JP2006303135A - Laser driving circuit and disk playback apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the light emitting peak power upon driving a high-frequency superposition laser diode not higher than the level for ensuring read stability. <P>SOLUTION: A high-frequency sinusoidal current output from a high-frequency oscillator 1 is superposed on the anode side of a laser diode LD, which is DC driven via a transistor Q2, through a high-frequency current clipping circuit 3. Thus, a high-frequency current having a sinusoidal waveform whose positive side clipped peak is superposed on a DC current to drive the laser diode LD. Thus, the light emitting peak power of the laser diode LD is suppressed not to exceed 2.5 times, and recorded information is not erased upon reading, so that read stability can be ensured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a disc recording / reproducing apparatus for a Blu-ray disc, and more particularly to a laser driving circuit that superimposes a high-frequency current on the driving current of a laser diode during reproduction.

  In a recording / reproducing apparatus for a phase change disk using a laser diode (hereinafter referred to as LD), the recording / reproducing power specification of the disk is about 5.0 mW at the time of recording, about 3 mW at the time of erasing, and 300 uW at the time of reading. . Therefore, the laser diode emits light with three levels of power. Further, when the laser diode is DC-driven during disk reproduction (for example, see Patent Document 1), the power of irradiation light to the optical disk fluctuates and becomes unstable due to the return light from the optical disk. And the influence of the return light is suppressed by lowering the drive current to the oscillation off region.

  FIG. 7 is a circuit diagram showing a conventional configuration example of a driving circuit for a laser diode of a high frequency superposition driving method. The laser diode LD is driven by supplying a DC current from the voltage Vcc to the anode side through the resistor R7 and the transistor Q2. The high frequency superimposed on the DC drive current of the laser diode LD is output by the high frequency oscillator 1, and the high frequency oscillator 1 is variable in oscillation frequency and amplitude by an external current. The output of the sine wave of the high-frequency oscillator 1 is converted into a current by the resistor R8 and the transistor Q3, and further amplified by the transistor Q4 and the resistors R9 and R10, and then superimposed on the anode side of the laser diode LD. Drive.

  On the other hand, 2 constitutes an APC circuit, the optical output of the laser diode LD is received by the photodiode PD, the current is amplified by the operational amplifier IC1, and this current is set in the error comparison amplifier of IC2, for example, a read power voltage Compared with Vref, the error voltage is converted into a current by the resistor R5 and the transistor Q1, and forms a feedback circuit that feeds back to the base of the transistor Q2. Thereby, the optical output of the laser diode LD is feedback-controlled to the read power level. The capacitor C1, resistor R4, and resistor R3 connected to the error comparison amplifier IC2 form a loop filter. Further, by changing the voltage Vref set in the error comparison amplifier IC2 at the time of writing and erasing, the optical output of the laser diode LD can be changed to the writing power and the erasing power.

As described above, since the laser diode LD emits light with three levels of power, if the coupling of the optical path system is 18 to 20%, the output of the LD needs to be 33.3 mW or more. For this reason, a large recording power is required, and a large output LD is used. For example, when a recording power of about 40 mW with a margin of 5.0 mW is used, only a read power of 0.3 mW is allowed. Then, the output of the LD needs to be 1.5 mW.
JP-A-3-171687 (page 540, FIG. 1)

  A laser diode generally has a noise characteristic as shown in FIG. 8 because noise is almost constant from a certain output. Since this noise characteristic curve is almost constant, in a high output LD, the noise becomes large at 1.5 mW, the RIN is poor, and this causes a reduction in C / N during reproduction. As a solution to this problem, there is a method of further reducing the coupling at the time of reading and using it in a place where RIN is small. For example, if 6.0 dB of ATT (50% transmittance) is inserted, the power of the LD becomes 3.0 mW. In this case, the high frequency superposition level increases by about 1.2 times.

  The durability (read stability) of the recording signal at the time of reading is determined by the read power, but greatly depends on the high frequency superimposition level. For this reason, unless the peak power of the high-frequency superimposed wave is managed, the durability of the recording signal at the time of reading is impaired, but the current level adjustment has a large variation and becomes 6 to 9 times. Further, the temperature characteristics of the LD optical output versus forward current are as shown in FIG. 9, and the high-frequency superposition effect also changes with temperature, and the above-described variation becomes more widespread.

