Optical pickup apparatus, integrated circuit, and method for controlling laser output of optical pickup apparatus

This application claims the benefit of priority to Japanese Patent Application No. 2011-060162, filed Mar. 18, 2011, of which full contents are incorporated herein by reference.

1. Field of the Invention

The present invention relates to an optical pickup apparatus, an integrated circuit, and a method for controlling laser output of an optical pickup apparatus.

2. Description of the Related Art

An optical pickup apparatus, configured to perform recording and reproducing signals for an optical disc, detects a laser beam emitted from a laser diode with a photodetector such as a photodiode, thereby controlling the output of the laser diode according to the intensity of the detected laser beam.

For example, Japanese Laid-Open Patent Publication No. 2003-132581 discloses, in FIG. 5, a back monitor type optical pickup apparatus configured to detect a laser beam emitted backward (which is not a direction of an optical disc) from a laser diode with a photodetector (back monitor photodetector) provided within the same package as that provided with the laser diode thereby controlling the drive current of the laser diode. For example, Japanese Laid-Open Patent Publication No. 2003-132581discloses, in FIG. 4, a front monitor type optical pickup apparatus configured to detect a laser beam emitted forward (which is a direction of an optical disc) from a laser diode with a photodetector (front monitor photodetector) other than the back monitor photodetector thereby controlling the drive current of the laser diode.

FIGS. 3 and 4 respectively depict examples of configurations of typical laser output control circuits in the back monitor type optical pickup apparatus and the front monitor type optical pickup apparatus.

As depicted in FIG. 3 , a back monitor photodiode (photodetector) PD 1 receives a laser beam emitted backward from a laser diode LD 1 , and a current Ibm according to the intensity of the received laser beam flows through the photodiode PD 1 . Further, the current Ibm flows through a variable resistor VR adjusted depending on an optical disc, and a voltage Vbm generated across the variable resistor VR is converted into a digital signal by an ADC (analog-digital converter: analog-digital converter circuit) 12 , and then inputted to an LD drive circuit 13 . The LD drive circuit 13 controls a drive current Ild 1 supplied from a power source 14 according to the voltage Vbm thereby controlling the output of the laser diode LD 1 .

Whereas, as depicted in FIG. 4 , a front monitor photodiode PDfm receives a laser beam emitted forward from a laser diode LD 2 , and a current Ifm according to the intensity of the received laser beam flows through the photodiode PDfm. Further, the current Ifm is converted into a voltage signal Vfm by an IV amplifier (current/voltage converter circuit) 44 , further converted into a digital signal by an ADC 22 , and then inputted to an LD drive circuit 23 . The LD drive circuit 23 controls a drive current Ild 2 supplied from a power source 24 according to the voltage Vfm thereby controlling the output of the laser diode LD 2 . The IV amplifier 44 includes a plurality of resistors for selecting a gain and a switch circuit (not depicted) configured to switch a resistor to be connected, and the gain can be adjusted by inputting a selection signal SEL in accordance with an optical disc from a controller 50 .

As such, the laser beam emitted from the laser diode is detected by the back monitor photodetector or the front monitor photodetector, thereby being able to control the output of the laser diode.

In the back monitor type laser output control circuit depicted in FIG. 3 , the current Ibm, flowing through the photodiode PD 1 provided within the same package as that provided with the laser diode LD 1 , is converted into the voltage Vbm using the variable resistor VR, to be used as a monitor signal indicative of the intensity of the laser beam. Therefore, the back monitor type enables inexpensive configuration of the laser output control circuit, and is mainly employed in an optical pickup apparatus configured to perform only reproducing operation.

On the other hand, in the front monitor type laser output control circuit depicted in FIG. 4 , the current Ibm, flowing through the photodiode PDfm other than the photodiode PD 2 , is converted into the voltage Vfm using the IV amplifier 44 , to be used as a monitor signal. The front monitor type enables faster response than that in the case of the back monitor type, and is therefore mainly employed in an optical pickup apparatus performs not only reproducing operation but also recording operation that requires high-speed control of the output of the laser diode.

By way of example, in an optical pickup apparatus that performs both recording and reproduction for CD (compact disc) and DVD (digital versatile disc) and performs only reproduction for BD (Blu-ray disc), a laser output control circuit for CD/DVD can be of the front monitor type and a laser output control circuit for BD can be of the back monitor type.

