JP2005346874A - Superimposing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain the undesirable radiation of a superimposed frequency and its harmonic component. <P>SOLUTION: The component of a modulation frequency (modulation signal) is added to the reference voltage (current) of a superimposing circuit 2, and consequently a frequency control signal, which corresponds to a setting frequency + a modulation signal frequency, is generated in the output of a frequency setting circuit 2a. In an oscillation circuit 2b in which, the frequency control signal is inputted, an oscillation frequency becomes a signal whose frequency periodically changes at a speed corresponding to a modulation frequency in a range represented by an equation "f*VM/VREF", wherein f is a setting frequency, VREF is a reference voltage, and VM is the amplitude of a modulation signal. The frequency-modulated frequency thus generated is applied to a laser diode 5 by an output circuit 4. The frequency modulation changes in frequency with time, and therefore its frequency spectrum has broadness. The whole energy is the same, and accordingly power at each frequency decreases, and a level of undesirable radiation is consequently reduced. A level of undesirable radiation at a high frequency wave is also reduced due to the similar effect. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a superposition circuit, and more particularly to a superposition circuit that drives a laser element by a high frequency superposition method.

  In recent years, optical disk technology has undergone significant development. The optical disk can be reproduced in a non-contact manner with the optical disk by laser light. Although there was a CD as an optical disk, it is now widely accepted by the market due to its small size and high-speed accessibility. Under such circumstances, DVD (Digital Video Disc) has appeared. The DVD technology, like the CD technology, irradiates an optical disk with laser light and obtains data by the brightness of the reflected light, and is widely accepted in the market.

  FIG. 8 is a configuration diagram of a conventional auto power control (APC) circuit for driving a laser element, in which reference numeral 11 is a superposition circuit, 11a is an oscillator, 11b is an output circuit, 12 is a filter, 13 is an APC circuit, 14 Indicates a laser diode (LD), and 15 indicates a photodiode (PD).

  Laser light output from the laser diode 14 is not only irradiated onto a DVD (digital video disk) but also received by the photodiode 15. Light is converted into an electrical signal by the photodiode 15, and at this time, an electrical signal corresponding to the amount of laser light is obtained. In response to this electrical signal, the APC circuit 13 is controlled so that the amount of emitted laser light is constant.

  The laser diode 14 includes a single mode laser and a multimode laser. In the single mode laser, the oscillation frequency is likely to fluctuate due to the temperature characteristics of the laser itself and the return light noise, and a mode jump is likely to occur. There is a drawback that the light output fluctuates and noise is likely to occur. On the other hand, laser diodes that emit light in multimode have been developed, but have disadvantages such as low reliability and high cost.

  Therefore, in general, a method of obtaining a multi-mode laser beam by driving a single-mode laser diode using a high-frequency superposition method has been adopted. The high-frequency superposition method utilizes the fact that a (single mode) laser diode emits light in multimode at the start of operation. In particular, if the laser diode is a self-excited oscillation type, it tends to be multimode at the time of startup. As a circuit for achieving the harmonic superposition method, a rising state is continued by applying a high frequency signal from the outside to the laser diode by the superposition circuit shown in FIG. 8, and laser light including a plurality of wavelengths is emitted.

  Therefore, by using the harmonic superposition method, it is possible to use a single mode laser diode as if a multimode laser diode is used. Since laser diodes that emit laser light in a single mode are widely available on the market as general-purpose products, the harmonic superposition method is now an effective means.

  The filter 12 is inserted for the purpose of suppressing unnecessary radiation generated by the high-frequency fundamental wave and harmonics generated by the superposition circuit 11 via the power source.

  FIG. 9 is a block diagram showing a conventional superposition circuit. In the figure, reference numeral 21 is a superposition circuit, 22 is an oscillator, 22a is a frequency setting circuit, 22b is an oscillation circuit, 22c is a frequency setting element, 23 is an output circuit, and 24 is A racer diode is shown.

  The superposition frequency of the superposition circuit 22 is high enough not to affect the reproduction data, and is set to a frequency at which stable multimode oscillation is achieved and noise characteristics and the like are improved. For this reason, the superimposing circuit 22 includes a frequency setting circuit 22a for setting a frequency and an oscillation circuit 22b.

  The frequency setting circuit 22a can normally set a predetermined oscillation frequency by the resistance element 22c so that the set frequency can be varied. An oscillation circuit 22b that receives this output signal (= frequency control signal) generates an oscillation signal having a frequency corresponding to the frequency control signal. The generated oscillation signal having the frequency is applied to the laser diode 24 by the output circuit 23. Further, a method of directly giving a frequency control signal (voltage, current) by DA or the like is also used.

