JPS62298032A - Light intensity control circuit - Google Patents

Abstract

PURPOSE:To stably control the light intensity by executing the control at the time of recording, based on the light intensity of a front emitted light of a light source. CONSTITUTION:In case of a recording mode, a sample holding circuit 9 becomes a sample mode at the time of reproduction, therefore, by a reproducing current correcting loop by a rear monitor, the light intensity of a laser diode 1 is controlled so as to become constant, based on a detected current of a photodiode 2. At the time of recording, a sample holding circuit 19 becomes a sample mode, therefore, by a recording current correcting loop by a front monitor, a peak value of the light intensity of the laser diode 1 is controlled so as to become constant, based on a peak value which has been detected by a peak detecting circuit 14. Accordingly, even a pickup having a scoop can control stably the light intensity.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention The present invention relates to a light intensity control circuit for a light source in a J5 optical information recording/reproducing apparatus.

Seiken Technology As an example of this type of circuit, the circuit shown in FIG. 4 is known. This light intensity control circuit has a circuit configuration of a peak power control rack, and the light intensity (power) of the rear emitted light from the laser diode 1, which is the light source, is controlled by the monitor photodiode built into the case of the laser diode 1. Detected by (photodetector) 2. The detection current of the photodiode 2 is converted into a voltage by an I (current)-V (voltage) conversion circuit 3 and supplied to a peak detection circuit 4.

The peak detection circuit 4 detects the first peak of the output voltage of the mV conversion circuit 3 and detects the comparison power of the comparison circuit 5. Comparison circuit 5
The normal voltage Vrcf from the normal voltage source 6 is supplied as a 1 tB input.

The error voltage, which is the comparison output of the comparison circuit 5, is converted into a current by the Vl conversion circuit 7, and becomes a recording current flowing through the laser diode 1 when recording information. That is, the laser diode 1 outputs data logic "1" and "○" based on the recorded information.
The laser diode 1 is switched by a switching circuit 8 consisting of transistors Q+ and Qz, which turn on and off depending on the voltage, and at this time, the output current of the V-I conversion circuit 7 flows through the laser diode 1 as a recording current.

Due to the above closed loop, the peak value of the light intensity of the laser diode 1 during recording is li%I\-voltage Vref
The recording current is controlled so that it reaches a predetermined value determined by .

In a light intensity control circuit with such a configuration, the bone nerve function at the peak value of the light intensity starts for the first time after data recording starts, but since the servo loop has a finite band, the laser Since it takes a long time for the light intensity of diode 1 to rise to a predetermined value as shown in FIG.
It has been found that a section for increasing the light intensity is required between the (1 dentifier) portion and the recording area, and for this reason, it is not possible to increase the recording density of the disk.

FIG. 6 shows another conventional example of a light intensity control circuit having a sample-and-hold circuit configuration, in which functional blocks equivalent to those in FIG. 4 are designated by the same reference numerals. In this example, a sample and hold circuit 9 is provided in place of the peak detection circuit 4 in the circuit of FIG. The configuration is such that the signal is supplied to the laser diode 1 by. A recording gate signal (WG) is applied to the sample hold circuit 9, and in the playback mode, the sample hold circuit 9 enters the sample mode, forming a normal closed loop, and the light intensity of the laser diode 1 during playback is constant. Control is performed so that On the other hand, in the recording mode, the sample and hold circuit 9 enters the hold mode and holds the detected output value of the diode 2 immediately before recording, so that the reproduction current immediately before recording flows to the laser diode 1. During recording, a constant current 1o is added to this reproduction current according to data "1" or "O", and the resultant current flows through the laser diode 1 as a recording current.

This conventional circuit utilizes the fact that although the current versus light output characteristic of the laser diode shown in FIG. 7 fluctuates due to temperature changes, its slope (amount of change) is constant. Since the reproduction current is controlled by a normal closed loop, the light intensity of the laser diode 1 in the reproduction mode is controlled to a predetermined value and changes as shown by the 0Δ mark in FIG.

By adding a constant current IO to this current during recording, a constant light intensity can be obtained even during recording.

In the light intensity control circuit configured in this way, since no servo is applied to the recording current, no start-up time is required, but it is assumed that the slope of the current vs. light output characteristic is constant. Therefore, a normal DRAW (Direct Read Af) that uses a λ/4 plate to prevent the return light from the disk from returning to the laser diode
There is no problem with the optical system (ter Write), but there is a scoop (SCOOP,
5elf C0uDled 0ptical Pick
In an optical system in which there is a pronounced I will not be able to hold it.

