JPS59231747A - Driving circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To ensure the uniform quality of reproduced information signals over the entire area of a disk by controlling the average light emission power of a semiconductor laser with the output of a potentiometer which detects the disk radius and therefore increasing said light emission power toward the outer circumference of the disk and linearly to the disk radius. CONSTITUTION:The power supply of -VEE is supplied to a potentiometer 5 from a laser driving circuit via a terminal A; while the voltage linear to the radius of a disk 1 emerges at an output terminal B as an optical head 3 moves toward the radius of the disk 1. This voltage is used to the reference voltage to decide the average light emission power of a semiconductor laser 6. Then the light emission power given from the rear face of the laser 6 is received by a photodiode 7 to obtain a current linear to the light emission power. This current is converted into the voltage by a light emission power detecting resistance 11. This voltage is used as the reference voltage. For this purpose, the light emission power of the laser 6 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor laser drive circuit in an information recording and reproducing apparatus such as a recordable video disc player.

[Background of the invention]

Conventionally, a recording thin film is formed by vapor-depositing rl+, low oxide on a disk substrate, and by irradiating this recording thin film with a laser beam modulated by an information signal, information is recorded as a change in the reflectance of the recording thin film. There is known an apparatus that records a signal, then irradiates it with a weak laser beam, reads the change in reflectance of the recording thin film, and reproduces the information. When recording/reproducing television signals using this device, the number of revolutions of the disc should be set to 1 to facilitate still image or frame-by-frame playback.
8□00γpm iC is set so that exactly one revolution of the dial corresponds to one frame of the television signal.

Furthermore, the change in reflectance of the recording thin film mentioned above depends on the energy irradiated per unit area.

It is known that if the energy is too small, the change in reflectance will be small, leading to severe deterioration of the reproduced information signal, whereas if the energy is too large, the recorded dots will spread out, increasing high-order distortion of the information signal.

However, as mentioned above, in devices that record and reproduce television signals, the number of revolutions of the disk is kept constant, so the recording linear velocity is greater at the outer circumference of the disk than at the inner circumference. When irradiating the disc, the recording conditions change depending on the radius of the disc, resulting in the problem that uniform and good information signals cannot be reproduced over the entire disc.

[Purpose of the invention]

The object of the present invention is to solve the above-mentioned problems.

It is an object of the present invention to provide a semiconductor laser drive circuit that provides approximately the same recording and reproducing conditions over the entire area of a disk.

[Summary of the invention]

In order to achieve the above object, the present invention detects the disk radius using a potentiometer, creates a reference value for a circuit that controls the average light emission power of a semiconductor laser from the output of the potentiometer, and calculates the average light emission power as a function of the disk radius. The original energy per unit area irradiated onto the disk is made uniform over the entire disk area by linearly increasing the energy toward the outer periphery.

[Embodiments of the invention]

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

FIG. 1 is a diagram showing means for detecting the inner and outer peripheral positions of the disk, and FIG. 2 is a diagram showing the relationship between the output voltage of the position detecting means and the disk radius.

1 is a disk, 2 is a disk rotation motor, 3 is an optical head, 4 is an optical head moving device, and 5 is a potentiometer. One end of the potentiometer 5 is grounded, and a terminal A in the figure is supplied with a power of 1EE from a laser drive circuit to be described later.

Therefore, as shown in FIG. 2, as the optical head 6 moves in the radial direction of the disk, a voltage linear in the radius of the disk appears from the output terminal B of the position detection means.

FIG. 6 is a specific example of a laser drive circuit according to the present invention,
FIG. 4 is a diagram showing the relationship between the light emission power of the semiconductor laser and the disk radius. 6 is a semiconductor laser, 7 is a photodiode, 8)'; j-VER power supply, 9 is a buffer, and 10 is a variable attenuator.

11 is a light emitting power detection resistor, 12 is an operational amplifier, and 16 is L.
PF, 14 is a voltage-current conversion transistor, and 15 is a voltage-current conversion transistor.

This is a laser modulation circuit.

