JPS63304435A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To overwrite and record a signal on an optical disk by an optimum power by independently setting the lower limit and the upper limit of a laser output by first and second current sources respectively, when the signal is recorded. CONSTITUTION:The laser output is monitored by a light receiving element 2, and a first servo circuit (first current source) is constituted of the light receiving element 2, an I/V conversion circuit 3, an error amplifier 4, a sampling circuit 5, the current source 6 and a semiconductor laser LD, and a second servo circuit (second current source) is constituted of a peak holding circuit 7, the error amplifier 8, the current source 9, a switch SW3, the laser LD, the light receiving element 2 and the I/V conversion circuit 3, and a laser output power level is kept higher than the level by the first current source, by the second current source, and a recording power is determined by the output Vr of a voltage source VR. Because in this constitution, the upper and the lower limits of the laser output at the time of the recording are set independently by the first and second current sources, the signal can be overwritten and recorded on the disk by the optimum power.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser drive circuit for an optical disk device for overwriting or recording information on a rewritable or write-once optical disk and reproducing the recorded information. In particular, the present invention relates to a semiconductor laser drive circuit that allows information to be overwritten on a phase change type rewritable optical disk using a single light spot.

Conventional technology The conventional method for overwriting information on a phase-change type rewritable optical disc is to use an oblong erasing light spot that precedes a roughly circular recording light spot to erase old information that has already been recorded. A so-called two-spot method is known in which the information is erased and new information is then recorded using a recording light spot.

Recently, a so-called one-spot method has been developed in which recording media can be crystallized at a faster speed and can be overwritten using only one approximately circular light spot. FIG. 4 shows changes in the output power of the semiconductor laser when overwriting with this method. When the reproduction section changes to the erasure section, the output power is first increased from the reproduction power to the erasure power. Furthermore, when entering the recording period, the output power is intensity-modulated according to the recording signal.In order to obtain such output power, conventionally, two current sources are used in the semiconductor laser, which outputs the average power of the erase power and the recording power. A semiconductor laser drive circuit is known that combines a current source configured to do this and a current source that outputs the difference between recording power and erasing power. The operation of this circuit will be explained below.

First, the former current source is directly connected to a semiconductor laser to output a predetermined power. The latter current source modulated by the recording signal is then AC coupled to the semiconductor laser.

In this way, the output power of the semiconductor laser can be modulated between recording and erasing powers.

Problems to be Solved by the Invention However, the above-mentioned configuration has a problem in that the two electric currents become extremely complicated. That is, when overwriting a constant-rotation rewritable optical disk, it is necessary to set recording power and erasing power independently according to changes in linear velocity, but it is difficult to deal with this with the above configuration. Such a request also occurs when optical disks with different overwriting characteristics are to be handled by the same optical disk drive.

Furthermore, recording on conventional write-once optical discs is also required. In the write-once type, it is necessary to reduce the power equivalent to the above-mentioned erasing power to about O or the playback power, so the number of types of power settings increases, and the power setting with the above configuration also has the problem of becoming more complicated. Ta.

In view of this, an object of the present invention is to provide a semiconductor laser drive circuit in which recording power and erasing power can be set independently. A further object of the present invention is to provide a semiconductor laser drive circuit that can handle recording on write-once optical discs in addition to overwriting on rewritable optical discs.

Means for Solving the Problems The present invention includes a light receiving element that detects the output power of a semiconductor laser as a monitor signal, and a light receiving element that detects the output power of the semiconductor laser as a monitor signal, and a light receiving element that detects the output power of the semiconductor laser so that the output power of the semiconductor laser reaches a first level with reference to the monitor signal. a first current source that causes a current to flow through the semiconductor laser; and a current source that superimposes a current on the semiconductor laser so that the output power of the semiconductor laser becomes a second level higher than the first level with reference to the monitor signal. This is a semiconductor laser driving circuit including a second current source that causes a current to flow, and a modulation means that receives a recording signal and modulates the second current source.

Effect of the Invention With the above-described configuration, the present invention allows the lower limit and main point of the output power of the semiconductor laser to be set independently by the first and second current sources when recording a signal, thereby preventing overwriting and overwriting on a rewritable optical disc. Recording on the write-once optical disc can be performed with n optimum power.