However, in the case of reproduction of a multilayer (two or more layer) BD, the output of the laser diode is required to be about 10 times greater than that in the case of reproduction of a single-layer BD. Therefore, in order to support reproduction of multilayer BD, the laser output control circuit depicted in FIG. 3 is required to use two variable resistors and adjust them depending on single-layer and multilayer BDs, respectively, and it is also required to further add a switch circuit that switches the two variable resistors.

An optical pickup apparatus according to an aspect of the present invention, includes: a first laser light source including a first laser diode configured to emit a laser beam having a first wavelength, and a back monitor photodetector configured to receive the laser beam emitted from the first laser diode in a backward direction, which is not a direction of an optical disc, and output a first monitor signal; a second laser light source including a second laser diode configured to emit a laser beam having a second wavelength; a light-receiving circuit including a front monitor photodetector configured to receive the laser beam emitted from the second laser diode in a forward direction, which is a direction of the optical disc, and output a second monitor signal, and a switch circuit configured to be inputted with the first and the second monitor signals, and output one of the first and the second monitor signals according to a switch signal; a first drive circuit configured to drive the first laser diode according to the first monitor signal outputted from the light-receiving circuit; and a second drive circuit configured to drive the second laser diode according to the second monitor signal outputted from the light-receiving circuit.

Other features of the present invention will become apparent from descriptions of this specification and of the accompanying drawings.

For more thorough understanding of the present invention and advantages thereof, the following description should be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit block diagram illustrating a configuration of a laser output control circuit of an optical pickup apparatus according to one embodiment of the present invention;

FIG. 2 is a circuit block diagram illustrating an example of a specific configuration of a VI converter circuit;

FIG. 3 is a circuit block diagram illustrating an example of a configuration of a typical laser output control circuit of back monitor type; and

FIG. 4 is a circuit block diagram illustrating an example of a configuration of a typical laser output control circuit of front monitor type.

At least the following details will become apparent from descriptions of this specification and of the accompanying drawings.

===Configuration of Laser Output Control Circuit===

Description will hereinafter be given of a configuration of a laser output control circuit of an optical pickup apparatus according to an embodiment of the present invention with reference to FIGS. 1 and 2 . In an embodiment of the present invention, by way of example, the optical pickup apparatus is configured to perform both recording and reproduction for CD and DVD and perform only reproduction for single-layer and multilayer BD.

The laser output control circuit depicted in FIG. 1 is configured to control outputs of laser diodes LD 1 and LD 2 , and includes photodiodes PD 1 , PD 2 , ADCs 12 , 22 , LD drive circuits 13 , 23 , current sources 14 , 24 , and a light-receiving circuit 30 . The light-receiving circuit 30 is controlled by a controller 50 .

The (first) laser diode LD 1 is capable of emitting a blue-violet laser beam in the waveband of 405 nm, and is used for reproduction of BD. The laser diode LD 1 and the photodiode PD 1 are provided within the same package, configured as a (first) laser light source 11 . The cathodes of the laser diode LD 1 and the photodiode PD 1 are connected to the common ground.

The (second) laser diode LD 2 is capable of emitting an infrared laser beam in the waveband of 780 nm and a red laser beam in the waveband of 650 nm, and is used for recording/reproduction of CD/DVD. The laser diode LD 2 and the photodiode PD 2 are provided within the same package, configured as a (second) laser light source 21 . The cathodes of the laser diode LD 2 and the photodiode PD 2 are connected to the common ground. The anode of the photodiode PD 2 is in an open state.

The light-receiving circuit 30 includes a photodiode PDfm, a resistor 31 , a VI (voltage/current) converter circuit 32 , a switch circuit 33 , and an IV amplifier 34 , and is configured as an integrated circuit provided with at least a terminal INbm. The terminal INbm is connected to the anode of the photodiode PD 1 , and a current Ibm 1 flowing through the photodiode PD 1 is inputted via the terminal INbm to the light-receiving circuit 30 .

The photodiode PDfm is disposed so as to receive the laser beam emitted forward (in a forward direction) from the laser diode LD 2 , and the anode thereof is connected to the ground. The resistor 31 has one end connected to the terminal INbm, and the other end connected to the ground.

