JPS6032145A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To eliminate the temperature effect of current-optical output characteristics by using a laser current control means which detects the intensity of the output light of a semiconductor laser to obtain a prescribed low level and a constant current control means of a laser drive modulating element which obtains a prescribed high level. CONSTITUTION:A photodetector 3 is set in proximity to a semiconductor laser 1 to detect the intensity of the output light. The outputs of monostable multivibrators 14 and 15 which work by the fall and rise of a record pulse P are supplied to sample and/hold circuits 16 and 17 respectively. The outputs of circuits 16 and 17 are supplied to comparators 18 and 19 and compared with the prescribed reference value. The output of the comparator 18 controls a current control transistor TD1 so that the optical output of the laser 1 is kept at a fixed reproduction level when the pulse P is not irradiated. The output of the comparator 19 controls the current of a constant current circuit 20 which is set in series to a switching transistor TR3 for modulation which drives the laser 1 in response to the pulse P. Thus it is possible to eliminate the effect of variation in current- optical output characteristics due to temperatures.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser drive circuit in an optical information recording/reproducing device using a semiconductor laser as a light source.

Prior Art FIG. 1 shows a general groove configuration of an optical pickup in an optical information recording/reproducing apparatus.
As a result, the laser beam emitted from the semiconductor laser 1 is made into parallel light by the collimator lens 2, reflected by the polarizing beam splitter 3, and passed through the 1/4 wavelength plate 4. It becomes polarized light, and the objective lens 5
The light is focused on the optical recording medium 6 on the surface of the disk 7, and recording is performed by forming pits. In addition, during reproduction, the output of the semiconductor laser 1 is weakened in the semiconductor laser drive circuit 12, and the laser beam is focused on the surface of the disk 7 through the entire optical system. The 174 wave layer 4 is linearly polarized light with a phase shift of 90'' from the irradiation time from Yamanaka rμf, and the reproduced information is obtained by detecting the linearly polarized light.In addition, the linearly polarized light is The light passes through the splitter 3, passes through the entire lens 8, and is guided to the focus servo detector 11 and the i-tracking servo detector 10 by the nozzle mirror 9, whereby each servo is detected. - In such an optical information recording/reproducing device, recorded information is recorded on the disk 7 in the form of a digital signal series.Therefore, the laser beam output of the semiconductor laser 1 is almost binary in accordance with the recording pulse P. Even when recording pulses are not being applied, a laser beam with a weak output must be emitted to perform focus and track detection, just as it is during playback.The laser light output during recording is equal to that during playback. The information on the disk 7 is recorded as uneven pits by melting and removing the optical recording medium 6 with a strong beam during recording.The situation at that time - Fig. 2 1 in the figure.
)1 indicates the recording level t'', pz indicates the reproduction level, and pl is set to about 10 times pz.

Conventionally, when driving the semiconductor laser 1 in such an optical information recording/reproducing apparatus, the laser output is kept at the reproduction level except when the entire recording pulse is irradiated during the recording operation (see FIG. 2).

However, if such a measure is taken, step 5 shown in Fig. 3 will result.
If the differential member efficiency of the semiconductor laser 1 changes with temperature, the slope of the current-optical output IF characteristic may change, which causes the optical output of the semiconductor laser 1 to fluctuate during recording pulse irradiation. , it becomes impossible to form all pits with the correct shape, i.e.,
In FIG. 3, II, I2. Even if the value of I3 is controlled and the amplitude A of the control pulse is kept constant, the optical output level during recording pulse irradiation at temperature T2 will vary from pz to p't compared to the case of 'ro, 'r. It becomes VC that it decreases to.

Purpose The present invention has been made in consideration of the above points, and has an object to enable stable and accurate information recording at all times without being affected by fluctuations in current-light output characteristics due to temperature of a semiconductor laser. The present invention provides a semiconductor laser drive circuit for an optical information recording/reproducing device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

In the semiconductor laser drive circuit according to the present invention, as shown in FIG. Sample and hold circuits 16 and 17 sample and hold the output of the photodetector 13 as a sampling pulse for each output of the monostable multivibrator 14 that operates and the monostable multivibrator 15 that operates at the rising edge of the monostable multivibrator 14, and their respective sample and hold circuits. Output voltage 111!VF1x* Vsz
A current is provided to maintain the optical output of the semiconductor laser 1 at a constant reproduction level except when recording pulses are irradiated, based on the outputs of the comparators 18 and 19, which compare the k reference set values Vreft and Vrefz, respectively, and the comparer 18. A control transistor T'rs and a modulation switching transistor T that drives the semiconductor laser 1 according to the recording pulse P.
A constant current circuit 20 is provided in series with r3, and current control in the constant current circuit 20 is performed based on the output of the comparator 19 to record the optical output of the semiconductor laser 1 at a constant level and keep it within a certain limit during recording pulse irradiation. A current control transistor 'I'rz constitutes a current control transistor 'I'rz.

The operation of the semiconductor laser drive circuit according to the present invention configured as described above will be explained below.

The detection output a of the photodetector 13 is given to sample and hold circuits 16 and 17, respectively, where the recording pulse P
The sampling pulse (lb*cic) is sampled and held in synchronization with the falling and rising edges of . Therefore, the output d of the sample hold circuit 16 corresponds to fluctuations in the optical output of the semiconductor laser 1 which is at the reproduction level except when the recording pulse is irradiated. , and the output e of the sample hold circuit 17 shows the fluctuation of the optical output of the semiconductor laser 1 during recording pulse irradiation.A time chart of each section 18 is shown in FIG.

First, the rJI+ operation when maintaining the optical output of the semiconductor laser 1 at a constant reproduction level except during recording pulse irradiation will be described.

