JPS63140432A - Laser driving circuit - Google Patents

Abstract

PURPOSE:To write data to a recording medium regardless of the change in the lapse of time of the slope efficiency of a laser light source by detecting the level of a laser light corresponding to the prescribed pattern of writing data and controlling to output the light of the prescribed writing level with a laser light source. CONSTITUTION:Writing data WD have a prescribed training pattern and a writing data pattern and a light output PL of a laser diode 23 comes to be the emitting light of a prescribed level in accordance with the training pattern. The voltage for compensation from a differential circuit 35 is a light output level of the part reduced by the deterioration in the lapse of time to a slope efficiency eta of the laser diode 23, the reduced output is compensated by a current iC2 of a current source 26 for compensation and a power sufficient to the writing can be obtained. Thus, in order to control the output level of a laser light source at the time of writing the data by a prescribed pattern, the data can be written to the recording medium regardless of the change with passage of time of the slope efficiency of the laser light source.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a radar drive circuit used for writing data on a recording medium with a laser and for use in a neck wear or the like for reading written data.

BACKGROUND OF THE INVENTION Conventionally, this type of laser drive circuit, as shown in FIG.
A terminal 1 to which write data (WD) is input is connected to drive a write switch 2, and both ends of the write switch 2 are connected to one end of a constant current source 3 for writing and one end of a current source 4 for reading (- The other end of the writing constant current source 3 and the other end of the reading current source 4 are connected to a negative potential voltage source (-■).

One end of the write switch 2, to which one end of the read current source 4 is connected, is connected to the cathode of a laser diode 5 that outputs laser light for writing data to a storage medium and reading written data. The anode of the laser diode 5 is grounded.

Further, the cathode of the pin photodiode 6 that receives the output light of the laser diode 5 is grounded, and the anode is connected to one of the input terminals of the adder 8. This adder 8
The other input terminal is grounded via a controlled current source 7, and the output terminal is connected to an input terminal of a current/voltage (I/V) conversion circuit 9.

The output terminal of the I/V conversion circuit 9 is a sample hold (S/H) for controlling the drive current of the reading current source 4.
connected to the data input terminal of the circuit 10, and the S/H circuit 10
The control signal input terminal of the read/write control signal (R
, /W ) is connected to the input terminal 11 , and the control signal output terminal is connected to the reading constant current source 4 .

In the above configuration, when reading data (-, the write switch f-2 is always off, and the S/H circuit 10 is in the through state by the low level read control signal R as shown in FIG. 5 (1). It is.

In this case, the current of the laser diode 5 and the conversion efficiency (slope efficiency) are iLD, η, and the reading current source 4, respectively.
Assuming that the current is 'Rit,p), the output light PL of the laser diode 5 is PL:ηit, as shown in FIG.

It is. However, PL is an increment of the threshold current 'lh required for the laser diode 5 to output laser light.

Therefore, the reading current source 4, the laser diode 5
, bin photodiode 6, control current source 7, adder 8
, a closed loop composed of an I/V conversion circuit 9 and an S/H circuit 10, which converts the current of the reading current source 4 to 1n.
, D), the output light PL of the laser diode 5 necessary for reading can be obtained.

On the other hand, in the case of writing, the S/H circuit 1o operates as shown in FIG.
The write switch 2 controls the read current source 4 by holding the output voltage of the I/V conversion circuit 9 during reading by using the high-level write control signal W as shown in 1). It is turned on/off by write data (WD) as shown in FIG. 5(2).

In this case, the current iLD of the laser diode 5 when the write switch 2 is turned on is the current iR of the reading current source 4 and the current iw of the constant current source 3 for writing, as shown in FIG. 5(3). is the added value.

Therefore, the output light PL of the laser diode 5 is
As shown in Figures (4) and 6, pt, = η(iR+I
w) By selecting the constant current source 3 for writing, the output light PL of the laser diode 5 necessary for writing can be obtained.

Problems to be Solved by the Invention However, in the above-mentioned conventional laser drive device,
As shown by the broken line in FIG. 6, when the slope efficiency η of the laser diode 5 decreases due to changes over time, the output light PL of the laser diode 5 necessary for writing cannot be obtained, and therefore data cannot be written to the storage medium. There is a problem that it cannot be written to.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a laser drive circuit that can write data to a storage medium regardless of changes in slope efficiency of a laser light source over time.

