a second input signal to generate a first output signal at a first node;

a signal source coupled to a second node, the signal source outputting a second output signal; and

a switch for outputting a third output signal at a third node, the third output signal controlling a laser power of the optical drive, wherein when the switch is switched to the first node, the first output signal is transmitted to the third node and serves as the third output signal, and when the switch is switched to the second node, the second output signal is transmitted to the third node and serves as the third output signal.

2. The optical drive of claim 1, further comprising:

a switch controller for controlling the switching operation of the switch in response to the first output signal and the second output signal.

3. A circuit, comprising:

a first signal source coupled to a second node, for outputting a second output signal;

a first switch coupled to a third node, wherein when the first switch is switched to the first node, the first output signal is transmitted to the third node, and when the first switch is switched to the second node, the second output signal is transmitted to the third node; and

a switch controller for controlling the switching operation of the first switch in response to the first output signal and the second output signal.

4. The circuit of claim 3, further comprising:

a power supply for outputting a first reference signal at a fourth node and a second reference signal at a fifth node;

a second signal source for outputting the second input signal to the comparator, wherein a value of the first reference signal is greater than that of the second input signal, and a value of the second reference signal is less than that of the second input signal; and

a second switch coupled to a sixth node, the first input signal being communicated to the comparator thorough the sixth node, wherein when the second switch is switched to the fourth node, the fourth node is connected to the sixth node, and when the second switch is switched to the fifth node, the fifth node is connected to the sixth node.

5. A circuit, comprising:

a comparator comprising a first input and a second input;

a power supply for outputting a first reference signal at a first node and a second reference signal at a second node;

a first signal source for outputting a first output signal to the second input of the comparator, wherein a value of the first reference signal is greater than that of the first output signal, and a value of the second reference signal is less than that of the first output signal; and

a first switch coupled to a third node, the third node being coupled to the first input of the comparator, wherein when the first switch is switched to the first node, the first node is connected to the third node, and when the first switch is switched to the second node, the second node is connected to the third node.

6. The circuit of claim 5, wherein the first reference signal is a voltage signal and the second reference signal is a voltage signal.

7. The circuit of claim 5, wherein the first reference signal is a current signal and the second reference signal is a current signal.

8. The circuit of claim 5, wherein the comparator compares a first input signal from the first input with a second input signal from the second input to generate a second output signal at a fourth node, the circuit further comprising:

a second signal source for outputting a third output signal at a fifth node; and

a second switch for outputting a fourth output signal at a sixth node, wherein when the second switch is switched to the forth node, the second output signal is transmitted to the sixth node and serves as the fourth output signal, and when the second switch is switched to the fifth node, the third output signal is transmitted to the sixth node and serves as the fourth output signal.