JPH01140433A - Laser driving circuit - Google Patents

Abstract

PURPOSE:To accurately switch a laser output either from reproducing to recording or from the recording to the reproducing at a high speed with simple composition by driving a laser device using a laser driving current either for the recording or for the reproducing in accordance with recording information at the time of the recording and driving the laser device using the laser driving current for the reproducing at the time of the reproducing. CONSTITUTION:A recording pulse control means 21 is provided which synthesizes a binary current signal IDT in accordance with the recording information to a laser driving current IL in accordance with reference voltage VWRITE for the recording and generates a first laser driving current IL1 in accordance with the reference voltage VWRITE for the recording and a second laser driving current IL2 in accordance with reference voltage VREAD for the reproducing. Thereafter, by controlling the binary current signal IDT, the recording pulse control means 21 drives a laser device 4 using either the first laser driving current or the second laser driving current IL1 or IL2 corresponding to the recording information at the time of the recording and using the second laser driving current IL2 at the time of the reproducing. Thus, either the recording or the reproducing can be controlled without switching reference voltage VREF of an automatic power control circuit.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A: Industrial field of application B: Outline of the invention C: Prior art (Figs. 3 and 4) D: Problems to be solved by the invention (Figs. 3 to 8) E: Means for solving the problems (Fig. 1) F action (1st
Figure) G Embodiment (Figures 1 and 2) H Effects of the Invention A Industrial Application Field The present invention relates to a laser drive circuit, and is used, for example, when recording or reproducing recorded information on an optical disk in an optical disc device. It can be applied to those that drive the laser diode used.

B Summary of the Invention The present invention is a laser drive circuit having an automatic power control circuit configuration, in which a binary current signal is synthesized in accordance with recording information with respect to a laser drive current obtained using a recording reference voltage as a reference voltage. generates a recording laser drive current and a reproduction laser drive current, controls the binary current signal, uses the recording or reproduction laser drive current during recording, and uses the reproduction laser drive current during reproduction. By driving the laser device using the drive current, recording or reproducing operations can be controlled without switching the reference voltage of the automatic power control circuit.

C. Conventional technology Conventionally, laser diodes used in optical heads of optical disk devices, etc. have large output fluctuations due to changes in ambient temperature, etc., so a monitoring photodiode, etc. built into the laser device is used to control the laser output. What is the so-called automatic power system? il (A
P C (automatic4cpower control
l)) A laser drive circuit having a circuit configuration is used.

That is, the laser drive circuit 1, as shown in FIG.
IEAll or Vwm+tt) is input to the positive input terminal of the subtraction circuit 3 via the recording/reproduction changeover switch circuit 2 whose switching is controlled by the recording/reproduction changeover signal SIIIM.

A monitor current ■ obtained from a photodiode PD built into the laser device 4 is connected to the negative input terminal of the subtraction circuit 3 . but,
The current-voltage conversion amplifier circuit 5 converts it into a monitor voltage V, and this monitor voltage vM is passed through a low-pass filter circuit (LP
F) is input via 6. As a result, the subtraction circuit 3
By controlling the amplifier circuit 7 using the subtraction result obtained from the subtraction result, a driving voltage VL is generated according to the difference between the reference voltage V□ and the monitor voltage v,4.

The drive voltage vL obtained from the amplifier circuit 7 is supplied to the voltage-to-current conversion amplifier circuit 9 via the variable characteristic loop filter 8, and the drive current obtained thereby! , the addition circuit 10
By supplying the reference voltage V READ or VW for reproduction or recording to the laser diode LD in the laser device 4, the APC circuit is constructed as a whole.
III! It is possible to stably send out a laser output P (PIIEAD or P.17.) corresponding to the

In addition, in FIG. 4, when the servo characteristics of the laser drive circuit 1 are stable, the gain of the amplifier circuit 7 is K, the gain of the voltage-current conversion amplifier circuit 9 is 1 and KL on the input and output sides, respectively.
Furthermore, response characteristics to a unit step function are shown when the gain of the current-voltage conversion amplifier circuit 5 is 1, and the frequency characteristics of the variable characteristic loop filter 8 and LPF 6 are ω7 and ω3, respectively.