Embodiment FIG. 1 is a block diagram of a semiconductor laser drive circuit in an embodiment of the present invention. In FIG. 1, LD is a semiconductor laser to be driven. 1 shows the entire semiconductor laser drive circuit in this embodiment, and the terminal T1
The semiconductor laser LD is driven through the LD. This semiconductor laser drive circuit 1 consists of two current source blocks based on servo control. After that, each current source block is
and a second servo circuit. Servo control of the first and second servo circuits is executed in a time-divisionally switched manner using an external signal. In the following, we will first explain this semiconductor laser drive circuit 1.
The components will be explained, and then the operations of the first and second servo circuits will be explained. Next, we will explain how to actually record on an optical disc.

Reference numeral 2 denotes a light receiving element, which extracts a monitor current In proportional to the output power of the semiconductor laser LD using a PIN diode usually housed in the same package as the semiconductor laser LD. 3 is a current-voltage conversion circuit which converts the monitor current Im into a monitor voltage vm and outputs the same. vP is a voltage source that outputs a voltage vp that determines reproduction power, and VX is a voltage source that outputs a voltage ve that determines erase power. Normal Vθ〉v
Let p>0. The output voltage V of the voltage source VR is changed in accordance with a command signal from an outside (not shown). For example, a D-person converter can be used for this purpose.

SWl is an erase gate signal K indicating the erase section of the external force)
This switch selects the voltage Vp as the voltage Vp when RGT is 0, and selects the voltage ve as the voltage VO when it is 1. VOFF is a voltage source that outputs a voltage VofT that sets the drive current of the semiconductor laser LD to 0 and completely stops light emission.

Here, the monitor voltage vm is assumed to be output in the positive direction with respect to the ground, and the voltage Voff is selected to be negative. This is because if only the voltage Voff is set to 0, a threshold current may flow through the semiconductor laser LD only by the servo control described below. In other words, if the monitor voltage vm becomes apparently negative due to the offset of the current-voltage conversion circuit 6 (even if the semiconductor laser LD does not emit light), the servo control described later will cause the semiconductor laser to emit a small amount of light, that is. This results in a threshold current flowing.

When the light emission command signal LDON of the semiconductor laser LD from the outside is 0 (non-emission command), SW2 sets the voltage vo.
This switch selects the voltage VO as vl when ff is equal to 1 (light emission command). 4 is the voltage v2 obtained by amplifying the value obtained by subtracting the monitor voltage vm from the voltage v1.
This is an error amplifier that outputs as follows. 5 is a sample hold circuit, which receives a recording gate signal W indicating a recording section from the outside.
When TGT is 0, it is in the sample state and the error amplifier 4
Outputs the voltage v2 outputted by as it is as voltage v3,
When the recording gate signal WT (, T is 1, it enters a hold state and outputs vP just before the recording gate signal WTGT becomes 1 as a voltage v3. 6 is a current source that outputs a current 3 proportional to the input voltage v3. Then, a current 3 is applied to the semiconductor laser LD via the terminal T1.However, when the voltage v3 is negative, the current I3=◯.

The parts explained above, namely the light receiving element 2, the current-voltage conversion circuit 3, the error amplifier 4, the sample hold circuit 6,
A portion consisting of the current source 6 and the semiconductor laser LD constitutes a first servo circuit (first current source block).

7 is a peak hold circuit that detects the maximum value of monitor voltage vm and outputs it as voltage v4.

However, as will be described later, the voltage v4 is defined so that it decreases with an appropriate time constant. VR is a voltage source for outputting a voltage vr that determines the recording power, and the output voltage vr is changed by an external command signal (not shown). Similar to the voltage source vE, a D-A converter is used for this as well. 8 is an error amplifier that amplifies the value obtained by subtracting the voltage v4 from the voltage vr and outputs it as a voltage v5. However, when the recording gate signal WT(,T) is 0, the error amplifier 8 outputs the voltage v5 as Ov regardless of the input. (However, when the voltage v6 is negative, the current is 15-0. This is a switch connected to the semiconductor laser LD (via terminal T1), that is, switch S
The intensity of the semiconductor laser LD is modulated by W3.

Peak hold circuit7. Error amplifier 8. Current source 9, switch SW3. Semiconductor laser LD, light receiving element 2. The current-voltage variable circuit 3 constitutes a second servo circuit (second current source block).

The operation of the semiconductor laser drive circuit of this embodiment configured as described above will be explained separately for the first servo circuit and the second servo circuit.

The first servo circuit described above receives the recording gate signal %WTG.
When 'r% is 0, the output power of the semiconductor laser LD is servo controlled (so-called power servo). At this time, since the current of the current source 9 caused by the second servo circuit is 0, it is assumed that the current flowing to the semiconductor laser LD is only that of the current source 6.