First, the operation when recording information signals on a disc will be explained. The output of the position detecting means is input to terminal B in the figure, and is supplied to variable attenuation 710 via buffer 19. The switch provided in the variable attenuator 10 is closed by an external control signal supplied from the terminal C, that is, the voltage supplied from the terminal B appears at the positive phase input terminal of the operational amplifier 12. This voltage is the reference voltage (hereinafter referred to as V
rgf). Operational amplifier 12, LPFl
3. Voltage-to-current conversion transistor button 14° The semiconductor laser 6, the photodiode 7, and the light emitting power detection resistor 11 form a negative hood loop, and the photodiode 7 receives the light emitting power from the rear surface of the semiconductor laser 6, and emits light. ) A linear current is obtained through the hoe and converted into a voltage by the light-emitting nozzle detection resistor 11, and the light-emitting nozzle of the semiconductor laser 6 is controlled so that this voltage becomes the reference voltage Vraf described above. .

Further, a laser modulation circuit 15 composed of a clamp circuit and a voltage-current conversion transistor causes a modulation current to flow through the semiconductor laser 6 in accordance with an information signal inputted from a terminal, thereby modulating the emission power of the semiconductor laser 6. Therefore, as shown in Figure 4, the light emitting power in the recording mode has an average value that follows changes in the reference value Vref and has a linear relationship with the disk radius ((a) in the figure), and the modulation by the information signal remains at a constant level regardless of the radius of the disk.

Next, the case of reproducing the recorded information signal will be explained. At this time, the switch in the variable attenuator 10 is opened by the external control signal from the terminal C. Therefore, the reference voltage Vraf at the positive phase input terminal of the operational amplifier 12 is set to By dividing by two resistors, the value is set lower than that during recording, and since the terminal is in an unmanned state, no current flows through the semiconductor laser 61C through the laser modulation circuit 15, and the emission power of the semiconductor laser 6 is reduced. According to 7, the level is low as shown in (b) of Fig. 4.

In Figure 4, P is the recorded power at the innermost Aya.

Q indicates the recording power for external use.

According to this embodiment, information signals are recorded and reproduced by always irradiating laser light under the same conditions regardless of the inner or outer circumference of the disk.

The quality of the reproduced information signal is maintained uniform.

〔Effect of the invention〕

As explained above, according to the present invention, uniform and good image quality can be obtained over the entire disk area.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the disk position detection means, FIG. 2 is a characteristic diagram showing the relationship between the potentiometer σ output voltage and the disk radius, and FIG. 3 is a circuit diagram showing an embodiment of the laser drive circuit. FIG. 4 is a characteristic diagram showing the relationship between the light emission of the semiconductor laser according to the present invention and the disk radius. 5...Potentiometer 6...Semiconductor laser 7...Photodiode 11...Emission power detection resistor 12...Operation amplifier 15...Laser modulation circuit 1st closed 2nd picture 31 Fig. 4-80 TEN SUKUTINE % CLOSED P

Claims (1)

[Claims] 1. Record the information signal by modulating a semiconductor laser according to the information signal, irradiating the modulated laser beam C onto the disk, and then irradiating the disk with a weak laser beam to record the information signal. A semiconductor laser driving circuit of a device for reproducing information signals generated by the semiconductor laser includes a detector for detecting light emitting power disposed opposite to an IC on the rear surface of the semiconductor laser, and a detector for detecting light emitting power from the detector. A circuit that inputs a signal and controls a substantially DC component of the emitted light power to a reference value, a circuit that modulates the emitted power of the semiconductor laser according to the information signal, and means for detecting the inner and outer circumferential positions of the disk. A semiconductor laser drive circuit comprising means for controlling a reference value of a circuit for controlling a substantially direct current component of the light emission power based on the output of the inner and outer circumferential position detecting means. 2. The semiconductor laser drive circuit according to claim 1, wherein the reference value of the circuit for controlling the substantially DC component of the emitted light power is in a relationship that is generally linear with the radius of the disk and increases in the direction of the outer circumference. 1. A semiconductor laser drive circuit characterized in that the semiconductor laser drive circuit is controlled so that