As depicted in FIG. 2 , the VI converter circuit 32 includes an operational amplifier OP, a (NPN) transistor Q 1 , and a resistor R 1 . A voltage Vbm 1 of the terminal INbm is applied to the non-inverting input of the operation amplifier OP, and the output thereof is connected to the base of the transistor Q 1 . The resistor R 1 has one end connected to the emitter of the transistor Q 1 and the other end thereof connected to the ground. Further, a voltage Vbm 2 at a connection point between the transistor Q 1 and the resistor R 1 is applied to the inverting input of the operational amplifier OP. The collector of the transistor Q 1 acts as an output node to output a current Ibm 2 .

The switch circuit 33 is configured to connect the input node of the IV amplifier 34 with the output node of the VI converter circuit 32 or the cathode of the photodiode PDfm. The current Ibm 2 outputted from the VI converter circuit 32 or the current Ifm flowing through the photodiode PDfm is inputted via the switch circuit 33 to the IV amplifier 34 . The switch circuit 33 is capable of switching the connection in response to a switch signal SW inputted from the controller 50 .

The IV amplifier 34 can be configured using an operational amplifier whose inverting input and output are connected via resistors, for example, and a voltage signal Vm outputted from the IV amplifier 34 is inputted via the ADCs 12 and 22 to the LD drive circuits 13 and 23 , respectively. The IV amplifier 34 includes a plurality of resistors for selecting a gain and a switch circuit (not depicted) configured to switch a resistor to be connected, and is capable of adjusting the gain according to a selection signal SEL inputted from the controller 50 .

The LD drive circuit 13 (first drive circuit) is configured to control the current source 14 , and the current source 14 is configured to supply a drive current Ild 1 to the anode of LD 1 . The LD drive circuit 23 (second drive circuit) is configured to control the current source 24 , and the current source 24 is configured to supply a drive current Ild 2 to the anode of LD 2 .

===Operation of Laser Output Control Circuit===

Description will hereinafter be given of an operation of the laser output control circuit of the optical pickup apparatus according to an embodiment of the present invention.

Firstly, description will be given of an operation when performing recording/reproduction of CD/DVD. It should be noted that, when performing recording/reproduction of CD/DVD, the controller 50 is configured to input the switch signal SW to the switch circuit 33 , thereby connecting the input node of the IV amplifier 34 and the cathode of the photodiode PDfm. The controller 50 is configured to input the selection signal SEL to the IV amplifier 34 , thereby selecting a gain for CD or DVD as a gain of the IV amplifier 34 .

When the drive current Ild 2 is supplied from the current source 24 and the laser beam is emitted from the laser diode LD 2 , the photodiode PDfm receives the laser beam emitted forward from the laser diode LD 2 . The current Ifm according to the intensity of the received laser beam flows through the photodiode PDfm, and the current Ifm is inputted via the switch circuit 33 to the IV amplifier 34 as a sink current. In an embodiment of the present invention, the current Ifm corresponds to a second monitor signal.

The IV amplifier 34 is configured to convert the current Ifm into the voltage signal Vm according to the gain. The ADC 22 is configured to further convert the voltage signal Vm into a digital signal. The LD drive circuit 23 is configured to control the drive current Ild 2 supplied from the current source 24 according to the voltage signal Vm converted into the digital signal, thereby controlling the output of the laser diode LD 2 .

As such, the current Ifm flowing through the front monitor photodiode PDfm of the light-receiving circuit 30 is converted into the voltage signal Vm using the IV amplifier 34 and used as the monitor signal, thereby being able to control the output of the laser diode LD 2 at high speed and perform not only reproduction of CD/DVD but also recording thereof.

Secondly, description will be given of an operation when performing reproduction of single-layer or multilayer BD. When performing reproduction of BD, the controller 50 inputs the switch signal SW to the switch circuit 33 , thereby connecting the input node of the IV amplifier 34 and the output node of the VI converter circuit 32 . The controller 50 inputs the selection signal SEL to the IV amplifier 34 , thereby selecting a gain for BD as a gain of the IV amplifier 34 .

When the drive current Ild 1 is supplied from the current source 14 and the laser beam is emitted from the laser diode LD 1 , the photodiode PD 1 receives the laser beam emitted backward (in a backward direction) from the laser diode LD 1 . The current Ibm 1 according to the intensity of the received laser beam flows through the photodiode PD 1 , and the current Ibm 1 is inputted via the terminal INbm to the light-receiving circuit 30 as a source current. In an embodiment of the present invention, the current Ibm 1 corresponds to a first monitor signal.