When the light emission command signal LDON=O, the voltage v1 becomes negative. On the other hand, since the monitor voltage Vm does not become negative, the output voltage v2 of the error amplifier 4 becomes negative. At this time, the current l3
=O, and the semiconductor laser LD does not emit light. This state remains stable. Here, when the light emission command signal LDON=1, the voltage v1 is changed to the voltage V1 according to the erase gate signal ERGT.
p is set to one of the positive voltages of voltage Vθ. Sont
Since the semiconductor laser LD did not emit light, the monitor voltage V
.

is 0. Therefore, the output of error amplifier 4 is positive,
An electric current 3 flows through the semiconductor laser LD.

The semiconductor laser LD emits light and outputs power.

A monitor voltage vm proportional to this voltage is fed back to the error amplifier 4. As a result, power servo can be realized. The output power is switched to the reproduction power or the erase power depending on the erase gate signal KR (1, 0°1 of T).Here, when the recording gate signal w'rc'r=1, the sample hold circuit 6 changes from the sample state to the hold state. state, and the voltage v3 that was output just before is held.The current X3 is also held in the same way.At this time, if the current source 9 remains 0, the output power of the semiconductor laser LD does not change.The recording gate signal WTGT is When it returns to 0, it returns to the sample state.

On the other hand, in the second servo circuit, when the recording gate signal WTGT is 0, the current source 9 does not work and the servo is not effective.

Assume here that the recording gate signal WTGT becomes 1. A current 3 by the first servo circuit is already flowing through the semiconductor laser LD. The corresponding voltage v4 (voltage v
e or less) enters one input of the error amplifier 8 from the peak hold circuit 7. The other input is a voltage vr that determines the recording power. Since the voltage vr is set higher than the voltage ve, the output voltage v6 of the error amplifier 8 becomes positive and the current voltage 5 is outputted to the current source 9. When the recording gate WTGT is set to 1, the recording signal WTDT is also input as a data string of o, 1 at the same time.

At this time, when the recording signal WTDT becomes 1, the electric current 5 flows to the semiconductor laser LD via the switch SW3. The sum of currents 3 and 5 flows through the semiconductor laser LD, and a corresponding power is output. The monitor voltage V at this time is fed back from the peak hold circuit 7 to the error amplifier 8 as a voltage v4, and servo control can be realized so that the voltage Vr and the voltage v4 match. The output power at this time becomes the recording power. The current X5 flows to compensate for the difference between the recording power and the power generated by the current generator 3. When the recording signal WTDT becomes 0, the electrician 5 switches the semiconductor laser LD.
Only the electric current worker 3 flows without flowing. semiconductor laser LD
Erase or playback power is output. Note that the time constant given to the voltage v4 of the peak hold circuit 7 is selected to be close to the longest time during which the recording signal WTDT remains 0 in the recording period.

If the time constant is too short, the voltage v4 will vary greatly depending on the length of the 00 section of the recording signal WTDT.
The output power when T becomes 1 also varies. On the other hand, if the time constant is too long, the phase delay of the servo system increases, making it difficult to control the output power.

The operation of the semiconductor laser drive circuit of this embodiment configured as described above in accordance with an external signal will be explained using the operation explanatory diagram of FIG.

In FIG. 2, a shows the states of this semiconductor laser drive circuit, including stop and play, respectively.

Indicates the status of recording on a write-once optical disc, playback, recording on a rewritable optical disc, playback, and stop. However, recording on a rewritable optical disc is as follows: erasing section 1 overwriting section, erasing section 3
It consists of two states. Each state is indicated by 1 to 8 in order. b - e are a light emission command signal LDON and a recording gate signal W TGT, respectively.

recording signal WTDT, erasing signal KR (rT timing, f is the output power of the semiconductor laser LD, g is the current source 6
The current X6 of the current generator 3 and current source 9 are shown according to their respective states. The straddling broken line IP is determined by the size of the current work 3 and the current work 5.

This is a curve showing the relationship between the drive current of the semiconductor laser LD and the output power (horizontal axis), and the point ITH is the threshold current. In the following explanation, only the symbols for the b-e signals will be abbreviated.

The operations will be explained below in order from ■.