  FIG. 10 is a characteristic diagram showing the relationship between the high frequency superimposition level versus peak value and RIN. When Ith is set to 2.0 mA / 2.0 mW, the RIN and emission peak value characteristics are 1.5 mW to 6.0 mW. Looking at it, it becomes 4.5 times to 8.0 times. If the read power is 300 uW and the multiple (this multiple varies with temperature) is 8, it will be 2.4 mW, reaching half of 5.0 mW of the write power, and 60% of the erase power of 4.0 mW. That is, it is easy to disappear as it is, and the durability of the recording signal at the time of reading deteriorates. Note that if the LD characteristic, high frequency superposition frequency, and level change, the multiple will change, and if the superposition level is increased or the frequency is lowered, the peak power will increase.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a laser driving circuit capable of reducing the emission peak power when driving a high-frequency superimposed laser diode to a level that can ensure lead stability and An object of the present invention is to provide a disk reproducing apparatus using this drive circuit.

  In order to achieve the above object, the present invention comprises a laser driving circuit for driving a DC-driven laser diode with a high-frequency current superimposed thereon, comprising a high-frequency current clipping circuit for clipping a peak portion of the high-frequency current. Features.

  Further, the present invention is a package in which a circuit for feedback control of the DC level is integrated so that the laser diode driven by DC is superimposed with a high frequency current and the light emission power of the laser diode becomes a set level. The laser driving circuit is characterized in that it comprises a high-frequency current clipping circuit that clips a peak portion of the high-frequency current.

  The present invention also includes a laser drive circuit that drives a high-frequency current superimposed on a DC-driven laser diode, irradiates the disk with laser light emitted from the laser diode, receives the reflected light, and receives information. The laser drive circuit includes a high-frequency current clipping circuit that clips a peak portion of the high-frequency current.

  As described above, in the present invention, when the peak portion of the high-frequency current superimposed on the DC-driven laser diode to eliminate the influence of the return light from the disk is clipped, the peak value of the emission power of the laser diode at the time of reading is obtained. It has been experimentally found that it can be suppressed to 2.5 times or less, and as a result, lead stability can be ensured.

  According to the present invention, by providing a circuit that clips a peak portion of a high-frequency current superimposed on a DC-driven laser diode, the light emission power of the laser diode at the time of reading is reduced to a level that can ensure read stability. Can do.

  The purpose of reducing the emission peak power during driving of the high-frequency superimposed laser diode to a level that can ensure read stability is realized by providing a circuit that clips the peak portion of the high-frequency current superimposed on the DC-driven laser diode.

  FIG. 1 is a circuit diagram showing a configuration example of a laser driving circuit according to the first embodiment of the present invention. However, the same parts as those in the conventional example will be described with the same reference numerals. The laser driving circuit includes a high-frequency oscillator 1, an APC circuit 2, a high-frequency current clipping circuit 3, and a laser diode LD. The APC circuit 2 is composed of main components such as a photodiode PD, an operational amplifier IC1, an error comparison amplifier IC2, a voltage-current conversion circuit 21, an LD driving transistor Q2, and the high-frequency current clipping circuit 3 includes a coupling capacitor C2. , An input resistor R8, a clipping transistor Q3, an emitter resistor R9 of the transistor Q3, resistors R10 and R11 constituting a base bias circuit of the transistor Q3, and a capacitor C3.

  Next, the operation of this embodiment will be described. The laser diode LD is driven by supplying a DC current from the voltage Vcc to the anode side through the resistor R7 and the transistor Q2. A high-frequency current superimposed on the drive current of the laser diode LD is output by a high-frequency oscillator 1, and the oscillation frequency and amplitude of the high-frequency oscillator 1 are variable by an external current. The high frequency current of the sine wave output from the high frequency oscillator 1 is clipped by the high frequency current clipping circuit 3 as shown in FIG. 2, and the clipped high frequency current is fed to the anode side of the laser diode LD. Superimposed to drive the laser diode LD.