Further, normally, the light intensity of the laser diode 1 is controlled by detecting the backward emitted light of the laser diode 1.
When there is a scoop, the light intensity of the backward emitted light is no longer proportional to that of the forward emitted light of the laser diode 1, so the light intensity of the laser diode 1 is controlled by detecting the backward emitted light of the laser diode 1. It has been found that stable control cannot be achieved when this is done.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a light intensity control circuit that can stably control the light intensity of a light source even in a pickup with a scoop and achieves high-speed response. With the goal.

The light intensity control circuit according to the present invention includes a system that detects the light intensity of at least the forward emitted light of the light source and controls the light intensity of the light source to be constant by using this detection output during reproduction, and a system that controls the light intensity of the light source to be constant during recording or recording. The configuration includes two control systems: a system that detects the peak value of the detection output at the time of erasing, and a system that controls the peak value of the light intensity of the light source based on this peak value.

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

FIG. 1 is a block diagram showing one embodiment of the present invention,
Functional blocks equivalent to those in FIG. 6 are indicated by the same reference numerals. In the figure, in addition to a photodiode 2 that detects the light intensity of the backward emitted light of the laser diode 1, a photodiode 2 that detects the light intensity of the backward emitted light of the laser diode 1 is used as a means for detecting the light intensity of the emitted light of the laser diode 1, which is a light source. A photodiode 12 is provided to detect the intensity. This photodiode 12 is provided not inside the case of the laser diode 1 but inside the optical system. The detection current of the photodiode 12 is converted into a voltage by an IV conversion circuit 13 and supplied to a peak detection circuit 14 . The peak detection circuit 14 detects the peak value of the output voltage of the l-V conversion circuit 13 and supplies it to the sample bold circuit 19 . As the peak detection circuit 14, one with a well-known circuit configuration can be used, but the circuit configuration already applied by the present applicant (Utility Application No. 1986-5)
2679 specification), that is, the peak detection error caused by the voltage VIE of the peak detection transistor, can be completely eliminated by passing the same current flowing through the peak detection transistor to the level shift diode or transistor. By using a peak detection circuit designed to compensate for detection errors, high-speed and stable peak detection can be achieved.

An inverted signal (WG) of the recording gate signal is applied to the sample and hold circuit 19, and the sample and hold circuit 1
9 is in a sample mode in the recording mode, and performs a hold operation during playback. The output of the sample hold circuit 19 becomes a comparison input of the comparison circuit 15. A reference voltage Vrer2 from a reference voltage source 16 is supplied to the comparison circuit 15 as a reference input. The error voltage, which is the comparison output of the comparison circuit 15, is converted into a current by the V-1 conversion circuit 17, and then accelerated to a recording current 1o flowing through the laser diode 1 during recording via a current limiting circuit 18.

The current limiting circuit 18 limits the control current based on the detected current of the photodiode (front monitor) 12 to about 1/10 of the total current flowing through the laser diode 1. In other words, the correction loop using the front monitor is
This is to correct variations in the current lamp light output characteristics due to the scoop, non-proportional parts of the light intensities of the rear emitted light and front emitted light, or temperature variations at the mold bone oscillator level in the case of high frequency superimposition. Therefore, the dynamic range of the control current may be about 1/10 of the total current.

As is clear from the above description, in this embodiment, the reproduction current correction loop (first control circuit) using the rear monitor (photodiode 2) shown in FIG.
The configuration is such that a recording current correction loop (second control circuit) using a photodiode 12) is added.

Next, the circuit operation of the light intensity control circuit according to the present invention having such a configuration will be explained.

In the recording mode (or recording/erase mode), during playback including the ID part reading period, the sample hold circuit 9
is in the sample mode, so the reproduction current correction loop by the rear monitor controls the light intensity of the laser diode 1 to be constant based on the detected current of the photodiode 2, and one sample and hold circuit is in the hold mode. Therefore, the recording current (or recording/erasing current) based on the detection current of the photodiode 12 is held.

On the other hand, during recording (or recording/erasing), the ripple hold circuit 19 enters the sample mode, so the peak detection circuit 1
Laser diode 1 based on the peak value detected in 4
Control is performed so that the peak value of the light intensity is constant, and the sample-and-hold circuit 9 is in the hold mode, so the reproduction current based on the current detected by the photodiode 2 is held. In addition, records (or records/
At the time of erasing), the sample and hold circuit 9 holds the reproduction current immediately before recording, so that a current obtained by adding a fixed current (constant current 1o) to this reproduction current flows as a recording (or recording/erasing) current. Current limit circuit 18
photodiode 12 within a finite range limited by
The current to be controlled is adjusted based on the detected current ζ).