■ In the stopped state, LDON, WTGT, WTDT.

and KRC,T are all 0. An external control unit (not shown) that generates these signals always outputs WTGT and WTDT when LDON is 0.

and KRGT are set to 0 to prevent unintended signal combinations from occurring. At this time, the first and second servo circuits are in a stopped state, no current flows through the semiconductor laser LD, and the output power is also zero.

■ In the playback state, only LDON becomes 1. Only the first servo circuit serves as a sample state.

Only the electric current 3 flows through the semiconductor laser LD to output reproduction power.

■ In write-once recording mode, in addition to LDON, WTG
T becomes 1. Since WTGT becomes 1, the first servo circuit is not in the hold state, and the current source 6 continues to flow the current 3 corresponding to the reproduction power. On the other hand, the second servo circuit receives WTGT=1 and becomes active. When WTDT input at the same time as WTGT is 1, it is superimposed on the current source 9's 5ft semiconductor laser LD. According to the above-mentioned principle, the output power at this time can be set to the recording power. W
When TDT is 0, the output power becomes the reproduction power. That is, the WTDT modulates the output power of the semiconductor laser LD into recording power and reproduction power.

■ Since WTGT=O, the playback state resumes (same as ■).

(2) In the erase section, the output of the semiconductor laser LD is set to erase power prior to the overwrite section. The first part of the recording (
The purpose is to set the optical disc (on an optical disc) to the same power conditions as during recording. Along with this, it is also used to convert the bias power during recording into erase power. ERGT in the erasure section
Let be 1. Only the first servo circuit works. Switch the target value of the output power from the reproduction power to the erase power while keeping the sample state intact. The output power of the semiconductor laser LD becomes erase power by servo control.

■ In the overwriting section, WTGT is set to 1 in addition to ERGT. As shown in (2), the current value 3 of the current source 6 is fixed at a value corresponding to the erasing power. At the same time, the second servo circuit outputs recording power according to WTDT. Current source 9 outputs current X5 corresponding to the difference between recording power and erasing power.

■ When overwriting is completed, the state is the same as in the - carrier erasure section. This is to ensure that the power conditions at the end of recording are the same as those during recording. The operation is the same as ■.

■ When the recording on the rewritable optical disc is completed, the playback state is resumed. The operation is the same as ■.

■ The operation in the stopped state is the same as ■.

The above recording operation is executed in so-called sector units. When reproducing the address part, the reproduction power is used.

As described above, according to this embodiment, by providing the first current source that sets the read power or erase power and the second current source that sets the recording power, the semiconductor laser is Maximum power and minimum power can be set independently.

Note that in this embodiment, the voltage sources VOFF and VP.

Although WE and VR are independent voltage sources, one 1)-A large converter may be used for both. That is, one D-person converter generates a voltage v1 that determines the target power according to stop, playback, and erasure. This eliminates the need for analog function switches SW1 and SW2. However, a function for determining the stop, playback, or erase state is required before the D-large converter. The voltage vr that determines the recording power also uses the same voltage converter as described above. Since the current source that determines the minimum power during recording is in a hold state, it does not change even if the voltage v1 changes. The output level of the D-person converter is changed to a value corresponding to the recording power in response to the recording gate signal WTGT=1. When the recording gate signal becomes WTGT-0, the original output level is restored.

In addition, in order to stop the emission of light from the semiconductor laser LD, the voltage v1 to the error amplifier 4 is made negative, but other methods such as means for cutting off the current source 6 and forcing the monitor voltage vm to a high level are also available. , any means for stopping light emission may be used.

Furthermore, although the recording gate signal WTGT is used to switch between sample and hold in the sample and hold circuit 5, a separate signal may be provided as long as it has the same purpose.

Although the semiconductor laser LD for driving purposes is shown as having its anode connected to a power source and driving current from the cathode, this connection may be reversed. Furthermore, the light receiving element 2 that monitors the output power of the semiconductor laser LD is not limited to a light receiving element housed in the same package as the semiconductor laser LD as illustrated, but may also be a light receiving element that detects an error signal for tracking, for example. good.

FIG. 3 is a specific example in which the semiconductor laser drive circuit in the embodiment of the present invention is replaced with a specific circuit. In FIG. 3, blocks that are the same as those shown in FIG. 1 are given the same bud numbers and surrounded by a dashed line. This specific example is a circuit that operates with the ground as the maximum potential. A description of the operations between the blocks shown in the embodiment will be omitted, and only the configuration and operation within each block will be shown below.

31L, together with an operational amplifier and a resistor 3b, converts the monitor current Im of the light receiving element 2 for monitoring into a monitor voltage vm.

