JPH114032A - Laser power control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser power control circuit capable of easily setting a reference level from the outside. SOLUTION: In this laser power control circuit 14 for controlling laser power which is based on a signal level read by an optical system 12 provided with a laser diode 11, a control input terminal 20 for fetching control information supplied from the outside is provided, and the reference level Vref is adjusted based on the control information inputted from an external adjustment circuit 22 via the control input terminal 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser power control (LPC) for controlling the output of a laser diode.
More particularly, the present invention relates to a laser power control circuit that controls an output of a laser diode used as a light source in an optical disk device or the like based on a signal level read by an optical system including the laser diode.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example of a system using such a laser power control circuit. In FIG. 1, an optical system 102 including a laser diode 101 is for reading recorded information on an optical disk (not shown). The RF signal read by the optical system 102 is supplied to a laser power control circuit 104 via an RF circuit 103, and is also supplied to a signal processing system (not shown) for performing signal processing such as demodulation.

[0003] The laser power control circuit 104 comprises:
A peak hold circuit 105 for holding the peak value of the RF signal; a reference level setting circuit 106 for setting a predetermined reference level Vref; an output signal of the peak hold circuit 105 and the reference level Vref set by the reference level setting circuit 106 And a comparator 107 for comparing the difference
And is integrated into an IC.

This laser power control circuit 104
, The reference level setting circuit 106 includes a current source 108 and a resistor 109 connected in series between a power supply Vcc and a power supply Vee (Vee = Vcc / 2).
The potential at the connection point A between the current source 108 and the resistor 109 is set to the reference level Vref. This reference level Vref is R
This is a reference for setting the F signal level, and is fixedly set in accordance with the RF signal level considered to be optimal for the power supply voltage to be used.

The difference between the output signal of the peak hold circuit 105 obtained by the comparator 107 and the reference level Vref is
It is supplied to an APC (Automatic Power Control) circuit 110. The APC circuit 110 controls the optical system 102 based on the difference information given from the comparator 107.
Of the laser diode 101, that is, the laser power. As a result, the RF signal level set by the reference level Vref is suppressed.

[0006]

However, in the conventional laser power control circuit 104 having the above configuration,
Since the reference level Vref is fixed in accordance with the RF signal level considered to be optimal for the used power supply voltage, the R considered to be optimal when the used power supply voltage is set low.
The RF signal level is suppressed to a level higher than the F signal level, and the optimum level shifts.

As a result, the output dynamic range of the RF circuit 103 is narrowed, and the stable region of the RF signal level with respect to the reflectivity and modulation of the disk is narrowed. This has an adverse effect on the detection of scratches on the disk and the detection of the mirror (mirror surface), and causes a reduction in the reproduction capability of the optical disk device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a laser power control circuit capable of easily setting a reference level from the outside.

[0009]

SUMMARY OF THE INVENTION A laser power control circuit according to the present invention is a laser power control circuit for controlling the output of a laser diode based on a signal level read by an optical system including a laser diode. A control input terminal for receiving given control information, reference level setting means for setting a predetermined reference level and adjusting the reference level based on the control information input via the control input terminal, and reading by an optical system. And a comparison means for comparing the obtained signal level with the reference level set by the reference level setting means and providing the difference as control information of the output of the laser diode.

In the laser power control circuit having the above structure, the reference level setting means sets the reference level in advance according to the RF signal level considered to be optimal for the power supply voltage when no control information is given from the outside via the control terminal. Set a reference level according to the circuit constants set. On the other hand, when control information is given from the outside via the control terminal in accordance with the change of the used power supply voltage, the reference level is adjusted based on the control information. Then, a difference between the signal level and the reference level is obtained by a comparator, and the laser power is controlled based on the difference.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, an optical system 12 including a laser diode 11 is for reading recorded information on an optical disk (not shown). The RF signal read by the optical system 12 is supplied to a laser power control circuit 14 via an RF circuit 13, and is also supplied to a signal processing system (not shown) for performing signal processing such as demodulation.

The laser power control circuit 14 has an R
Peak hold circuit 1 for holding the peak value of F signal
5, a reference level setting circuit 16 for setting a predetermined reference level Vref, an output signal of the peak hold circuit 15, and a reference level Vre set by the reference level setting circuit 16.
and a comparator 17 for comparing the difference f with each other and calculating the difference between the two.

In the laser power control circuit 14, the reference level setting circuit 16 is composed of a current source 18 and a resistor 19 connected in series between a power supply Vcc and a power supply Vee (Vee = Vcc / 2). 1
8 and resistor 19 at reference point Vre
f. This reference level Vref is a reference for setting the RF signal level.

Here, the reference current I of the current source 18 for determining the reference level Vref and the resistance value R0 of the resistor 19 are fixedly set in accordance with the RF signal level considered to be optimal under a certain power supply voltage. I have. The connection point A is connected to the control input terminal 20. Control information for adjusting the reference level Vref is externally supplied to the control input terminal 20. When control information is given from outside, the reference level Vref changes according to the control information.

The difference between the output signal of the peak hold circuit 15 obtained by the comparator 17 and the reference level Vref is represented by AP
It is supplied to the C circuit 21. The APC circuit 21 controls the laser power based on the difference information provided from the comparator 17. As a result, the RF signal level set by the reference level Vref is suppressed.

That is, the current Δ of the difference between the output signal of the peak hold circuit 15 and the reference level Vref is calculated as APC
VREF ± Δ by the inverting amplifier based on VREF in the circuit 21
To the voltage. Then, this VREF ± Δ voltage is
By setting VREF, which is one of the reference voltages of the PC circuit 21, the output of the APC circuit 21 is changed by the difference ± Δ voltage, and the laser power is adjusted by controlling the current flowing through the laser diode 11.