JP 2000-216484 A

  However, the high frequency superposition frequency is usually several hundred MHz or more, and in addition to this, harmonics of n times the fundamental wave (an integer of N> = 2) are generated. A high frequency of several hundred MHz or more is likely to be radiated out of a system such as a light pickup, for example, and therefore it is necessary to suppress unnecessary radiation. Therefore, if measures such as connecting a filter to the output section or power supply of the superimposing circuit are taken, there is a problem that the circuit related to the high frequency superimposing method becomes large and expensive.

  Further, in Patent Document 1, the harmonic characteristic of n times is suppressed by limiting the frequency characteristic of the output circuit, but there is a problem that even if the harmonic component can be suppressed, the fundamental wave component cannot be suppressed. there were.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a superposition circuit capable of suppressing unnecessary radiation of a superposition frequency and its harmonic components.

  The present invention has been made to achieve such an object, and the invention according to claim 1 is a superposition circuit for driving a laser element by a high frequency superposition method in accordance with a reference signal and a set frequency. A frequency setting circuit that generates a frequency control signal, an oscillation circuit that generates a superimposed signal based on the frequency control signal from the frequency setting circuit, a modulation signal is input, and the superimposed signal corresponds to the modulation signal frequency And a modulation signal input means for frequency-modulating the frequency at a high speed, and the frequency-modulated frequency from the oscillation circuit is applied to the laser element. (Corresponding to Fig. 1)

According to a second aspect of the present invention, in the first aspect of the present invention, a frequency setting element for changing the setting frequency of the frequency setting circuit is provided, and a reference for setting a frequency in the frequency setting circuit is provided. It is characterized in that the signal is changed. (Corresponding to Fig. 1)
According to a third aspect of the present invention, in the first or second aspect of the invention, the modulation signal input means includes addition means for adding the modulation signal to the reference signal. (Corresponding to Fig. 1)

  According to a fourth aspect of the present invention, in the invention according to the first or second aspect, the modulation signal input means connects a variable resistance element in series to the frequency setting element, and the resistance value of the variable resistance element Is varied by the modulation signal. (Corresponding to Fig. 2)

  According to a fifth aspect of the present invention, in the first aspect of the present invention, the modulation signal input means includes an adder between the frequency setting circuit and the oscillation circuit, so that the frequency control signal directly The modulation frequency signal is added. (Corresponding to Fig. 3)

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein a triangular wave is used for the modulation frequency signal.

  According to a seventh aspect of the invention, there is provided the voltage dividing circuit according to any one of the first to sixth aspects, wherein the voltage of the reference signal is divided, and a modulation signal generating circuit connected to the voltage dividing circuit. The ratio between the reference signal and the voltage or current for applying the modulation is kept constant. (Corresponding to Fig. 4)

  The invention according to claim 8 is the invention according to claim 3, wherein a frequency dividing circuit and a level conversion circuit are provided between the adding means and the oscillator to control an oscillation frequency. . (Corresponding to Fig. 5)

  According to the present invention, a frequency setting circuit that generates a frequency control signal according to a reference signal and a set frequency, an oscillation circuit that generates a superimposed signal based on the frequency control signal from the frequency setting circuit, and a modulation signal Since it is provided with modulation signal input means for temporally frequency-modulating the input superimposed signal at a speed corresponding to the modulation signal frequency, the frequency-modulated frequency from the oscillation circuit is applied to the laser element. By modulating the superposition frequency, unnecessary radiation of the fundamental wave and harmonic components can be remarkably suppressed, and countermeasures against unnecessary radiation are facilitated.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram for explaining a first embodiment of a superposition circuit according to the present invention, in which reference numeral 1 is a superposition circuit, 2 is an oscillator, 2a is a frequency setting circuit, 2b is an oscillation circuit, and 2c is a frequency setting element. (Resistance), 3 is an adder, 4 is an output circuit, and 5 is a laser diode.

  The superimposing circuit 2 of the present invention is for driving a laser element by a high frequency superimposing method. A modulation frequency component (modulated signal) is added to the reference voltage (current) of the superimposing circuit 2 via an adder 3 to superimpose the superposed circuit 2. The frequency is modulated. Here, the superposition frequency means the frequency of the high frequency signal applied to the laser diode 5 by the superposition circuit 2.

