JP2698380B2 - Semiconductor laser driver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device, and more particularly to a semiconductor laser driving device in which the emitted light amount of a semiconductor laser rapidly falls within a predetermined range when the emitted light amount is out of a predetermined range. The present invention relates to a semiconductor laser driving device which can be controlled to be as follows.

[Conventional technology]

Conventionally, a semiconductor laser driving device has a very poor laser temperature characteristic. Therefore, when used in an environment where the ambient temperature changes, the driving current supplied to the semiconductor laser is periodically corrected to correct the emitted light amount. And a sampling cycle setting means for controlling the operation cycle of the feedback control means.

That is, as shown in FIG.
It is excited by a drive current E output from the V / I converter 1 and emits light with an emission light amount P corresponding to the magnitude of the drive current E. Is detected by the photo sensor 3,
The voltage signal Sa is converted into a voltage signal Sa corresponding to the light amount via the I / V converter 4, and the voltage signal Sa is converted into a digital signal Sb by the A / D converter 5 and input to the CPU 6.
The CPU 6 determines whether to increase or decrease the current control output signal Sc by referring to data corresponding to the digital signal Sb corresponding to the emission light amount P of the semiconductor laser 2 stored in advance as a table based on And outputs it to the latch circuit 7, and further passes through the D / A converter 8 to the voltage signal S.
After being converted to d, it is input to the V / I converter 1, and a drive current E corresponding to this voltage signal Sd is supplied from the V / I converter 1 to the semiconductor laser 2. The sampling cycle setting means is built in the CPU 6, and operates the feedback control means at regular intervals.

Here, as shown in FIG. 4, the initial value of the emission light amount P of the semiconductor laser 2 when the semiconductor laser 2 is turned on is P _0, the target amount of light emitted semiconductor laser 2 which is a target value P ₁
Therefore, the operation of the feedback control means will be described in more detail.

The digital signal Sb input corresponding to the initial emission light value P ₀ is taken into the CPU 6 from the A / D converter 5, and data corresponding to the target emission light intensity P ₁ from a table previously input in the CPU 6. And outputs an output signal Sc obtained by increasing the drive current E by ΔI. The series of operations of data input from the A / D converter 5 to the CPU 6, data comparison, and data update of the D / A converter 8 are repeated at a fixed sampling period Δt, and the emission of the semiconductor laser 2 is eventually completed. Light intensity P
There reaches a target light emission amount P _1, becomes stable in a variation range of the emitted light amount corresponding to [Delta] I. The above-mentioned ΔI is a current amount corresponding to a variation range ΔP or less of the emission light amount P which is allowed in a system such as an optical disk device or a laser printer.

[Problems to be solved by the invention]

However, in the conventional semiconductor laser driving device,
For the the sampling period Δt to be set by the sampling period setting means is constant, for example when the emission light intensity P such when the semiconductor laser is turned on deviates significantly from the target light emission amount P ₁ is the emission light intensity P It arises a problem that the time to correct the target amount of light emitted P ₁ becomes considerably long. In order to solve such a problem, the sampling period Δt may be set to be short.
Since the time spent for feedback control cannot be increased beyond a certain value in the operation time, there is naturally a limit in setting the sampling period Δt to be short.

[Means for solving the problem]

The present invention has been made in order to solve the above-mentioned problem, and is capable of rapidly controlling the emission light amount of a semiconductor laser to fall within a predetermined range when the emission light amount of the semiconductor laser is out of a predetermined range. It was made.

That is, the semiconductor laser driving device according to the present invention includes a current generating unit that supplies a driving current to the semiconductor laser, and an output light amount of the semiconductor laser, and the current generation unit detects the emitted light amount so as to be within a predetermined range. In a semiconductor laser driving apparatus comprising: a feedback control means for setting a drive current value; and a sampling cycle setting means for controlling an operation cycle of the feedback control means, an output light amount of the semiconductor laser detected by the feedback control means is the predetermined amount. Comparing means for determining whether or not the output is within the range, wherein the sampling cycle setting means responds to the output of the comparing means, and when the emitted light amount of the semiconductor laser is within a predetermined range, the feedback control means The operation cycle is set to be long, and when the operation cycle is out of the predetermined range, the operation cycle is set to be short. It is characterized in.

