JPH03171436A - Laser modulating circuit - Google Patents

Abstract

PURPOSE:To set the peak and bottom of a light output individually by controlling the output currents of a high level laser driving circuit and a low level laser driving circuit with the outputs of a peak comparator and a bottom comparator. CONSTITUTION:Light power is modulated into a square wave, whose peak power and bottom power are supplied by the high level laser driving circuit 1a and low level laser driving circuit 1b. A peak value held by a peak holding circuit 6, on the other hand, is compared with the set value of the peak by the peak comparator 8 and applied as a control signal to the high level laser driving circuit 1a to output a current so that the peak value equals the set value, thereby setting the peak power of a laser diode 3. Further, the bottom value held by a bottom holding circuit 7, on the other hand, is compared by the bottom comparator 9 with the set value of the bottom level and applied as a control signal to the low level laser driving circuit 1b, so that the bottom power of the laser diode 3 is set similarly. Consequently, the peak and bottom of the light power can be set individually.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc device, and particularly to a laser modulation circuit that can separately set high and low levels of optical output during laser modulation.

[Prior Art] FIG. 4 shows an example of a laser modulation circuit used in a conventional optical disc device.

The output current of the laser drive circuit 1 is supplied to the laser diode 3 via a resistor.

The light emission of the laser diode 3 is modulated by the switching circuit 2.

In other words, part of the current supplied by the laser drive circuit 1 is E
Bypassed by a transistor whose base current is controlled according to the FM signal, the current flowing through the laser diode 3 is modulated by the EFM signal.

The photodiode 4 receives the light emitted by the laser diode 3, passes a current according to the intensity of the received light, and causes a voltage drop across the variable resistor 5. The voltage appearing across the variable resistor 5 is RC. The voltage is averaged by the circuit and applied to the laser drive circuit 1 as a control voltage.

In this way, the current flowing through the laser diode 3 is controlled so that the voltage across the variable resistor 5 is constant.

[Problems to be Solved by the Invention] In the conventional laser modulation circuit described above, the average optical output is set by the variable resistor 5, and the degree of modulation when optically modulated is set by the variable resistor of the switching circuit 2.

The peak and bottom of the optical output appear above and below the average optical output, and in order to set the peak of the optical output, the variable resistor 5 and the variable resistor of the switching circuit 2 must be set together, which is time-consuming. It took.

Furthermore, even if the duty ratio of the EFM signal 3 was changed, the peak and bottom of the optical output changed, so readjustment was necessary.

This DJJ was developed in order to solve the above problem, and provides a laser modulation circuit that can separately set the peak and bottom of the optical output without being affected by the duty ratio of the EFM signal. With the goal.

[Means for Solving the Problems] A laser modulation circuit of the present invention selects the output currents of a high-level laser drive circuit and a low-level laser drive circuit according to a modulation signal and flows them to a laser diode. a light output detector that detects the light emission output of the light output detector, a peak hold circuit that holds the peak value of the light output detector, a bottom hold circuit that holds the bottom value of the light output detector, and an output of the peak hold circuit. a peak comparator that compares the peak set value with the peak set value;
A bottom comparator is provided to compare the output of the bottom hold circuit with a bottom set value, and the output currents of the high-level laser drive circuit and the low-level laser drive circuit are determined by the respective outputs of the peak comparator and the bottom comparator. It is configured to control.

[Function] 3. The laser modulation circuit modulates the optical power into a square wave as shown in FIG. 2, but the peak power and bottom power are supplied by the high-level laser drive circuit and the low-level laser drive circuit, respectively.

The intensity of the light output is detected by a light output detector, and its peak value and bottom value are held in a peak hold circuit and a bottom hold circuit, respectively.

The peak value held in the peak hold circuit is compared with a peak set value by a peak comparator, and the peak comparator outputs a signal that determines whether the peak value is larger or smaller than the set value.

The output of the peak comparator is averaged and applied as a control signal to a high-level laser drive circuit, and the high-level laser drive circuit outputs a current so that the peak value is equal to a set value. In this way, the peak power of the laser diode is set.

Further, the bottom value held in the bottom bold circuit is compared with the bottom set value by a bottom comparator, and the bottom comparator outputs a signal that determines whether the bottom value is larger or smaller than the set value.

The output of the bottom comparator is averaged and applied as a control signal to the low level laser drive circuit, and the low level laser drive circuit outputs a current so that the bottom value is equal to the set value. In this way, the bottom power of the laser diode is set.

The peak power and bottom power thus set are selected according to the modulation signal, and the output of the laser diode is modulated.

"Example" Hereinafter, practical examples of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a laser modulation circuit which is a first practical example of the present invention.

In the figure, 1a and 1b are a high-level laser drive circuit and a low-level laser drive circuit, which supply current to the laser diode 3 via a resistor.

6 1] is a Schmidt 1~ circuit, and outputs two outputs that are inverted to each other according to the input, and each output is connected to the base of each of the two l-transistors of the switching circuit 1o. Supply current.

Reference numeral 12 denotes an optical output detector which converts the current flowing through the laser diode 3 into a voltage and applies the peak voltage to the inputs of the peak hold circuit 6 and the bottom hold circuit 7.

The peak hold circuit 6 holds the output voltage peak value of the optical output detector 12 in a capacitor, and outputs the voltage to the peak comparator 8 through the operational amplifier output terminal.