This voltage increases in the negative direction with reference voltage Vref' as the origin. The product of the resistance value R of the resistor 3b and the monitor current m becomes the monitor voltage vm. 4a is an operational amplifier that constitutes the error amplifier 4. The sample hold circuit 5 has a resistor 5! L
and 5d, capacitors 51L and 50. switch 6C5
and a buffer operational amplifier 5r. resistance 5b
and capacitor 5a are for compensating the phase delay caused by sample-hold resistor 5d and capacitor 5θ. The switch 6C is turned off when the recording gate signal is 1 (high, level). The buffer amplifier 5r is selected to have a small input bias current. Signals from current sources, which will be described later, are fed back to the negative phase input terminal of the buffer amplifier 5f to stabilize the operation. The current sources consist of a transistor 6B, a feedback resistor 6b, and a power supply VXX, and output a current source 3 which is the voltage V 3 (head seen from VEX) output from the sample and hold circuit divided by the resistance value of the resistor 6b. do. The peak hold circuit 7 includes an operational amplifier 7a, an ideal diode in the negative potential direction consisting of a diode, a capacitor 7C that holds this output, and a resistor 7d that provides an appropriate time constant.
Consists of. The error amplifier 8 consists of an operational amplifier 82L, resistors 8b and 8d, and a switch 8C. switch 8c
When is off, the voltage v4 operates so that a feedback signal from the current source 9, which will be described later, and a value obtained by dividing the voltage vr by the resistors 8b and 8d match the voltage v4. When the recording gate signal WTGT is 0 (low level), the switch is turned on, forcing the output of the operational amplifier 8a to a low level, and cutting off the output 5 of the current source 9. The current source 9 is a transistor 92L.

It consists of a resistor 9b and a power supply YXK, and functions almost in the same way as the current source 6. The switch SW3 includes transistors 5W3b and SW3C of a differential configuration that connect the current switch 5 to either the semiconductor laser LD or the ground, and a differential driver that drives each transistor. Recording signal W
It operates to modulate the current generator 6 by the TDT.

As described in detail, according to the present invention, it is possible to realize a semiconductor laser and a drive circuit that can perform one-spot overwriting on a rewritable optical disk and recording on a write-once optical disk with a simple configuration. , its practical effects are great.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a semiconductor laser drive circuit according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the same embodiment, and FIG.
The figure is a circuit diagram showing a specific example of the configuration of the semiconductor laser drive circuit according to the embodiment of the present invention, and FIG. 4 is an explanatory diagram showing the output power of the semiconductor laser necessary for overwriting by one spot. LD... Semiconductor laser, 2... Light receiving element, 5... Sample hold circuit, 7... Peak hold circuit.

Claims (4)

[Claims] (1) A light receiving element that detects the output power of the semiconductor laser as a monitor signal, and a first light receiving element that refers to the monitor signal and applies a current to the semiconductor laser so that the output power of the semiconductor laser becomes a first level. a current source; a second current source that superimposes and causes a current to flow through the semiconductor laser so that the output power of the semiconductor laser becomes a second level higher than the first level with reference to the monitor signal; A semiconductor laser drive circuit comprising: modulation means for modulating the second current source in response to a recording signal. (2) The first current source includes a first reference signal source that outputs a power setting signal for determining erase power or reproduction power depending on the presence or absence of an erase gate signal indicating an erase period; an error amplifier that amplifies the difference between the signal and the signal; a first current output circuit that outputs a current according to the output of the error amplifier; When there is no recording gate signal to indicate, the output of the error amplifier is sampled and transmitted to the first current output circuit so that the power setting signal and the monitor signal match, and the semiconductor laser drive current is servo-controlled; The semiconductor laser drive circuit according to claim 1, further comprising a sample and hold circuit that holds the output of the error amplifier up to that point and keeps the semiconductor laser drive current constant when there is a recording gate. . (3) The second current source includes a second reference signal source that outputs a power setting signal for determining recording power, a peak hold circuit that holds the peak value of the monitor signal, and the second reference signal source. a second current output circuit that outputs a current by weighting the output current of the first current source by servo control so that the output of the peak hold circuit matches the output of the peak hold circuit; 2. The semiconductor laser drive circuit according to claim 1, further comprising a control circuit for stopping the current output of the second current output circuit. (4) The semiconductor laser drive circuit according to claim 1, wherein the first reference signal source and the second reference signal source can each independently change the level of the power setting signal by an external signal.