The current Ibm 1 flows through the resistor 31 and the voltage (voltage of the terminal INbm) Vbm 1 generated across the resistor 31 is inputted to the VI converter circuit 32 . In the VI converter circuit 32 depicted in FIG. 2 , the current Ibm 2 (=Vbm 1 /R 1 ) flows through the transistor Q 1 so that the voltage Vbm 1 and the voltage Vbm 2 become equal to each other, and the current Ibm 2 is inputted via the switch circuit 33 to the IV amplifier 34 as a sink current.

The IV amplifier 34 is configured to convert the current Ibm 2 into the voltage signal Vm according to the gain. The ADC 12 is configured to further convert the voltage signal Vm into a digital signal. The LD drive circuit 13 is configured to control the drive current Ild 1 supplied from the current source 14 according to the voltage signal Vm converted into the digital signal, thereby controlling the output of the laser diode LD 1 .

As such, when performing reproduction of BD, the current Ibm 1 flowing through the back monitor photodiode PD 1 provided in the laser light source 11 is converted into the voltage signal Vm using the resistor 31 , the VI converter circuit 32 , and the IV amplifier 34 , and is used as the monitor signal. Although there is a difference, by about ten times, in magnitude of the output of the laser diode LD 1 between the cases of reproduction of single-layer BD and reproduction of multilayer BD, as described above, a variable range of the IV amplifier 34 is sufficiently wide (e.g., 40 dB), thereby being able to support the reproduction of both types of BDs.

In an embodiment of the present invention, the current Ibm 1 inputted as the source current is converted into the sink current Ibm 2 in the same direction as that of the current Ifm, to be inputted to the switch circuit 33 , using the resistor 31 and the VI converter circuit 32 . Therefore, for example, in the case where the current Ibm 1 and the current Ifm flow in the same direction such as when the cathode of the photodiode PDfm is connected to the ground, the resistor 31 and the VI converter circuit 32 are not necessary.

As described above, in the laser output control circuit of the optical output apparatus depicted in FIG. 1 , the first monitor signal outputted from the back monitor photodiode PD 1 is inputted to the light-receiving circuit 30 when performing reproduction of BD, and the switch circuit 33 switches the first monitor signal to the second monitor signal outputted from the front monitor photodiode PDfm included in the light-receiving circuit 30 when performing recording/reproduction of CD/DVD, thereby being able to support reproduction of multilayer BD without adjusting a variable resistor depending on single-layer and multilayer BDs.

Further, the current flowing through the photodiode PD 1 or the photodiode PDfm is converted into the voltage signal Vm with the IV amplifier 34 , and thus the LD drive circuits 13 and 23 are able to respectively control the outputs of the laser diode LD 1 and LD 2 according to the voltage signal Vm.

Further, the voltage Vbm 1 generated across the resistor 31 through which the current Ibm 1 , flowing through the photodiode PD 1 , flows is converted into the current Ibm 2 , thereby being able to input the current Ibm 2 and the current Ifm to the switch circuit 33 as the sink currents in the same direction.

Further, the light-receiving circuit (integrated circuit) 30 includes: the terminal INbm configured to inputted with the first monitor signal outputted from the back monitor photodiode PD 1 ; the front monitor photodiode PDfm configured to output the second monitor signal; and the switch circuit 33 configured to switch the monitor signals, thereby being able to output, as the monitor signal, the first monitor signal when performing reproduction of BD and the second monitor signal when performing recording/reproduction of CD/DVD, respectively.

Further, using the light-receiving circuit (integrated circuit) 30 , the first monitor signal is inputted to the terminal INbm when performing reproduction of BD, and a laser beam is received by the front monitor photodiode PDfm when performing recording/reproduction of CD/DVD, thereby being able to control each of the outputs of the laser diode LD 1 and LD 2 according to the monitor signal outputted from the light-receiving circuit (integrated circuit) 30 , and therefore, reproduction of multilayer BD can be supported without adjusting a variable resistor depending on single-layer and multilayer BDs.

The above embodiments of the present invention are simply for facilitating the understanding of the present invention and are not in any way to be construed as limiting the present invention. The present invention may variously be changed or altered without departing from its spirit and encompass equivalents thereof.