JPS61180944A - Controller for recording light quantity of optical disk device - Google Patents

Abstract

PURPOSE:To ensure the recording with uniform quality by providing an averaging means for output of a monitor sensor and a detection means which detects the difference between the output level of the averaging means and a prescribed level and controlling the drive current of a light source in response to the output of said detection means. CONSTITUTION:The output of a monitor sensor 4 set into a position close to a laser diode 1 is averaged by an averaging means consisting of an LPF 5 and an operational amplifier 6. It is decided by a comparator 9 whether the averaged output (c) is less than the target values (Vh, Vl) or not. If the output (c) exceeds the target values, a counter 11 performs subtraction. While the counter 11 performs addition when the output (c) is less than the target values. For the counting timing, a timer 12 sends the timing signal to a counting gate 10 based on a signal (a) so that the counting action is started at a time point when the output (c) is stabilized after a writing action is started. The count value is converted into analog signals by a D/A converter 13 for control of a recording current source 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a recording light amount control device for an optical disc device.

BACKGROUND OF THE INVENTION Conventionally, laser diodes, which are commonly used as light sources in optical disk devices, have light intensity versus current characteristics that change depending on the temperature during operation, and therefore the light intensity must be stabilized using an automatic light intensity control device. FIG. 2 shows the temperature change of the general light amount vs. current characteristic of a laser diode. As can be seen from Figure 2, when the temperature changes, the threshold current value Ith for starting laser oscillation and the slope of the straight line of the light quantity vs. current characteristic after starting laser oscillation change, but the change in threshold current Ith changes. Therefore, in conventional devices, the drive current of the laser diode is controlled in a closed loop so that the low light amount Pr used for reading is constant, and the high light amount Pw used for recording is determined by the difference between Pw and Pr. It was obtained by open loop control in which a constant current corresponding to the difference was added to the drive current to obtain Pr. This is because it is not easy to stably and accurately detect the peak value of the recording pulse light, so it is difficult to control in a closed loop, and the change in the slope of the laser diode's light amount vs. current line is small.

The above-mentioned conventional light amount control device cannot be used when the light amount vs. current characteristics of the laser diode changes over time, when there is a large change in the environmental temperature, or when the recording medium is sensitive to changes in the recording light amount. However, there was a drawback that the recorded signal quality may not be uniform if the recording light amount changes.

Purpose of the Invention The present invention has been made to eliminate the above-mentioned drawbacks of the conventional methods, and provides a recording light amount control for an optical disk device that enables recording of uniform quality regardless of changes in light source characteristics over time, temperature changes, etc. The purpose is to provide equipment.

Composition of the Invention The recording light distribution device according to the present invention includes a monitor sensor that monitors the output light amount of a recording light source, an averaging unit that averages the output of the monitor sensor, and an averaging unit that averages the output of the monitor sensor at predetermined timings. The light source is characterized in that it comprises a detection means for detecting a level difference between the output level of the means and a predetermined reference level, and the driving current of the light source is controlled in accordance with the output of the detection means.

Next, the present invention will be explained with reference to the drawings.

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

In the figure, a laser diode 1 is connected to a read current source 2 and also to a write current source 3 via a write switch 14 . A one-pass filter 5 for the output of the monitor sensor 4 built in the vicinity of the laser diode 1
and an operational amplifier 6, and then supplied to comparators 7 and 9. In the comparator 7, the averaged output is compared with the target value e, and the comparison output controls the read current source 2 through the sample and holder 8 which holds the value immediately before writing during writing.

The comparator 9 consists of operational amplifiers OPI and OP2 whose reference inputs are the reference voltages Vh and Vt (Vh) Vt provided by the voltage dividing resistors R1 to R3, respectively.
When the above averaged output is higher than the reference voltage vh, oPl
outputs a high level when it is smaller than the reference voltage Vt.
20 is adapted to generate a high level output.

These outputs are an AND game in count gate 10)
This serves as an input for each of 10a and 10b. AND gate 1
A timing signal generated by the timer 12 based on the signal a is supplied as the other input of 0a and 10b.

The output of the AND gate 10a controls the amplifier count of the counter 11, and the output of the AND gate 10b controls the counter 11.
Control the down count. The counter 11 counts up or down the clock output from the clock generator 15. The output of the counter 11 is sent to the D/A converter 13.
It is converted into a voltage proportional to the count value and controls the recording current source 3.

Next, the operation of the device of the present invention will be explained.

Figure 3 shows the structure of the data to be recorded. The first several tens of pits P are a fixed pattern for phase locking that is generally used when reading. In a system based on a data string that does not have this pattern, it is basically used by changing it so that this pattern is added.

FIG. 3C shows the output of the operational amplifier 6 obtained when recording the above data string. Since the first few tens of bits have a constant pattern, the average value is also constant, and therefore the amount of light and the output C of the operational amplifier 6 exhibit a linear proportional relationship. Furthermore, since the operational amplifier 6 is used as the circuit element of the averaging circuit, an extremely stable output C can be obtained against changes in power supply voltage and temperature.

A comparator 9 determines whether the output C is within the target values (Vh, Vt), and if it is high, the counter 11 is operated to subtract, and if it is low, it is incremented. The timer 12 sends a timing signal as shown in FIG. 3d to the current controller 10 based on the signal a so that the counting is performed when the writing starts and the output C becomes stable. The count value is converted into an analog signal by a converter 13, and the recording current source 3 is controlled so that a small current flows when the count value becomes small, and a large current flows when the count value becomes large.

By doing so, the amount of recording light is controlled so as to fall within the target value set in the comparator 9, so that it is possible to record with uniform quality.

As described in detail, the present invention accurately and stably controls the light intensity of the laser diode during writing, thereby making it possible to record uniform quality regardless of changes in the characteristics of the laser diode over time or changes in temperature. It has the effect of making it possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the light amount versus current characteristics of a laser diode used in the present invention, and FIG. 3 is a waveform diagram of each part of FIG. 1. Explanation of symbols of main parts 1...Laser diode 2...Reading current source 3...Recording current source 4.
...Monitor sensor 9...Comparator 11...Counter 13...Converter to boar 14...Write switch

Claims (1)

[Claims] A monitor sensor that monitors the output light amount of a recording light source, an averaging device that averages the output of the monitor sensor, and a detection device that detects a level difference between the output level of the averaging device and a predetermined reference level at each predetermined timing. and
A recording light amount control device for an optical disc device, characterized in that a driving current of the light source is controlled in accordance with an output of the detection means.