Here, using this laser drive circuit 1, an optical disc (
When recording predetermined data on the upper recording track (not shown), the recording reference voltage V is set as the reference voltage V REF.
W□A is selected, and a recording pulse P- having a binary level consisting of a 0 level according to the recording data and a current level that is an inversion of the current value according to the recording reference voltage V□1A. is supplied to the adder circuit 10 to control the laser diode LD on and off according to the recorded data,
This allows desired recording data to be recorded on the optical disc.

By the way, in practice, when recording data on an optical disk, prior to that, the reference voltage VIIf for reproduction is set.
Using the AD, a laser diode LD sends out a laser beam for reproduction, thereby reading information such as tracks and sectors preformatted on the optical disk.
At the timing when a predetermined address is detected, the recording/reproduction changeover switch circuit 2 is used to switch the reference voltage □ to the recording reference voltage vw+u'rt.
The response characteristic to the laser output P during this transition period is expressed by the following formula K
K+KL('+Jt(s+ω,) X VlKF ・”=
(1), and on the other hand, the response characteristic of the recording pulse frequency to the laser output P is expressed as ×PAc... (2) (PAc is the laser output corresponding to the recording pulse P).

Here, in equation (1), the response characteristic when switching from the reproduction reference voltage V□1 to the recording reference voltage vwm+tt is as shown in FIG. 5(A) when using the variable characteristic loop filter 8. The characteristic curve TI corresponds to the constant ω1.

On the other hand, in equation (2), the time constant ω of LPF6
3, during recording pulse drive, in order to smooth the monitor voltage v, 4, a time constant higher than the time constant ω1 of the variable characteristic loop filter 8 is selected, and as a result, its frequency characteristics are as shown in FIG. As shown in (A), the recording pulse Pwl has a differential characteristic and the frequency ω. The part corresponding to is assumed to have a flat characteristic.

D Problems to be Solved by the Invention By the way, in the laser drive circuit 1 having such a configuration, the reproduction reference voltage vttAo is changed from the recording reference voltage V□I□.
It can be seen that in order to make the response characteristics faster when switching to (that is, to make the rise of the recording laser output faster), the time constant G of the variable characteristic loop filter 8 should be made larger. Incidentally, if you do this, the fifth
The characteristic curve Tl described above for figure (A) has a time constant ω1
The characteristic curve T10 (FIG. 5(B)) rises at the position.

However, on the other hand, if the time constant ω1 of the variable characteristic loop filter 8 is increased, the frequency characteristic during recording pulse driving becomes the frequency ω of the recording pulse P□, as shown in FIG. 6(B). enters the differential region, which results in Figure 7 (A)
For the recording pulse P□ with the pulse waveform shown in
There is a possibility that distortion as shown in FIG. 7(B) may occur in the pulsed light of the laser output P.

Furthermore, in addition to this, the Q of the frequency characteristic becomes high (and the damping amount is insufficient), so that the reference voltage V□7 is changed from the reference voltage for reproduction to the recording reference voltage as shown in Fig. Immediately after switching to the reference voltage VWIII!, an overshoot operation as shown in FIG. 8(B) occurs, which may destroy the laser diode LD.

Therefore, in the conventional laser drive circuit 1, the time constant ω1 of the variable characteristic loop filter 8 is increased only for a predetermined period at the timing of switching from the reproduction reference voltage VltAfl to the recording reference voltage V□, . Those designed to do so are used.

That is, this variable characteristic type loop filter 8 supplies the driving voltage vL obtained from the amplifier circuit 7 to the voltage-current converting amplifier circuit 9 through the resistor R1, and also connects the loop filter 8, which has one end grounded. In addition to this, an amplifier circuit 8B having an operational amplifier configuration is connected to the first input terminal a of the switch circuit 8A and is negatively fed back to the capacitor C6 of the switch circuit 8A.
is supplied to the second input terminal of the switch circuit 8A.