Means for Solving the Problems In order to solve the above problems, the present invention detects the level of laser light when a laser light source outputs laser light corresponding to a predetermined pattern of written data, and The present invention is characterized in that the laser light source is controlled to output light at a predetermined writing level when writing data, depending on the level set.

According to the above configuration, the present invention writes data to a storage medium regardless of changes in the slope efficiency of the laser light source over time in order to control the output level of the laser light source during data writing using a predetermined pattern of the write data. be able to.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to the drawings. 1 is a block diagram showing an embodiment of the laser drive circuit according to the present invention, FIG. 2 is a timing chart of the main signals of the circuit of FIG. 1, and FIG. 3 is a diagram of the laser diode of FIG. 1. FIG. 3 is a diagram showing drive current vs. light output characteristics.

In Figure 1, 21 is a terminal to which write data (WD) is input, 22 is turned on or off depending on the data when write data is input to the input terminal 21; C is always turned off when no write data is input. This is the write switch 2.
A cathode of a laser diode 23 and one end of a reading current source 24 are connected to one end of the reading current source 24 .

The anode of the laser diode 23 is grounded, and the other end of the reading current source 24 is connected to a negative potential voltage source (-■).

Write suin? The other end of 22 is connected to one end of a writing constant current source 25 and one end of a compensation current source 26 for compensating the output light of the laser diode 23 during writing, and is connected to the other end of the writing current source 25 for compensation. current source 26
The other end is connected to a negative potential voltage source (-■).

Further, 27 is a bin photodiode that receives light from the laser diode 27, and the bin photodiode 27
The cathode of is grounded, and the anode is connected to one of the input terminals of adder 28.

29 is a control current source that controls the current flowing through the laser diode 23 (-); the input terminal of the control current source 28 is grounded, and the output terminal is connected to the other input terminal of the adder 28;

30 converts the current from the adder 28 into a voltage C 71
An RN pressure (I/V) conversion circuit, 31c, a sample hold (S/H) circuit that controls the read current source 24 by the output voltage of the I/V conversion circuit 30, and 32, a read/write control signal (R/W); ) is the input terminal.

Further, 33 is an integration circuit that integrates the output voltage of the voltage/volt conversion circuit 30, 34 is a write reference signal input terminal, and 35
is a differential circuit that calculates a compensation voltage by subtracting the output voltage of the integrating circuit 33 from the voltage of the write reference signal from the input terminal 34; 36 is a memory control signal input terminal;
37, the differential circuit 3 is controlled by the control signal from the input terminal 36.
This memory stores the voltage data from 5 and outputs it to the compensation current source 26.

Next, the operation of the embodiment according to the above configuration will be explained.

In FIG. 1, in the above configuration, first in the case of reading, the writing switch f22 is always open;
/H circuit 31 receives read signal R(
As shown in FIG. 2 (1)), it is in the through state.

Here, if the current of the bin photodiode 27 is iD, the current of the control current source 29 is icx, and the current-voltage conversion coefficient of the I/V converter 30 is "1", then the reading current source 241
The control voltage VC of is Ver= iD+ ict.

Further, if the conversion coefficient of the reading current source 24 is α, then
The current iR of the reading current source 4 is iR=αVCI, and when the conversion efficiency (slope efficiency) of the laser diode 23 is η, the optical output P of the laser diode 23 is
L is PL:ηit.

It is. However, as shown in Figure 3, iLD is
th increment.

Also, if the sensitivity of the bin photodiode 27 is β, then
The current ID of the bin photodiode 27 can be expressed as ID=βPL.

Therefore, iLD is: it, n = iR = αvc1 = α(io+1c1) = α(βPL + IcI > = α(βηiLo+1cx), i.e. it, o = αicx/(1-αβη). Therefore, the laser diode 23 optical output P
L is PL:ηit.

=αη! c1/(1-αβη) ・・・・・・(1
), and according to equation (1), the optical output PL of the laser diode 23 emitted to read data written on the storage medium is determined by the current i of the control current source 29.
It can be controlled by setting cx.

