JPS63251945A - Light source driving circuit - Google Patents

Abstract

PURPOSE:To prevent formation of a it by a bottom level so as to improve the S/N, by releasing the superposition of high-frequency signals of a light source and making the level of a bias driving current lower than that of the reproducing time at the time of recording. CONSTITUTION:A light source 9 which generates prescribed light, a 1st current feeding circuit which supplies a 1st driving current to the light source 19 at the time of the recording mode and reproducing mode, a 2nd current feeding circuit which supplies a 2nd driving current which changes in corresponding to recording signals at the time of the recording mode, with the 2nd current being superposed upon the 1st current, a 3rd current feeding circuit which supplies a 3rd driving current under a condition where the 3rd current is superposed upon the 1st current at the time of reproducing mode, and a generating circuit 20 which generates high-frequency signals to be supplied at the time of the reproducing mode are provided. At the time of the recording mode, modulated 2nd driving current is supplied in state where the 2nd current is superposed upon the 1st current and, at the time of the reproducing mode, the 3rd driving current is supplied in condition where the 3rd current is added to the 1st current and high-frequency signals are superposed. Therefore, the bottom level of the output of the light source at the time of recording can be made equivalent to or lower than the level of the reproducing time and, as a result, the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light source drive circuit suitable for driving a light source such as a semiconductor laser.

[Summary of the invention]

In the present invention, during recording, the superimposition of the high frequency signal of the light source is canceled, and the level of the bias drive current is made smaller than during reproduction.

[Conventional technology]

FIG. 3 is a block diagram of a light source driving circuit for driving a light source used in a pickup of a conventional optical disk device. When reproducing information recorded on an optical disc, both switches 2 and 3 are turned on. The APC circuit 1 monitors the output of a semiconductor laser 19 as a light source, compares the monitor output with a predetermined reference value, and outputs an error signal. This error signal is inputted via a switch 2 to a hold circuit 6 having an operational amplifier 4 and a capacitor 5. The output voltage of the hold circuit 6 is input to a voltage-current conversion circuit 34 made up of an operational amplifier 23, an NPN transistor 24, and a resistor 25, and is converted into a current.

The output of the voltage-current conversion circuit 34 is input to a current mirror circuit 31 as a supply circuit consisting of a resistor 7.8 and a PNP transistor 13.14. Current mirror circuit 31
is the drive current of the transistor 1 corresponding to the signal input from the voltage-current conversion circuit 34 (hold circuit 6).
Output from collector 4. This drive current is supplied to the semiconductor laser 19, and the semiconductor laser 19 outputs laser light at a predetermined level.

Since the output light is monitored by the APC circuit 1 as described above, the output level of the semiconductor laser 19 is controlled to correspond to a predetermined reference value.

On the other hand, a high frequency signal outputted by the generation circuit 20 during reproduction is superimposed on the semiconductor laser 19 via the switch 3 (and a capacitor, not shown, if necessary).

As a result, recorded information can be reproduced without being affected by noise caused by return light from the disc.

The input/output characteristics of the semiconductor laser 19 are shown by the solid line in FIG. Accordingly, output light at the level of Pl is emitted in response to the drive current (2) supplied from the transistor 14.

When recording information on an optical disk, the switch 3 is used to prevent a current exceeding the rated value from being supplied to the semiconductor laser 19.
is turned off. Therefore, high frequency signals are not superimposed. At this time, the switch 2 is also turned off, so the level of drive current during playback is stored (held) in the capacitor 5, and the transistor 14 supplies the same level of drive current as during playback to the semiconductor laser 19. do.

Resistance 11.12. Terminal 21 of a current mirror circuit 32 as a supply circuit consisting of PNP transistors 17 and 18
A predetermined control signal for setting the level of the drive current during recording is input to the. The drive current I3 output from the current mirror circuit 32 is input to a differential circuit 33 consisting of a resistor 9.10 and a PNP transistor 15.16. Since a recording signal is supplied to the base of one transistor 16 of the differential circuit 33, a drive current is supplied from the collector of the other transistor 15 in response to the recording signal.

is output. This drive current I is supplied to the semiconductor laser 19. As a result, the semiconductor laser 19 has a current factor x (=Il+I3) which is the sum of the driving current factor □ and the driving current factor.
) flows. As shown in FIG. 4, when the drive current I2 is input, the output level of the semiconductor laser 19 becomes P2. Eventually, the output of the semiconductor laser 19 changes between the bottom level P8 and the top level P2 in accordance with the recording signal.

On the optical disc, pits are not formed (information is recorded) at the bottom level P□, but pits are formed (information is recorded) at the larger top level P.

[Problem that the invention seeks to solve]

However, the characteristics shown by the solid line in FIG. 4 are those when a high frequency signal is superimposed to reduce the influence of returned light, and the characteristics when no high frequency signal is superimposed are shown by the broken line. As a result, the bottom level at the time of recording is not P, but a higher P. Therefore, in the worst case, pits may be formed even at the bottom level P. Further, since noise is generally likely to occur near the bottom level P, there is a drawback that the S/N ratio becomes poor.

Therefore, the present invention aims to prevent pits from being formed at the bottom level and improve the S/N ratio.

[Means for solving problems]

The present invention relates to a light source drive circuit, which includes a light source that generates a predetermined light, a first supply circuit that supplies a first drive current to the light source in recording mode and playback mode, and a first supply circuit that supplies a first drive current to the light source in recording mode and in response to a recording signal in recording mode. a second supply circuit that superimposes a changing second drive current on the first drive current and supplies the same to the light source; and a third drive current that superimposes the first drive current on the first drive current and supplies the same to the light source in a playback mode. It is characterized by comprising a third supply circuit and a generation circuit that generates a high frequency signal to be supplied to the light source in the reproduction mode.