The bottom hold circuit 7 holds the output voltage bottom value of the optical output detector 12 in a capacitor, and outputs the voltage from the operational amplifier output terminal to the bottom comparator 9.

The internal comparator of the peak comparator 8 compares the output voltage of the peak hold circuit 6 with the reference voltage set by the variable resistor, and outputs a high or low voltage depending on the magnitude relationship between the two, and the output voltage is It is averaged by a resistor and a capacitor and controls the high-level laser drive circuit 1a.

An internal comparator in the bottom comparator 9 compares the output voltage of the bottom hold circuit 7 with a reference voltage set by a variable resistor, and outputs a high or low voltage depending on the magnitude relationship between the two, and the output voltage is It is averaged by a resistor and a capacitor and controls the low level laser drive circuit 1b.

Next, the operation of the laser modulation circuit will be explained.

In the laser modulation circuit, the optical power is modulated into a square wave as shown in FIG. It is output by flowing .

High level laser drive circuit 1a and low level laser drive circuit 1b can be selected by Schmitt circuit l1 or E F M r
This is done by switching the switching circuit 10 according to the = sign.

The optical output of the laser diode 3 is proportional to the magnitude of the flowing current, and is detected by the optical output detector 12 by differentially amplifying the voltage across the resistor 7 connected in series with the laser diode 3, and its peak value and The bottom value is peak hold circuit 6 and bottom hold circuit 7, respectively.
is held.

Peak hold times li! The peak value held in the peak value 86 is compared with a peak set value by a peak comparator 8, and the comparator of the peak comparator 8 outputs different levels depending on the magnitude of the peak value with respect to the set value.

The output of the peak comparator is averaged by a resistor and a capacitor, and is applied as a control signal to the high-level laser drive circuit 1a.
a outputs a current so that the peak value is equal to the set value. In this way, the peak power of the laser diode 3 is set.

In addition, the bottom value held in the bottom bold circuit 7 is compared with the bottom setting value by the bottom comparator, and the comparator of the bottom comparator 9 selects a level 8 which varies depending on the magnitude of the above-mentioned volume value with respect to the setting value. Output.

The above output of the bottom comparator 9 is averaged by a resistor and a capacitor and sent to the low level laser drive circuit 1b.
is added as a control signal to the low level laser drive circuit R.
lb outputs a current so that it becomes equal to the bottom value or the set value. In this way, the port 1 of the laser diode 3
-Mupawa is set.

The peak power and peak power set in this way are selected according to the modulation signal, and the optical output of the laser diode is modulated.

FIG. 3 is a diagram without showing the optical output detector of a laser modulation circuit according to a second embodiment of the present invention.

In the second embodiment, the light output detector 12 in the circuit shown in FIG. 1 is replaced with a light output detector 12 not shown in FIG. It is connected to a diode, and the other configurations are the same as in the first example.

In this embodiment, the light emitted from the laser diode is received by the photodiode 4, and the light output of the laser diode is detected by converting the current flowing through the photodiode 4 into a voltage.

Detecting the optical output using the photodiode 4 allows more accurate optical output setting.

Furthermore, in this embodiment, by arranging the photodiode 4 inside the pickup at a location away from the laser diode, the photodiode 4 is not affected by the heat generated by the laser diode, and is not affected by temperature changes caused by the heat generated by the laser diode itself. The intensity of the light emission can be detected immediately, making it possible to accurately set the peak and bottom of the optical power.

Note that the photodiode 4 needs to be a bin photodiode or the like, which has good response at the modulation frequency.

[Effects of the Invention] As described above, according to the laser modulation circuit of the present invention, the peak and bottom of the optical power can be set separately, making adjustment easy.

Further, since the peak and bottom of the optical output do not change even when the duty ratio of the EFM signal is changed by 4b to 11, there is no fear that the optical output of the laser diode will exceed the maximum rating and the laser diode will be destroyed.

Furthermore, as shown in the second embodiment, if the optical output is detected using a photodiode, the optical output can be set more accurately.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a laser modulation circuit according to a first embodiment of the present invention, FIG. 2 is a waveform diagram showing the optical power applied to the laser modulation circuit, and FIG. FIG. 4 is a circuit diagram showing a portion of the second embodiment, and FIG. 4 is a circuit diagram showing a conventional laser modulation circuit. 1a... High level laser drive circuit, 1b Low level laser drive circuit, 3... Laser diode, 4...
Photodiode, 6...Peak hold circuit, 7.
...Bottom hold circuit, 8...Peak comparator, 9.
...Bottom comparator, 10...Switching circuit, 11
...Schmitt circuit, 12...light output detector. 1 2 771W Figure 2

Claims (1)

[Claims] In a laser modulation circuit that selects output currents of a high-level laser drive circuit and a low-level laser drive circuit according to a modulation signal and sends them to a laser diode, the light output detector detects the light emission output of the laser diode; a peak hold circuit that holds the peak value of the optical output detector; a bottom hold circuit that holds the bottom value of the optical output detector; a peak comparator that compares the output of the peak hold circuit with a peak setting value; and the bottom hold circuit. A bottom comparator is provided to compare the output of the peak comparator and the bottom set value, and the output currents of the high-level laser drive circuit and the low-level laser drive circuit are controlled by the respective outputs of the peak comparator and the bottom comparator. The constructed laser modulation circuit.