Furthermore, the output end of this switch circuit 8A is grounded via the second capacitor C2, and the second input end is grounded only during the rising period of the recording/reproduction switching pulse signal PRW input to the switch control end. You are given a choice.

Here, the recording/reproduction switching pulse signal P□ is obtained by inputting the recording/reproduction switching signal 5IIW input to the recording/reproduction switching circuit 2 via, for example, a differentiating circuit (not shown).
As a result, the reference voltage for recording VWIIl? is changed from the reference voltage for reproduction VIIEAD. Only during a predetermined period when switching to E, the time constant ω of the variable characteristic loop filter 80 is changed from the value ω, = 1/(C, +C,)R] to the value ω+ = 1.
/ C, R1.

However, even with this method, the reference voltage for reproduction V R
During the period when the EAD is switched to the recording reference voltage V, a certain amount of time is required to stably control the laser output P due to problems such as the distortion described above. However, on the optical disk, a blank area is required between the reproduction area and the recording area, which inevitably leads to a decrease in the overall recording density, which is still insufficient as a solution.

The present invention has been made in consideration of the above points, and provides a laser drive circuit that solves the problems of conventional laser drive circuits at once and can control a laser device from a reproduction state to a recording state at high speed and accurately. This is what I am trying to propose.

E Means for Solving Problem E In order to solve this problem, in the present invention, the laser output P emitted from the laser device 4 is outputted, and the detected output VH is set to a predetermined standard for recording or reproducing. Voltage■
□y (v□lft or V□.) and controls the laser drive current IL based on the comparison result to stabilize the laser output P emitted from the laser device 4 according to recording or reproduction. In the laser drive circuit 20 having an automatic power control circuit, the recording reference voltage (1) is set. ,7. Laser drive current according to! , is synthesized with a binary current signal ■ゎ according to the recording information, and a reference voltage for recording VWIIIT is obtained.
! The first laser drive current ILI and the reference voltage for reproduction Vll! . The second laser drive current ILZ according to
By controlling the binary current signal EDT, the first or second laser drive current ILI or ILZ is set in accordance with the recording information during recording.
The laser device 4 is driven using the second laser drive current Ill during reproduction.

6. Control the binary current signal rot to drive the laser device 4 using the recording or reproducing laser drive current ILI or rLz during recording and using the reproducing laser drive current rLz during reproduction. As a result, the recording or reproducing operation can be controlled without switching the reference voltage 1F of the automatic power control circuit.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. Instead of adding the recording pulse P □ over the recording laser drive current domain, depending on the recording pulse rot input in the recording pulse control circuit 21,
By controlling the drive current (1) supplied from the voltage-current conversion amplifier circuit 9 to the laser diode LD, it is possible to irradiate the optical disk with laser light that can form recording pits according to recorded data. .

That is, in the recording pulse control circuit 21, the input recording pulse lot is applied to the base of the switching transistor Q1 via the buffer circuit 22. Further, the collector of the transistor Ql is connected to the laser diode LD, and the emitter is grounded via a resistor R2.

A note on this! During the period in which the level of the pulse I0A is low, the transistor Q1 is turned off, so that the entire drive current I given to the laser diode LD by the voltage-current conversion circuit 9 is reduced.
During the period when LI is supplied and the recording pulse 11 is at a high level, the transistor Q1 is turned on, so that the drive current IL flows through the resistor R2 connected to the emitter of the transistor Q1 and the laser diode LD.
is shunted by the internal resistance of the laser diode L
A drive current IL□, which is a part of the drive current [L, is supplied to D.