  The superposition circuit 2 has an adder 3 for adding a reference signal and a modulation signal, and an output signal of the adder 3 as an input signal, and a frequency setting for generating a frequency control signal corresponding to the set frequency and the modulation signal frequency. An oscillator 2 comprising a circuit 2a and an oscillation circuit 2b that inputs the frequency control signal from the frequency setting circuit 2a and generates a temporally frequency-modulated signal at a speed corresponding to the modulation signal frequency. The frequency-modulated frequency from the oscillator 2 is applied to the laser diode 5. Further, a frequency setting element 2c for changing the setting frequency of the frequency setting circuit 2a is provided, and the reference signal for setting the frequency in the frequency setting circuit 2a is changed.

  That is, by adding a modulation frequency component (modulation signal) to the reference voltage (current) of the superposition circuit 2, a frequency control signal corresponding to the set frequency + modulation signal frequency is generated at the output of the frequency setting circuit 2a. In the oscillation circuit 2b having this as an input, assuming that the oscillation frequency is the set frequency f, the reference voltage VREF, and the amplitude of the modulation signal is VM, the time is temporally at a speed corresponding to the modulation frequency in the range of f * VM / VREF. The signal changes in frequency, that is, a frequency-modulated signal. The generated frequency-modulated frequency is applied to the laser diode 5 by the output circuit 4.

  Since the frequency of frequency modulation changes with time, the frequency spectrum has a spread. However, since the overall energy is the same, the power at each frequency decreases and as a result the level of unwanted radiation decreases. For the harmonics, the unnecessary radiation level is reduced by the same effect.

  2 is a block diagram for explaining a second embodiment of the superposition circuit of the present invention. In the figure, reference numeral 2d denotes a variable resistance element, and other components having the same functions as those in FIG. It is. In the second embodiment, the variable resistance element 2d is inserted in series with the frequency setting element (resistor) 2c except for the adder 3 in the first embodiment, and the resistance value is varied according to the modulation frequency. If the set frequency f, the set resistance RSET, and the series resistance change from 0 to RM, a signal whose frequency changes with time at a speed corresponding to the modulation frequency in the range of the frequency at the time of REST and the frequency at the time of RSET + RM. As a result, a frequency modulation signal is obtained in the same manner as described above, and the same effect is obtained.

  When the superimposing circuit 2 is integrated, the frequency setting element (resistor) 2c is usually externally attached. Therefore, whether the modulation is normally performed by measuring the voltage, current, and resistance value of this terminal. Can be determined. In the case of integration, whether the integrated circuit is acceptable or not can be determined without directly measuring the superimposed frequency. As described above, since the superposition frequency is as high as several hundred MHz, this method can greatly reduce the equipment required for inspection and the inspection time.

  FIG. 3 is a block diagram for explaining Embodiment 3 of the superposition circuit according to the present invention. In the figure, reference numeral 2e denotes an adder, and other components having the same functions as those in FIG. It is. In the third embodiment, an adder 2e is newly provided between the frequency setting circuit 2a and the oscillation circuit 2b of the oscillator 2 except for the adder 3 provided in the preceding stage of the oscillator 2 in the first embodiment. It is.

  By providing an adder 2e between the frequency setting circuit 2a and the oscillation circuit 2b, the modulation frequency signal is added directly to the frequency control signal. This is also the same operation as in the first embodiment. The effect of can be obtained. In this case, DA or the like may be used for the frequency setting circuit.

  If you change the superposition frequency so that it becomes a triangular wave in time, such as by using a triangular wave for the modulation frequency signal, the superposition frequency that changes in time becomes uniform in time, so the spread frequency spectrum becomes uniform, As a result, the unnecessary radiation level is also reduced uniformly. The problem with unwanted radiation is usually at its highest level, so uniform attenuation is most effective.

  As described above, since the superposed frequency is determined by conditions such as data and laser, when changing the frequency by frequency modulation, the frequency change must be controlled and stabilized.

  FIG. 4 is a block diagram for explaining a fourth embodiment of the superposition circuit of the present invention. In FIG. 4, reference numeral 6 denotes a voltage dividing circuit, 7 denotes a modulation signal generating circuit, and other components having the same functions as in FIG. Are denoted by the same reference numerals. The fourth embodiment includes a voltage dividing circuit 6 that divides a reference voltage in the first embodiment, and a modulation signal generating circuit 7 that inputs a signal from the voltage dividing circuit 6 and outputs a modulation signal to the adder 3. It is a thing.

  In this way, by dividing the reference voltage by the voltage dividing circuit 6 and determining the amplitude of the modulation frequency by the modulation signal generating circuit 7, even if the reference voltage varies, the ratio of the frequency modulation width to the superimposed frequency Is configured so that it can always be kept constant.