[Operation] The light source generates a predetermined light. This light source is supplied with drive currents output from three supply circuits and high frequency signals output from a generation circuit. In the recording mode, the second drive l! is modulated by the recording signal. The lI current is supplied superimposed on the first drive current.

In the reproduction mode, the first drive current and the third drive current are added and supplied, and a high frequency signal is superimposed.

〔Example〕

FIG. 1 is a block diagram of a light source driving circuit according to the present invention, and parts corresponding to those in FIG. 3 are given the same reference numerals. In the present invention, the output of a current mirror circuit (constant current circuit) 51 as a supply circuit consisting of a resistor 43.44, a PNP transistor 47.48, and a terminal 49 is supplied from a resistor 41.42, a PNP transistor 45.46, and a terminal 5o. The signal is supplied to the semiconductor laser 19 via a differential circuit 52 . The other configurations are the same as in FIG. 3.

Switch 2 is turned on in playback mode. Therefore, a drive current (constant current) is supplied from the current mirror circuit (constant current circuit) 31 to the semiconductor laser 19. However, this drive current is set to a value ■4, which is smaller than the above case (I□).

Further, in the reproduction mode, a high level control signal is input to the terminal 50, and a control signal is input to the terminal 49 so that the output current of the current mirror circuit 51 becomes Is. As a result, transistor 46 is turned off.

The transistor 45 turns on and the current mirror circuit 51
A drive current (constant current) I5 outputted from the transistor 45 is supplied to the semiconductor laser 19 via the transistor 45.

In the end, the semiconductor laser 19 is supplied with a drive current I (=I, +I,) which is the sum of the drive current I and the drive current I.

As in the case described above, switch 3 is turned on during playback mode, so a high frequency signal is transmitted (via a capacitor not shown).
It is superimposed on the semiconductor laser 19.

As a result, the characteristics of the semiconductor laser 19 become as shown by the solid line in FIG. 2, and its output level becomes P.

The reference voltage of the APC circuit 1 is set smaller than in the above case, corresponding to the drive current. Although automatic level control by the APC circuit 1 is not performed on the component of the drive current T5, it is possible to control the output level of the semiconductor laser 19 to approximately a predetermined value.

Next, in the recording mode, the switches 2 and 3 are turned off as in the case described above, and a low level control signal is input to the terminal 50. Therefore, the transistor 46 is turned on and the transistor 45 is turned off, so that the drive current output from the current mirror circuit 51 is reduced to the semiconductor laser 1.
9, only the drive current output from the current mirror circuit 31 is supplied. As shown by the broken line in Fig. 2, this drive current is the same (
or lower) output level P1 is set to a value that can be obtained. This makes the bottom level of the output during recording the same as the output level during reproduction. In the recording mode, a recording signal is input to the terminal 22 in the same manner as described above. Therefore, a drive current at a level corresponding to the control signal input to the terminal 21 is modulated into a recording signal and supplied to the semiconductor laser 19. The control signal of the terminal 21 is such that the output of the current mirror circuit (constant current circuit) 32 is a constant current (■s
+zJ). This drive current is added to the drive current I4 from the current mirror circuit 31, so the drive current is finally calculated as follows: I, +I, +
1. ), therefore, the top level of the output of the semiconductor laser 19 is P2.

〔effect〕

As described above, the present invention provides a light source drive circuit that includes a light source that generates a predetermined light and a first light source that generates a predetermined light during recording mode and playback mode.
a first supply circuit that supplies a drive current to the light source, and a second supply circuit that superimposes a second drive current that changes in response to a recording signal in a recording mode on the first drive current and supplies it to the light source. and a third supply circuit that superimposes the third drive current on the first drive current and supplies it to the light source in the reproduction mode, and a generation circuit that generates a high frequency signal to be supplied to the light source in the reproduction mode. Therefore, the bottom level of the light source output during recording can be made equal to or lower than the level during reproduction. Also, since the bias point can be moved to an area where there is less noise due to returned light, S/
N improves.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a light source driving circuit according to the present invention, FIG. 2 is a characteristic diagram thereof, FIG. 3 is a block diagram of a conventional light source driving circuit, and FIG. 4 is a characteristic diagram thereof. 1... APC circuit 2.3... Switch 4... Operational amplifier 5, fist, capacitor 6... Hold circuits 7 to 12... Resistors 13 to 18... PNP transistor 19... Semiconductor Laser 20... Generation circuit 21, 22... Terminal 23... Operational amplifier 24... NPN transistor 25... Resistor 31, 32... Current mirror circuit 33... Differential circuit 34...・Voltage-current conversion circuits 41 to 44...Resistors 45 to 48...PNP transistors 49.50...
・Terminal 51...Current mirror circuit 52...Differential circuit or higher

Claims (1)

[Claims] a light source that generates a predetermined light; a first supply circuit that supplies a first drive current to the light source during recording mode and playback mode; and a second supply circuit that changes in response to a recording signal during recording mode.
a second supply circuit that superimposes a drive current on the first drive current and supplies the same to the light source; and a third supply circuit that superimposes a third drive current on the first drive current and supplies it to the light source in a playback mode. A light source drive circuit comprising: a third supply circuit; and a generation circuit that generates a high frequency signal to be supplied to the light source in a reproduction mode.