  FIG. 3 is a circuit diagram for explaining the operation of the high-frequency current clipping circuit 3. When a high-frequency current is not input to the emitter of the transistor Q3, the current I flows from the collector side of the transistor Q3 as currents I1 and I2 through the emitter to the resistors R9 and R8 by the base bias circuit of the transistor Q3. Here, when a high-frequency current is input through the capacitor C2 and the resistor R8, the current I1 flowing through the resistor R8 decreases on the positive side of the high-frequency current, and the current I2 flowing through the resistor R8 increases correspondingly to increase the emitter voltage. To increase. When the emitter voltage increases to a predetermined voltage, the transistor Q3 is cut off, and the current output to the collector side of the transistor Q3 is clipped as shown in FIG. On the other hand, since the current I1 flows through the resistor R9 on the negative side of the input high-frequency current, the emitter voltage does not rise and the transistor Q3 is not cut off, and a normal sinusoidal high-frequency current flows as shown in FIG. .

  Thus, when a high-frequency current having a waveform with the positive side clipped is superimposed on the DC current and flows into the laser diode LD, the LD emits light. The light emission level at this time is received by the photodiode PD, and the current is amplified by the operational amplifier IC1, and this current is compared with, for example, the read power voltage Vref set in the error comparison amplifier IC2, and the error voltage is the resistance R5. The light is converted into a current by the transistor Q1 and fed back to the base of the transistor Q2, whereby the optical output of the laser diode LD is controlled to the read power level.

  Here, when the laser diode LD on which the high-frequency current having a waveform such that the positive side is clipped as described above is driven, the multiple of the peak output with respect to the light emission output of the laser diode LD becomes 100 as shown in FIG. As shown, it is suppressed at any frequency and is 2.5 times or less. In the figure, 200 indicates a multiple of the peak output with respect to the light emission output of the conventional LD.

  FIG. 5 is a waveform diagram showing the relationship between the light emission level of the laser diode LD and the superimposed high-frequency current. FIG. 5B is related to the present embodiment, and it can be seen that the peak power of the light emission level of the laser diode LD is suppressed as compared with the conventional one shown in FIG. In order to suppress the peak power of this light emission, it can be seen that a superposed high-frequency current may be used as shown in FIG.

  According to this embodiment, in the disk recording / reproducing apparatus using the laser diode LD, the peak power of the high-frequency current superimposed when the laser diode LD is driven is clipped, so that The magnification can be suppressed to a maximum of 2.5 times or less. Thereby, even if the light emission power at the time of reading changes, the read stability is not greatly affected, and the durability of the recording signal at the time of reading can be ensured.

  FIG. 6 is a circuit diagram showing a configuration example of a laser driving circuit according to the second embodiment of the present invention. However, the same parts as those in the conventional example will be described with the same reference numerals. The laser drive circuit of this example is made into an IC, and the conventional laser drive circuit (see FIG. 7) is all packaged in the LDDIC unit 8 and packaged. The difference is that a high-frequency current clipping circuit 9 is inserted between the output terminal of the LDDIC unit 8 and the laser diode LD.

  Next, the operation of this embodiment will be described. The clipping operation of the high frequency superimposed current is performed by inserting RFC1 between the output of the LDDIC unit 8 and the laser diode LD to increase the impedance with respect to the high frequency superimposed frequency, and the LDDIC unit 8 by the base-grounded transistor Q11 having a small input impedance. The high frequency superimposed current almost flows through the transistor Q11. Since the transistor Q11 is biased by the resistors R11 and R12 and grounded by the emitter resistor R13, the transmission of the positive current at the time of high frequency superposition is determined by the emitter current, and a larger current cuts off the transistor Q11, As a result, the peak of the high-frequency current is clipped.

  In the example of FIG. 6, the resistor R11 is connected to the output terminal of the LDDIC unit 8. However, when Vop varies, the bias is stabilized when taken from Vcc. In the example of FIG. 6, the current is determined by the resistor R13 so as not to be complicated, but may be configured by a constant current.