In the case of this embodiment, the resistance value of the resistor R2 is smaller than the internal resistance of the laser diode LD during recording (that is, as the reference voltage V RtF, the recording reference voltage VwRMr
E is set) and the transistor Q1 is turned on, the reference voltage V for recording. The drive current I corresponding to □T is shunted and the drive current rt corresponding to the reproduction reference voltage □0 is applied to the laser diode LD.
The ratio is selected such that it can supply z.

In this manner, when the laser drive circuit 20 as a whole reproduces a recording track on an optical disk, the reference voltage for reproduction VIIEAD is used as the reference voltage V□, and the laser beam consisting of the laser output for reproduction P READ is used. Irradiate onto the optical disc.

Conversely, when recording data on an optical disk, the reference voltage □ is set to the recording reference voltage VWIII.
By generating the drive current IL using □E and controlling this drive current □ using the recording pulse control circuit 21, the recording pulse I is generated. During the period when writing is required on the optical disk according to T, the laser output for recording P□1
7t and during a period when no writing is required, the reproduction laser output P IIEAD can be used to record the recording data according to the recording pulse on the optical disk, and when performing the reproduction operation necessary for the recording operation, By controlling the recording pulse IDT and keeping it at a high level, the reference voltage V
□, the laser output for reproduction P IIEAD which is made of continuous light without switching to the reference voltage V IIEAD for reproduction
It is made to obtain.

In the above configuration, for example, when recording data on a sector SEC (FIG. 2(A)) of a predetermined recording track among a plurality of recording tracks TR formed concentrically on an optical disk, first The reference voltage V*tj of the laser drive circuit 20 is set to the reproduction reference voltage VIIIA (FIG. 2(B)), and the sector information IDs is preformatted on the recording track TR. , and search for the desired sector SEC.

In the case of this embodiment, for example, 50 sectors SEC are arranged on one round of one recording track of the optical disc.
Each sector SEC has a sector information area ID including a track number, sector number, update information, etc. at the beginning! EC is arranged, and the data area DT following it is
It is divided into, for example, 20 small sectors 5SEC each having a synchronization area SY and a servo area SB at the beginning.

When a desired sector SEC is detected by reproducing the track number and sector number at time t, for example, among the sector information tI)stc being reproduced, the reference voltage v-1 is reproduced in order to update the update information. Reference voltage V II
Reference voltage for recording from EAD■□37. ■ Switch to the prescribed recording pulse. 7 (FIG. 2(C)) to the recording pulse control circuit 21, various information such as update date and time is recorded as update information.

Next, in the conventional laser drive circuit 1, the reference voltages ■, , , are switched again to the reference voltage VIIEAD for reproduction, and the synchronization area SY arranged at the beginning of the small sector 5SEC is
and the servo area SB, and further the reference voltage V R
IF is the reference voltage for recording VWl14! However, in the laser drive circuit 20 of the present invention, the reference voltage V RlF is changed to the recording base 31# voltage V14m.
1T! Recording pulse 1. By maintaining a predetermined level, a laser beam for reproduction is irradiated onto the optical disk, and the synchronization area SY and servo area SB arranged at the beginning of each small sector 5SEC are reproduced. By controlling the recording pulse IDT according to the recording data, predetermined recording data can be recorded in the data area DT of each small sector 5 SEC.

Thus, the entire laser drive circuit 20 has a reference voltage V
By minimizing the switching of REF to a practical minimum, this reference voltage V
In addition to preventing waveform distortion caused by the influence of the response characteristics of the APC circuit and damage to the laser diode LD due to drive current overshoot when switching between By doing this, the speed is significantly increased and blank areas do not occur on the recording track.

According to the above configuration, in the laser drive circuit 20 made of an APC circuit, the reference voltage for recording is set at the time of data recording.