(Operation)

With the above configuration, when starting the semiconductor laser or the like, the sampling cycle is shortened when the emitted light amount largely deviates from the predetermined range of the target emitted light amount. On the other hand, when the emitted light amount is within a predetermined range of the target emitted light amount or slightly deviates from the predetermined range of the target emitted light amount, the sampling cycle is extended, and during the CPU operation time. It is possible to reduce the time spent for controlling the amount of light emitted from the CPU and reduce the load on the CPU.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 3, the semiconductor laser driving apparatus detects a V / I converter 1 serving as a current generating means for supplying a driving current E to the semiconductor laser 2 and a light emission amount P of the semiconductor laser 2 and outputs the light. V / I so that the light amount P is within a predetermined range.
The apparatus includes feedback control means for setting a drive current value of the converter 1 and sampling cycle setting means for controlling an operation cycle of the feedback control means.

The feedback control means includes a photosensor 3 composed of a photodiode that outputs a current corresponding to the amount of light P emitted from the semiconductor laser 2, an I / V converter 4 that converts the output of the photosensor 3 into a voltage signal Sa, An A / D converter 5 for converting the output of the / V converter 4 into a digital signal Sb, a CPU 6,
A latch circuit 7 that latches the output signal Sc of the PU 6 and a D / A converter 8 that converts the latch signal Sc ′ latched by the latch circuit 7 into a voltage signal Sd and outputs the voltage signal Sd to the V / I converter 1 It is configured. Data corresponding to the digital signal Sb corresponding to the amount of emitted light P of the semiconductor laser 2 is input to the CPU 6 as a table.

The sampling period setting means is constituted by a timer (not shown) built in the CPU 6, and this timer is
A short-period sampling period B in which the operation of U6 is monopolized by controlling the output light amount, and a sampling period A set longer than the sampling period B within a range required for controlling the output light amount in a stable state. And two types of periods can be set.

Further, the CPU 6 incorporates a control program as shown in FIG. That is, when the semiconductor laser driving device is started and the control program is started, first, data “UP” is input to the first variable 1 as an initial setting (S
1) After that, the digital signal Sb is taken in from the A / D converter 5 (S2).

Then, the digital signal Sb and the target emission light amount of the table
By comparing the data corresponding to P _1, these magnitude relationship is determined (S3), if the digital signal Sb is smaller than the data corresponding to the target light emission amount P ₁ of the table (for A / D <Table ), Data for increasing the drive current E by ΔI is output as the output signal Sc (S4), and the second variable L is set to “Up” (S5).

On the other hand, the digital signal Sb and the target emission light amount P _{1 of the} table
(S3) to compare the digital signal
In the case Sb is greater than the data corresponding to the target light emission amount P ₁ of the table (for A / D> tables), the drive current E
Is output as the output signal Sc (S6), and the second variable L is set to "Down" (S7).

As described above, after inputting the second variable L, it is determined whether or not the second variable L is equal to the first variable l, so that the state at the previous sampling and the state at the current sampling are determined. Are determined to be the same (S8). When L = 1, the sampling period B set by the timer elapses (S9), and when L ≠ 1, after the sampling period A set by the timer elapses (S10). Further, after substituting the second variable L for the first variable l (S11), the digital signal Sb is output from the A / D converter 5.
It returns to the step (S2) of inputting.

On the other hand, the digital signal Sb and the target emission light amount P _{1 of the} table
As a result of comparison with the data corresponding to (S3), if both are passed (A / D = table), after the sampling period A set by the timer elapses without changing the drive current E, (S10) Further, the second variable is set to the first variable l.
After the variable L is substituted (S11), the process returns to the step (S2) of inputting the digital signal Sb from the A / D converter 5.

According to the semiconductor laser driving device configured as described above, for example, as shown in FIG. 2, the semiconductor laser driving device is turned on, and the initial value of the emitted light amount P of the semiconductor laser 2 is P ₀ , if the target amount of light emitted semiconductor laser 2 to be P _1, as shown in FIG. 1, the digital signal Sb corresponding to the initial value P ₀ from the a / D converter 5 is inputted to the CPU 6 (S2), Digital signal Sb and target emission light amount P _{1 of} table
As a result of comparison with the data corresponding to
There is judged to be smaller than the data corresponding to the target light emission amount P ₁ of the table (S3), and the data to the drive current E increases ΔI is output as an output signal Sc (S4), thereby V / I conversion The output of the device 1 is increased by ΔI, and the emitted light amount P of the semiconductor laser 2 is increased.

Thereafter, the fact that the drive current E has been increased by ΔI is stored in the CPU 6 by setting the second variable L to “Up” (S
Five). Further, after that, it is checked whether or not the drive current E has been continuously increased by comparing what was input to this variable L in the initial state or at the time of the previous sampling with the first variable l ( S8). During the continuous increase, the next sampling is performed after the elapse of the sampling period B of the speed used exclusively for controlling the output light amount of the operation of the CPU 6 (S2). Then, a series of operations such as data input from the A / D converter 5 to the CPU 6, data comparison, and data update of the D / A converter 8 are repeated at a predetermined sampling period B, whereby the semiconductor laser 2 emission light intensity P is to reach a target light emission amount P ₁ in a short time in the [Delta] T.

