JPH0731823B2 - Light source drive circuit - Google Patents

Description

The present invention relates to a light source drive circuit suitable for driving a light source such as a semiconductor laser.

[Outline of the Invention] In the present invention, the superposition of the high frequency signal of the light source is canceled at the time of recording, and the level of the bias drive current is made smaller than that at the time of reproducing.

[Conventional technology]

FIG. 3 is a block diagram of a light source drive circuit for driving a light source used in a pickup of a conventional optical disk device. When reproducing the information recorded on the optical disc, the switches 2 and 3 are both turned on. The APC circuit 1 monitors the output of the semiconductor laser 19 as a light source, compares the monitor output with a predetermined reference value, and outputs the error signal thereof. This error signal is input to the hold circuit 6 having the operational amplifier 4 and the capacitor 5 via the switch 2. The output voltage of the hold circuit 6 is input to the voltage-current conversion circuit 34 including the operational amplifier 23, the NPN transistor 24 and the resistor 25, and converted into a current. The output of the voltage-current conversion circuit 34 is a resistor 7,
8. Input to a current mirror circuit 31 as a supply circuit composed of PNP transistors 13 and 14. The current mirror circuit 31 uses a transistor to drive a driving current of a level corresponding to a signal input from the voltage / current conversion circuit 34 (hold circuit 6).
Output from 14 collectors. This drive current is supplied to the semiconductor laser 19, and the semiconductor laser 19 outputs laser light of 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 so as to correspond to a predetermined reference value.

On the other hand, the high frequency signal output from the reproduction time generation circuit 20 is superimposed on the semiconductor laser 19 via the switch 3 (and a capacitor (not shown) if necessary). As a result, the recorded information can be reproduced without being affected by the noise caused by the returning light from the disc.

The input / output characteristics of the semiconductor laser 19 are shown by the solid line in FIG. Therefore, the drive current supplied from the transistor 14
Output light of P ₁ level is emitted corresponding to I ₁ .

When recording information on the optical disk, the switch 3 is turned off in order to prevent the semiconductor laser 19 from being supplied with a current higher than the rated value. Therefore, high frequency signals are not superimposed. At this time, since the switch 2 is also turned off, the level of the driving current during reproduction is stored (held) in the capacitor 5, and the transistor 14 supplies the semiconductor laser 19 with the same level of driving current I ₁ as during reproduction. To do.

A predetermined control signal for setting the level of the drive current at the time of recording is input to the terminal 21 of the current mirror circuit 32 as a supply circuit including the resistors 11 and 12 and the PNP transistors 17 and 18. Drive current I output from the current mirror circuit 32
₃ is input to the differential circuit 33 including resistors 9 and 10 and PNP transistors 15 and 16. One transistor of the differential circuit 33
Since the recording signal is supplied to the base of 16, the driving current I ₃ is output from the collector of the other transistor 15 corresponding to the recording signal. This drive current I ₃
Is supplied to. As a result, the driving current I ₁
The current I ₂ (= I ₁ + I ₃ ) obtained by adding the drive current I ₃ and the drive current I ₃ flows. When the drive current I ₂ is input as shown in FIG. 4,
The output level of the semiconductor laser 19 is P ₂ . Eventually, the output of the semiconductor laser 19 changes between the bottom level P ₁ and the top level P _{2 according} to the recording signal.

Pits are not formed (information is recorded) at the bottom level P _{1 on the} optical disc, but pits are formed (information is recorded) at a larger top level P ₂ .

[Problems to be solved by the invention]

However, the characteristics shown by the solid line in FIG. 4 are those when a high frequency signal is superimposed in order to reduce the influence of the return light, and the characteristics when the high frequency signal is not superimposed are as shown by the broken line. As a result, the bottom level when recording
Not P ₁ , but a larger P ₃ than that. Therefore, in the worst case, pits may be formed even at the bottom level P ₃ . Further, in the vicinity of the bottom level P ₃ , noise is generally apt to occur, so that there is a drawback that the S / N becomes worse.

Therefore, the present invention prevents the formation of pits due to the bottom level and improves the S / N.

[Means for solving problems]

The present invention relates to a light source driving circuit, which corresponds to a light source that generates a predetermined light, a first supply circuit that supplies a first driving current to the light source in the recording mode and the reproduction mode, and a recording signal in the recording mode. A second supply circuit that superimposes a changing second drive current on the first drive current and supplies the light source to the light source, and a third drive current that superimposes the third drive current on the first drive current and supplies the light source to the light source in the reproduction mode. And a generator circuit for generating a high-frequency signal to be supplied to the light source in the reproduction mode.

[Action]

The light source emits a predetermined light. The drive current output from the three supply circuits and the high frequency signal output from the generation circuit are supplied to the light source. In the recording mode, the second driving current modulated by the recording signal is supplied while being superimposed on the first driving current. In the reproduction mode, the first drive current and the third drive current are added and supplied, and the high frequency signal is superimposed.