Drive current according to R10, recording pulse control circuit 2
1 to generate a recording drive current ILI or a reproduction drive current rLz, and a recording laser output P during a period in which writing is required according to recording data. 1A, and laser output P□ for reproduction during a period when writing is not required. When irradiating the optical disc onto the optical disc and performing a predetermined reproducing operation necessary for recording, the reproducing laser output P IIEAD
By using this, it is possible to minimize the switching of the reference voltage V REF in response to recording and playback operations, and as a result, due to the response characteristics of the APC circuit, the laser radiation generated due to the switching of the reference voltage can be minimized. By eliminating output distortion and quickly and accurately switching the laser output from playback to recording or from recording to playback, it is also possible to eliminate blank areas on optical disks, thereby improving the efficiency of use of optical disks. A laser drive circuit can be realized.

Furthermore, according to the above-described embodiment, since there is no need to instantaneously switch the time constant of the loop filter, the variable characteristic loop filter 8 is simply configured as a low-pass filter, and furthermore, generation of the recording/reproducing switching pulse PRw, etc. By eliminating the need for this, a laser drive circuit with an overall simple configuration can be realized.

Note that in the above embodiment, when playing back an optical disc,
Although the reference voltage for reproduction is used as the reference voltage, instead of this, only the reference voltage for recording may be used as the reference voltage, and the laser output for recording or reproduction may be controlled by the recording pulse. good.

Further, in the above embodiment, the APC circuit receives the laser beam emitted backward from the laser beam irradiated onto the optical disk side, but the present invention is not limited to this, and the optical path from the laser diode to the optical disk is It can also be applied to a so-called front monitor type APC circuit in which a half mirror or the like is inserted to monitor laser light.

Further, in the above-described embodiment, a case was described in which the laser drive circuit according to the present invention was applied to an optical disk device, but the present invention is not limited to this, and may be applied to other optical recording media such as an optical tape or an optical card. The present invention can be widely applied to laser drive circuits that record or reproduce data in optical information recording/reproducing devices.

H Effects of the Invention As described above, according to the present invention, in a laser drive circuit having an automatic power control circuit configuration, a recording reference voltage is used as a reference voltage to obtain a laser drive current, and a recording pulse control means is used to obtain this laser drive current. A binary current signal consisting of control information including recording information is synthesized with the laser drive current to generate a laser drive current for recording and reproduction, and during recording, the laser is driven for recording or reproduction according to the recording information. By using current to drive the laser device and using the laser drive current for playback during playback, the laser output can be quickly and accurately switched from playback to recording or from recording to playback with a simple configuration. A laser drive circuit can be realized.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform diagram showing its operation, Fig. 3 is a block diagram showing a conventional laser drive circuit, and Fig. 4 shows its response characteristics. Block diagram, Figure 5 is a characteristic curve diagram showing the frequency characteristics of the laser output with respect to the reference voltage, Figure 6 is a characteristic curve diagram showing the frequency characteristics of the laser output with respect to the recording pulse, and Figure 7 is the relationship between the recording pulse and the laser output. FIG. 8 is a characteristic curve diagram showing the relationship between reference voltage and laser output. l, 20... Laser drive circuit, 2...
Recording/reproduction changeover switch circuit, 3...subtraction circuit,
4... Laser device, 5... Current voltage conversion amplifier circuit, 6... Low pass filter circuit, 7
......Amplification circuit, 8...Variable characteristic loop filter, 9...Voltage-current conversion amplifier circuit, I
O... Addition circuit, 21... Recording pulse control circuit.

Claims (1)

[Claims] The laser output emitted from the laser device is detected, the detected output is compared with a predetermined reference voltage for recording or reproduction, and the laser drive current is controlled based on the comparison result, In a laser drive circuit having an automatic power control circuit that stabilizes the laser output emitted from the laser device according to recording or reproduction, the laser drive current is adjusted according to the recording information in accordance with the recording reference voltage. Recording pulse control means for synthesizing binary current signals to generate a first laser drive current corresponding to the recording reference voltage and a second laser drive current corresponding to the reproduction reference voltage, By controlling the binary current signal, the laser device uses the first or second laser drive current during recording in accordance with the recorded information, and uses the second laser drive current during playback. A laser drive circuit characterized in that it drives a laser.