In this way, during recording (or recording/erasing), the peak value of the detection output of the photodiode 12 is detected, and based on this peak value, the peak value of the light intensity of the laser diode 1 in the recording (or recording/erasing) section is determined. By controlling this, the light intensity can be stably controlled even in a pickup with a scoop.

Furthermore, by limiting the control range of the current limiting circuit 18, the following effects can be obtained. That is, even if the photodiode 12 provided in the optical system accidentally interrupts the optical path during adjustment, the laser diode 1 will not be destroyed because the correction loop's control current value t11 is small. Furthermore, since the control range is narrow, a relatively small control gain is sufficient, and the nervolube by the front monitor can be designed over a wide band. Furthermore, since most of the light intensity 1 odor of recording 1tii is determined by the fixed current IO, the rise of the light intensity during recording is very rapid, as shown in FIG. Furthermore, the ripple hold circuit 19 does not respond to the light intensity during playback, but instead holds the value at the time of recording, which is also a factor in speeding up, and the steady value is reached in the equivalent of 1320 to 30 μsec. Stable and fast response.

In the erasing mode, by controlling the data applied to the switching circuit 8 so that the logic "1" state continues, the laser diode 1 can continuously emit an erasing light beam.

FIG. 3 is a block diagram showing another embodiment of the present invention, in which only essential parts are shown. In this embodiment, recording (or recording/erasing) is performed in response to a recording gate signal (WG).
A constant pulse width T (for example, 10 μsec
A timing pulse generation circuit 20 that generates a pulse having a certain degree of intensity) and a switch 21 that opens (turns on) in response to the pulse generated from the circuit 20 are provided, and a timing pulse generation circuit 20 that generates a pulse having a certain degree of From constant time 1:]
The configuration is such that the DC voltage Va is superimposed by T on the error voltage of the comparator circuit 15.

According to this, it is possible to further improve the responsiveness of the rising edge during recording (or recording/erasing), and the loop response is approximately 10 to 20 μs.
This means that it can be improved to stabilize at a steady value equivalent to ec.

In each of the above embodiments, the light intensity during reproduction is controlled based on the detection output of the photodiode 2 that detects the light intensity of the rear emitted light. It is also possible to perform control based on the detection output of the diode 12, and the same effects as in each of the above embodiments can be obtained.
υ is rejected.

As explained above, according to the present invention, the servo system that controls the light intensity during reproduction to be constant and the peak value of the light intensity during recording (or recording/erasing) to be constant. Since the control during recording is performed based on the light intensity of the forward emitted light from the light source, even a pickup with a scoop can stably control the light intensity.

Furthermore, if the dynamic range of the recording current correction loop is limited, even if the forward emitted light is interrupted for some reason, it is unlikely that the laser diode will be destroyed. The rise in light intensity during recording can be made very fast.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the rising state of light intensity in response to data input during recording in the circuit of FIG. 1, and FIG. 3 is a block diagram showing an embodiment of the invention. 4 is a block diagram showing an example of a conventional circuit, and FIG. 5 is a waveform showing the rising state of light intensity in response to data input during recording in the circuit of FIG. 4. 6 is a block diagram showing another example of the conventional circuit, and FIG. 7 is a diagram showing the current versus light output characteristics of the diode. Explanation of symbols of main parts

Claims (2)

[Claims] (1) A light intensity control circuit for a light source in an optical information recording/reproducing device, which includes a detection means for detecting the light intensity of at least forward emitted light of the light source, and a detection means for detecting the light intensity of the light source at the time of reproduction based on the detection output of the detection means. a first control circuit that controls the light intensity of the light source to be constant; a first control circuit that detects a peak value of the detection output of the detection means during recording or recording/erasing, and based on this peak value, a peak value of the light intensity of the light source; A light intensity control circuit comprising: a second control circuit for controlling the light intensity control circuit; (2) The detection means includes first and second photodetectors that detect the respective light intensities of the rear emitted light and the front emitted light of the light source, and the first control circuit detects the light intensity of the rear emitted light and the front emitted light of the light source, respectively. The second control circuit controls the light intensity of the light source based on the detection output of the second photodetector, respectively, based on the detection output of the second photodetector.
The light intensity control circuit described in .