That is, the output d (voltage value VSI) of the sample and hold circuit 16 is given to the comparator 1B, where it is compared with a reference value Vrefs set according to the reproduction level, and the current control open transistor is selected according to the difference output v1. 1'
r1 is driven accordingly. At this time, the current control transistor Trr operates once at J:5 when the semiconductor laser IVC supplies il given by the following equation.

R.

As shown in FIG. 6, if the current-light output characteristics change from temperature T1 to T2, the original IM,
The optical output for the current is from pt (reproduction level) to p
′l. Therefore, the voltage VSI of the output d of the sample and hold circuit 16 tries to increase as shown in FIG.
Since negative feedback is applied so that St is equal to the reference voltage Vreft, the output vl of the comparator +8 is equal to Vat.
=Vrefx. According to the relationship of equation (1) in III, the current i1 is reduced to 1'1 in FIG. 6, and the optical output is controlled to be ps. In other words, even if the current-optical output characteristics change, the optical output of the semiconductor laser 1 other than when irradiating the recording pulse is always maintained at the playback level p. Next, when irradiating the recording pulse, the optical output of the semiconductor laser 1 The operation when holding the optical output of 1 at a constant recording level will be explained. In other words, the output e (voltage value v82) of the sample and hold circuit 17 is given to the comparator 19, where it is set according to the recording level. It is compared with the base 11Al1i-Vref2, and the current limiting transistor Tr2 is appropriately driven according to the difference output v2. At that time, 'tK style 11i
The transistor Tr2 for 11111tl is supplied to one transistor Tr6 in the current '+f constant current circuit 2o given by the following equation.

2 At this time, since the modulation switching transistor Tr3 is on, the other transistor 'I'rs in the mouse current circuit 20 operates to supply the current 12 to the semiconductor laser 1. Therefore, as shown in FIG. 6, when the temperature changes from T1 to T2vcK, the output v1 of the comparator 18 becomes VEL, which is completely similar to the case described above.
l = 'Vreft K11 down by one degree and V
(, the output v2 of the ratio 'iffer t9 is v82 = Vref
z, and then ↓niJ Ffe (1
)v From the relationship in equation (2), the 1-pressure flow i3 supplied to the semiconductor laser 1 is reduced to 0'3 in FIG. 6, and the optical output is immediately maintained at the recording level p2.

In addition, since the switching transistor Tr3 of VC is turned off except during recording pulse irradiation, the other switching transistor Tr5 of the military main circuit 2° is
4? I! 1 current is supplied to the tube 2, and the semiconductor laser 1 is no longer supplied with the current jxL.

1. C. In the above explanation, we have described the case of recording and reproducing information on an optical disk, but the present invention can be widely applied to other devices in which information is recorded using the intensity of a laser beam. Needless to say, it can be done. As for the means for sampling and holding the output of the photodetector, it is sufficient if the optical output of each semiconductor laser can be measured at the time of recording pulse irradiation and at the reproduction level, and in addition, for example, the peak An error using a bold circuit may also be used.

As described above, the semi-integrated laser driving circuit according to the present invention includes a photodetector that emits the intensity ktrQ of the output light of the semiconductor laser, and a semiconductor laser that is at a weak level based on the output of the photodetector Q. A first means for holding the output, a second means for holding the semiconductor laser output which is also at a strong level, and a Philippine-Chinese exchange between the hold output of the first means and the weak level The difference output between the first comparator that compares the hold output of the second means with the strong level reference I, and the first comparator becomes zero. AUf in semiconductor laser
A first current control means for supplying Af, a redundant current circuit provided in series with a modulation element for driving a semiconductor laser in accordance with a recording pulse, and a differential output of the second comparator is zero. A second torrent flow control circuit is used to control the torrent current of the constant current circuit so that
During intermittent IJ operation, the optical output level of the semiconductor laser at 9 or 10 degrees is always kept constant without being affected by the main fluctuations (particularly the fluctuations in slope) of the semiconductor laser's current-light output due to temperature changes, etc. It has five distinct advantages, such as being able to perform stable recording and reproduction in the original i-M information recording and reproducing apparatus.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of the original pickup in a general optical information recording/reproducing device, Fig. 2 is a diagram showing the optical output of the semiconductor laser at symbol time and the recording state on the disk, and Fig. 3 is a diagram showing the conventional semiconductor laser. FIG. 4 is an electrical connection diagram showing an embodiment of the semiconductor laser drive circuit according to the present invention; FIG.
The figure is a time chart of each part signal in the same embodiment, No. 6
The figure is a diagram showing the current -)f: and output characteristics in the case of the same embodiment. 1... Semiconductor laser 13... Photodetector 1
4゜15... Monostable multivibrator 16.17
...Sample hold circuit 18.19...Comparator 20...Constant current circuit Tr b Tr 2...Current control transistor Tr3...Switching transistor (modulation element) Applicant's agent Kiyoshi Torii Figure 1 Figure 2 0 ------------- Figure 3 AA Figure 5 0 -------------- Temporarily open □ Figure 6

Claims (1)

[Claims] a photodetector that detects the intensity of the emitted light from the semiconductor laser; a tenth flat film that holds the semiconductor laser output at a weak level based on the detected output; and a second flat film that also holds the semiconductor laser output that is at a strong level. means, a first comparator for making a ratio v1 between the hold output of the first means and the weak level reference value, and a first comparator for comparing the hold output of the second means with the strong level reference value. a first current control means 111 for supplying the first current to the semiconductor laser in the second comparator and the first current comparator 5 in which the difference output between the first and second comparators becomes zero;
The current of the constant current circuit is controlled so that the difference output between the second comparator (-1) and the second comparator (-1) is zero. The second current control means is connected to the second current control means. 44q
v-flat;rtlk+ノ aum7J+l+1FILI&