Light emission amount P of the semiconductor laser 2 has reached the target light emission amount P _1, when the data corresponding to the target light emission amount P ₁ of the digital signal Sb and the table equal, sampling the timer without changing the drive current E is set after a lapse of period a (S10), further, since by substituting the second variable L to the first variable l (S11), and inputs the digital signal Sb from the a / D converter 5 at time T ₁ Return to step (S2).

In this point T _1, the digital signal Sb is larger than the data corresponding to the target light emission amount P ₁ of the table, D /
The data output to the A converter 8 is data for reducing the drive current E by ΔI (S6). Therefore, the second variable L is set to "Down", it is determined that the state is different from the state at the time of the previous sampling (S8), and after the lapse of the sampling period A (S10), the second constant L is set to the first constant l. "Down" which is a variable L
After substituting (S11), at time T ₂ so that the next sampling is performed. At this point, since the emission light intensity P is smaller than the target light emission amount P _1, D / A converter 8
Is the data for increasing the drive current E by ΔI (S4). At this time, the second variable is “U
p "(S5), and is determined to be different from the state at the time of the previous sampling (S8).
(S10), the second variable L "Dewn" is substituted for the first variable l (S11), and then the next sampling is performed.

Thereafter, by the control for reducing control and ΔI to ΔI increases the drive current E for each sampling cycle A are repeated alternately, stable to light emission amount P of the semiconductor laser 2 is increased or decreased within a predetermined range of the target amount of light emitted P ₁ State will be maintained.

In the case of change of the drive current E from the target light emission amount P ₁ as it is necessary to vary greater than ΔI to the target light emission amount P ₂ also, similarly, from the time of changing the sampling period of the short period it can reach the light emission amount P in a short time by a sampling period B to the new target light emission amount P _2.

〔The invention's effect〕

As described above, the semiconductor laser driving device according to the present invention includes a current generating unit that supplies a driving current to the semiconductor laser, and an output light amount of the semiconductor laser. In a semiconductor laser drive device comprising a feedback control means for setting a drive current value of the means and a sampling cycle setting means for controlling an operation cycle of the feedback control means, the emitted light amount of the semiconductor laser detected by the feedback control means Has a comparing means for determining whether or not is within the predetermined range, wherein the sampling cycle setting means responds to the output of the comparing means, and when the output light amount of the semiconductor laser is within the predetermined range, the feedback The operation cycle of the control means is set to be long, and when it is out of the predetermined range, the operation cycle is set to be short. Than it is.

Accordingly, when the emission light amount of the semiconductor laser greatly deviates from the range of the target emission light amount, the sampling cycle, which is the operation cycle of the feedback control means, is shortened as much as possible until the emission light amount reaches the target emission light amount. In addition, when the deviation of the emitted light amount from the range of the target emitted light amount is small, there is an effect that the sampling cycle is lengthened and the load on the CPU can be reduced.

[Brief description of the drawings]

1 to 3 show one embodiment of the present invention. FIG. 1 is a flowchart showing the flow of a control program incorporated in a CPU in a semiconductor laser driving device, and FIG. Showing the relationship between the intensity and the amount of emitted light
FIG. 3 is a block diagram schematically showing a semiconductor laser driving device, showing a −P characteristic and an emission light amount control characteristic. FIG. 4 is a view showing a conventional semiconductor laser driving device.
FIG. 4 is a characteristic diagram illustrating a −P characteristic and an emission light amount control characteristic. 1 is a V / I converter as current generating means, 2 is a semiconductor laser, 3 is a photo sensor, 4 is an I / V converter, 5 is an A / D converter, 6 is a CPU, 7 is a latch circuit, 8 is It is a D / A converter.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-314569 (JP, A) JP-A-62-286292 (JP, A) JP-A-61-217080 (JP, A)

Claims (1)

(57) [Claims] 1. A current generating means for supplying a driving current to a semiconductor laser, and a feedback detecting a light emitting amount of the semiconductor laser and setting a driving current value of the current generating means so that the light emitting amount is within a predetermined range. A semiconductor laser driving device comprising a control unit and a sampling cycle setting unit for controlling an operation cycle of the feedback control unit, wherein the emitted light amount of the semiconductor laser detected by the feedback control unit is within the predetermined range. Wherein the sampling cycle setting means responds to the output of the comparing means, and sets the operation cycle of the feedback control means to be long when the emitted light amount of the semiconductor laser is within a predetermined range; The semiconductor laser drive is characterized in that the operating cycle is set to be short when it is out of the predetermined range. Apparatus.