  Here, since the impedance of RFC1 decreases at a low frequency (1 MHz or less), it does not affect the APC response. For example, if RFC is 1 uH, the frequency is 6Ω at 1 MHz, and 1.88 KΩ when the frequency of the high-frequency current is 300 MHz. This is because the capacitance Ct of the laser diode LD, the output capacitance of the LDDIC unit 8, and the transmission path capacitance are sufficiently small and sufficiently large for the internal resistance Rd of 15 to 20Ω of the LD. In addition, in the example of clipping, when the superimposed current is 10 mAp-p, in order to clip positive 5 mA, a resistor R11, R12 must be biased to the base of the transistor Q11 so that 5 mA flows through the resistor R13. It ’s fine.

  According to the present embodiment, when the laser drive circuit is an IC, if the high-frequency current clipping circuit 9 is inserted between the output and the laser diode LD, the same peak as in the first embodiment is clipped. Since the high-frequency current is superimposed on the LD and the laser diode is driven, the same effect as in the first embodiment can be obtained. In particular, in the present embodiment, an IC laser driving circuit can be used as it is, and the configuration is more practical without violating downsizing of the apparatus.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. When the laser drive circuit of the above embodiment is mounted on a Blu-ray disc playback device, stable read stability can be ensured without erasing the recorded signal on the disc during reading.

1 is a circuit diagram illustrating a configuration example of a laser drive circuit according to a first embodiment of the present invention. FIG. 2 is a waveform diagram showing a high-frequency current waveform superimposed on the laser diode shown in FIG. 1. It is a circuit diagram explaining operation | movement of the high frequency current clipping circuit shown in FIG. It is the characteristic view which showed the relationship between the optical output of a laser diode, and the multiple of a peak value. It is the wave form diagram which showed the relationship between the light emission level of a laser diode, and a superimposed high frequency current. It is the circuit diagram which showed the structural example of the laser drive circuit which concerns on the 2nd Embodiment of this invention. It is the circuit diagram which showed the example of the conventional structure of the laser drive circuit of a high frequency superposition drive system. It is the characteristic view which showed the relationship between the optical output of a laser diode, and RIN. It is the figure which showed the temperature characteristic of the optical output of a laser diode versus forward current. It is the characteristic figure which showed the relationship between the optical output high frequency superimposition level versus peak value of a laser diode, and RIN.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... High frequency oscillator, 2 ... APC circuit, 3, 9 ... High frequency current clip circuit, 8 ... LDDIC part, 21 ... Voltage current circuit, C2 ... Coupling capacitor, C3 ... Capacitor, IC1 ... Operational amplifier, IC2: Error comparison amplifier, LD: Laser diode, PD: Photodiode, Q2: LD driving transistor, Q3: Clipping transistor, R1, R2, R3, R4, R5, R6, R7 , R8, R9, R10, R11, R12, R13 ... resistors.

Claims (6)

A laser driving circuit for driving a DC-driven laser diode with a high-frequency current superimposed thereon,
A high-frequency current clipping circuit for clipping a peak portion of the high-frequency current;
A laser driving circuit.   2. The laser drive circuit according to claim 1, further comprising a circuit for performing feedback control of the DC drive level so that the light emission power of the laser diode becomes a set level. A laser driving circuit in which a high frequency current is superimposed on a laser diode that is DC driven and a circuit for feedback control of the DC level is integrated so that the light emission power of the laser diode becomes a set level. Because
A high-frequency current clipping circuit for clipping a peak portion of the high-frequency current;
A laser driving circuit.   4. The laser driving circuit according to claim 3, wherein the high-frequency current clipping circuit is connected to a terminal for connecting the laser diode to the laser driving circuit, and the laser diode is connected via the high-frequency current clipping circuit. . A disk reproducing apparatus comprising a laser driving circuit for driving a high-frequency current superimposed on a DC-driven laser diode, irradiating the disk with laser light emitted from the laser diode, and receiving the reflected light to reproduce information Because
The laser driving circuit includes a high-frequency current clipping circuit that clips a peak portion of the high-frequency current.
A disc player characterized by that. 6. The disc reproducing apparatus according to claim 5, wherein the wavelength of the laser beam emitted from the laser diode is 407 nm, and the disc is a Blu-ray disc.

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