Furthermore, since 1<<αβη, the optical output PL is usually: Pt,=! at/β ・・・・・・・・・(
2), therefore, by equation (2),
The optical output PL is determined by the sensitivity β of the bin photodiode 27 and the current iC1 of the control current source 29.

As shown in FIG. 3, this optical output PL is determined when the slope efficiency η of the laser diode 23 deteriorates (indicated by the broken line in the figure).
Even the power is enough for reading.

On the other hand, in the case of writing, as shown in FIG. 2 (1), the 8/H circuit 10 is put into a hold state by the write control signal W from the input terminal 32, and the output voltage of the I/V conversion circuit during reading is changed. At the same time, the write data (WD) from the input terminal 21 is held as shown in FIG. 2 (2).
The write switch 22 is turned on/off by.

This write data (WD) generally has a predetermined training pattern for PLL pull-in and a write data pattern, so the optical output PL of the laser diode 23 is as shown in FIG. 2 (3) and (4). Then, the emitted light is at a predetermined level according to the training pattern.

The optical output PL according to this training pattern (2) is received by the bin photodiode 27 and photoelectrically converted, the adder 28 adds the current icl of the control current source 29, and the I/V conversion circuit 30 as shown in FIG. 5) is converted into the voltage ■c as shown in FIG.

The integrating circuit 33 integrates this input voltage vc and calculates the result as shown in FIG.
An integral signal v■ as shown in 6) is output to the differential circuit 35. That is, this integral signal vI corresponds to the average value (2) of the optical output PL of the laser diode 23.

The differential circuit 35 calculates a compensation voltage by subtracting the output voltage vl of the integrating circuit 33 from the voltage of the write reference signal from the input terminal 34, and this compensation voltage data is used as the second
The data is stored in the memory 37 by the sampling pulse MS input to the memory control signal input terminal 36 as shown in FIG. For control voltage V
C2 is output.

That is, in the above embodiment, the compensation voltage from the differential circuit 35 is the optical output level corresponding to the decrease in the slope efficiency η of the laser diode 23 due to aging deterioration. Therefore, as shown by the broken line in FIG. The decreased optical output is compensated by the current ic2 of the compensation current source 26, and sufficient power for writing can be obtained.

In the above embodiment, the output light of the laser diode 23 is controlled by the writing constant current source 25 and the compensation current source 26, but the output light of the laser diode 23 is controlled by one writing current source. It may be configured to do so.

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention provides a predetermined pattern of write data (2) to control the output level of the laser light source during data writing, regardless of changes over time in the slope efficiency of the laser light source, etc. Data can be written to a storage medium.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the laser drive circuit according to the present invention, FIG. 2 is a timing chart of the main signals of the circuit of FIG. 1, and FIG. 3 is a diagram of the laser diode of FIG. 1. Driving current vs. optical output characteristic diagram, Figure 4 is a block diagram showing a conventional example, Figure 5 is a timing chart of the main signals of the circuit in Figure 4, Figure 6 is the drive of the laser diode in Figure 4. FIG. 3 is a current vs. light output characteristic diagram. 21...Write data (W/D) input terminal, 2
2... Write switch, 23... Laser diode, 24... Current source for reading, 25... Constant current source for writing, 26... Current source for compensation, 27... Pin photodiode, 28... Adder, 29... Control current source, 30... Current voltage (I/V) conversion circuit, 31
...Sample hold (S/H) circuit, 32...Read/write control signal (几/W) input terminal, 33...
・Integrator circuit, 34...Writing reference signal input terminal, 3
5...Differential circuit, 36...Memory control signal input terminal, 37...Memory, WD...Write data. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) A light source that outputs a laser beam to write data to a storage medium and read the written data; a first current source that drives the light source when writing and reading data; and a first current source that drives the light source when writing data. second to drive
a current source, and the first current source is controlled so that the light source outputs light at a predetermined reading level when reading data, and the light source is driven by the drive current when reading the data when writing data. So the first
a first current source control means for controlling a current source; detecting a level of the laser beam when the light source outputs a laser beam corresponding to a predetermined pattern of write data; and based on the detected level, The second light source outputs light at a predetermined writing level when writing data.
and second current source control means for controlling the current source.