As the laser power increases, the RF level increases, and as the laser power decreases, the RF level decreases. Using this, peak hold circuit 1
By making the signal level of the output signal No. 5 equal to the reference level Vref, the RF level is suppressed to the level set by the reference level Vref.

Outside the laser power control circuit 14, there is provided an external adjustment circuit 22 for providing control information for adjusting the reference level Vref to the reference level setting circuit 16 via the control input terminal 20. The external adjustment circuit 22 includes, for example, one resistor 23 connected between the control input terminal 20 and the power supply Vee. In this example, the resistor 23 is connected between the control input terminal 20 and the power supply Vee. However, depending on the power supply voltage used, as shown by a broken line in FIG. 24 will be connected.

Here, the setting of the reference level Vref by the reference level setting circuit 16 in the laser power control circuit 14 having the above configuration will be described.

First, when no adjustment is made from the outside, that is, when no control information is given from the external adjustment circuit 22, the reference level Vref is determined by the reference current I of the current source 18 and the resistance value R0 of the resistor 19, Vref = I × It is fixed at R0 + Vcc / 2.

When setting the RF signal level lower,
As the external adjustment circuit 22, the control input terminal 20 and the power supply Ve
One external resistor 23 is connected between e. At this time,
The reference level Vref is obtained by setting the resistance value of the external resistor 23 to R1.
Then, Vref = I × (R0 // R1) + Vcc / 2. Here, R0 // R1 is a parallel combined resistance value of R0 and R1.

When setting the RF signal level higher,
As shown by a broken line in FIG. 1, one external resistor 2 is connected between the control input terminal 20 and the power supply Vcc.
4 is connected. At this time, assuming that the resistance value of the external resistor 24 is R2, the reference level Vref is as follows: Vref = R ｛I + (Vcc−I · R0−Vcc / 2)
/ (R0 + R2)｝ + Vcc / 2.

As described above, one control input terminal 20 is added to the laser power control circuit 14 formed as an IC,
Since the reference level Vref can be adjusted based on control information externally applied through the control input terminal 20, the external resistor 23 or the external resistor 24 can be simply connected to the control input terminal 20. The RF signal level can be set arbitrarily according to the power supply voltage used. Note that when both the resistor 23 and the resistor 24 are connected, the above equation does not hold.

FIG. 2 is a block diagram showing another embodiment of the present invention. In the drawing, the same parts as those in FIG. 1 are denoted by the same reference numerals. In the present embodiment, the configuration of the external adjustment circuit 25 for providing control information to the control input terminal 20 is only different from that of the external adjustment circuit 22 of the previous embodiment, and the other configurations are exactly the same.

The external adjustment circuit 25 according to the present embodiment is provided with a register 27 controlled by data from a microcomputer 26, converts the data stored in the register 27 into analog data, and provides the analog data to the control input terminal 20 as control information. And a DA converter (DAC) 28. Here, the control information given to the control input terminal 20 is based on the current I flowing into the control input terminal 20.
in or the current Iout flowing out of the control input terminal 20
Becomes

For example, when the current Iin flows into the control input terminal 20, the reference level Vref is as follows: Vref = R0 (I + Iin) + Vcc / 2. When the current Iout flows out of the control input terminal 20, the reference level Vref becomes Vref = R0 (I-Iout) + Vcc / 2.

As described above, the control information given to the control input terminal 20 by the data from the microcomputer 26, that is, the current Iin flowing into the control input terminal 20 or the current Iout flowing out from the control input terminal 20 is controlled. The RF signal level can be set arbitrarily according to the power supply voltage used.

[0029]

As described above, according to the present invention,
In a laser power control circuit for controlling laser power based on a signal level read by an optical system including a laser diode, a control input terminal for taking in control information given from the outside is provided, and a control input terminal is input through the control input terminal. Since the reference level can be adjusted based on the control information, the RF signal level can be set arbitrarily according to the power supply voltage used, so that the RF signal level at different power supply voltages is stabilized.

Thus, in the optical disk device,
For example, even when the used power supply voltage is set to be low, the output dynamic range of the RF circuit does not become narrow, so that a decrease in the reproduction capability can be suppressed. In addition, there is an advantage that it is not necessary to manufacture various types of ICs in accordance with the used power supply voltage. That is, when one type of IC manufactured according to a certain used power supply voltage is used under different used power supply voltages, it can be dealt with only by connecting, for example, one resistor to the control input terminal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

11 laser diode, 12 optical system, 13 RF circuit, 14 laser power control circuit, 15 peak hold circuit, 16 reference level setting circuit, 17 comparator, 20 control input terminal, 21 APC circuit , 22,
25 ... External adjustment circuit

Claims (3)

[Claims] 1. A laser power control circuit for controlling an output of a laser diode based on a signal level read by an optical system including a laser diode, comprising: a control input terminal for receiving control information given from outside; Reference level setting means for setting a reference level of the reference level and adjusting the reference level based on control information input through the control input terminal; signal level read by the optical system and the reference level setting means A laser power control circuit comprising: a comparison unit that compares the reference level set by the control unit with the reference level and provides the difference as control information of the output of the laser diode. 2. The laser power control circuit according to claim 1, wherein said control information is a voltage provided by a resistor connected between said control input terminal and a predetermined power supply. 3. The laser power control circuit according to claim 1, wherein the control information is a current flowing into the control input terminal or a current flowing out of the control input terminal.