〔Example〕

FIG. 1 is a block diagram of a light source drive circuit according to the present invention, and portions corresponding to those in FIG. 3 are designated by the same reference numerals. In the present invention, the output of the current mirror circuit (constant current circuit) 51 as a supply circuit composed of the resistors 43 and 44, PNP transistors 47 and 48, and the terminal 49 corresponds to the resistors 41, 42 and PNP.
It is adapted to be supplied to the semiconductor laser 19 via a differential circuit 52 including transistors 45 and 46 and a terminal 50. Other configurations are similar to those in FIG.

The switch 2 is turned on in the reproduction 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 I ₄ which is smaller than the above-mentioned case (I ₁ ).

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 I ₅ . As a result, the transistor 46 turns off, the transistor 45 turns on, and the drive current (constant current) I ₅ output from the current mirror circuit 51 is supplied to the semiconductor laser 19 via the transistor 45.

Eventually, the semiconductor laser 19 is supplied with the drive current I ₁ (= I ₄ + I ₅ ) obtained by adding the drive current I ₄ and the drive current I ₅ .

Since the switch 3 is turned on in the reproduction mode as in the case described above, a high frequency signal is transmitted (via a capacitor (not shown)).
It is superimposed on the semiconductor laser 19. As a result, the semiconductor laser 19
The characteristic of is as shown by the solid line in FIG. 2, and its output level is P ₁ .

The reference voltage of the APC circuit 1 is set to be smaller than that in the case described above in accordance with the drive current I ₄ . Although the automatic level control by the APC circuit 1 is not performed for the component of the drive current I ₅ ,
It is possible to control the output level of the semiconductor laser 19 to a substantially predetermined value.

Next, in the recording mode, as in the case described above, the switches 2 and 3 are turned off, and a low-level control signal is input to the terminal 50. Therefore, since the transistor 46 is turned on and the transistor 45 is turned off, the drive current I ₅ output from the current mirror circuit 51 is not supplied to the semiconductor laser 19 and only the drive current I ₄ output from the current mirror circuit 31 is supplied. . This drive current I ₄ is set to a value that gives the same (or lower) output level P _{1 as} when superposed (in the reproduction mode) when the high frequency signal is not superposed as shown by the broken line in FIG. Has been done. As a result, the bottom level of the output during recording becomes the same as the output level during reproduction. The recording signal is input to the terminal 22 in the recording mode as in the case described above. Therefore terminal 21
A drive current having a level corresponding to the control signal input to is modulated into a recording signal and supplied to the semiconductor laser 19. Terminal
21 control signal is current mirror circuit (constant current circuit) 32
Output is set to constant current (I ₅ + I ₃ ). Since this drive current is added to the drive current I ₄ from the current mirror circuit 31, the drive current is finally I ₂ (= I ₄ +
I ₅ + I ₃ ). Therefore, the top level of the output of the semiconductor laser 19 is P ₂ .

〔effect〕

As described above, according to the present invention, in the light source drive circuit, the first light source for generating a predetermined light and the first light source in the recording mode and the reproduction mode are provided.
Supply circuit for supplying the drive current of the above to the light source, and a second supply circuit for superimposing the second drive current that changes corresponding to the recording signal in the recording mode on the first drive current and supplying it to the light source. And a third supply circuit that superimposes the third drive current on the first drive current in the reproduction mode and supplies the light source to the light source, 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 output of the light source during recording can be made equal to or lower than the level during reproduction. In addition, since the bias point can be moved to a region where there is little noise due to the returned light, S / N
Is improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a light source drive circuit of the present invention, FIG. 2 is a characteristic diagram thereof, FIG. 3 is a block diagram of a conventional light source drive circuit, and FIG. 4 is a characteristic diagram thereof. 1 ... APC circuit 2,3 ... Switch 4 ... Operational amplifier 5 ... Capacitor 6 ... Hold circuit 7 to 12 ... Resistance 13 to 18 ... PNP transistor 19 ... Semiconductor laser 20 ... Generation circuit 21, 22 …… Terminal 23 …… Operational amplifier 24 …… NPN transistor 25 …… Resistance 31,32 …… Current mirror circuit 33 …… Differential circuit 34 …… Voltage / current conversion circuit 41 to 44 …… Resistance 45 to 48 …… PNP transistor 49,50 ...... Terminal 51 ...... Current mirror circuit 52 ...... Differential circuit

Claims (1)

[Claims] 1. A light source for generating a predetermined light, a first supply circuit for supplying a first drive current to the light source in a recording mode and a reproducing mode, and a change in response to a recording signal in the recording mode. A second supply circuit that superimposes a second drive current on the first drive current and supplies the light source to the light source; and a third drive current that superimposes a third drive current on the first drive current in the reproduction mode to the light source. A light source drive circuit comprising: a third supply circuit for supplying; and a generating circuit for generating a high frequency signal to be supplied to the light source in a reproduction mode.