  FIG. 5 is a block diagram for explaining a fifth embodiment of the superposition circuit of the present invention. In FIG. 5, reference numeral 8 denotes a frequency dividing circuit, 9 denotes a level conversion circuit, and other components having the same functions as those in FIG. Are given the same reference numerals. In the fifth embodiment, a frequency dividing circuit 8 and a level converting circuit 9 are provided between the adder 3 and the oscillator 2 in the first embodiment.

  That is, the fifth embodiment has a configuration for generating a modulation frequency composed of the frequency dividing circuit 8 and the level converting circuit 9, and since the oscillation frequency is controlled, a stable frequency can be obtained. By using this to generate a modulation frequency using the frequency dividing circuit 8, a stable modulation frequency can be produced with a small circuit.

  The frequency dividing circuit 8 divides the oscillation frequency, and the level conversion circuit 9 sets it to a predetermined level, which is used as a modulation signal. Here, the oscillation frequency f increases when the modulation signal is +, decreases when the modulation signal is −, and its frequency width is Δf. Then, as shown in FIG. 6, when the modulation signal is +, the oscillation frequency increases (f + Δf), so the output cycle of the frequency dividing circuit 8 is shortened, and the modulation signal is inverted at a predetermined frequency. -. In this case, since the oscillation frequency decreases (f−Δf), the cycle of the output of the frequency dividing circuit 8 becomes long. Let this difference be Δt. As a result, the duty of the modulation signal is shifted by Δt. This deviation amount is determined by the ratio between the oscillation frequency and the frequency to be changed. When the rate of changing the oscillation frequency is small, Δt is small enough to be ignored, so that there is no particular problem.

  Further, if the output of the level conversion circuit 9 is a triangular wave, the output of the frequency dividing circuit 8 is equal to the average value Avh and Avl of the modulation signal in the Hi and Lo periods as shown in FIG. 7 (in FIG. 7, Zero) and the average frequency of the oscillation frequency is also the same (= f in the figure), and the problem that the output of the frequency dividing circuit 8 is shifted in duty is eliminated.

It is a block diagram for demonstrating Example 1 of the superposition circuit of this invention. It is a block diagram for demonstrating Example 2 of the superposition circuit of this invention. It is a block diagram for demonstrating Example 3 of the superposition circuit of this invention. It is a block diagram for demonstrating Example 4 of the superposition circuit of this invention. It is a block diagram for demonstrating Example 5 of the superposition circuit of this invention. FIG. 10 is a diagram (part 1) illustrating an oscillator signal, a divided signal, and a modulation signal in the fifth embodiment illustrated in FIG. 5; FIG. 7 is a diagram (part 2) illustrating an oscillator signal, a divided signal, and a modulation signal in the fifth embodiment illustrated in FIG. 5; It is a block diagram of the auto power control (APC) circuit which drives the conventional laser element. It is a block diagram which shows the conventional superposition circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Superimposition circuit 2 Oscillator 2a Frequency setting circuit 2b Oscillation circuit 2c Frequency setting element 2d Variable resistance element 2e Adder 3 Adder 4 Output circuit 5 Laser diode 6 Voltage dividing circuit 7 Modulation signal generating circuit 8 Frequency dividing circuit 9 Level converting circuit 11 Superimposing circuit 11a Oscillator 11b Output circuit 12 Filter 13 APC circuit 14 Laser diode (LD)
15 Photodiode (PD)
21 Superposition circuit 22 Oscillator 22a Frequency setting circuit 22b Oscillation circuit 22c Frequency setting element 23 Output circuit 24 Racer diode

Claims (8)

In the superposition circuit for driving the laser element by the high frequency superposition method,
A frequency setting circuit that generates a frequency control signal according to a reference signal and a set frequency, an oscillation circuit that generates a superimposed signal based on the frequency control signal from the frequency setting circuit, and a modulation signal that is input, A modulation signal input means for frequency-modulating the signal temporally at a speed corresponding to the modulation signal frequency;
A superposition circuit, wherein a frequency-modulated frequency from the oscillation circuit is applied to the laser element.   2. The superimposing circuit according to claim 1, wherein a frequency setting element for changing the setting frequency of the frequency setting circuit is provided, and a reference signal for setting a frequency in the frequency setting circuit is changed. .   The superimposing circuit according to claim 1, wherein the modulation signal input means includes addition means for adding the modulation signal to the reference signal.   3. The superimposing circuit according to claim 1, wherein the modulation signal input unit connects a variable resistance element in series to the frequency setting element, and varies a resistance value of the variable resistance element according to the modulation signal. .   2. The modulation signal input means according to claim 1, wherein an adder is provided between the frequency setting circuit and the oscillation circuit, and the modulation frequency signal is directly added to the frequency control signal. Superposition circuit.   6. The superimposing circuit according to claim 1, wherein a triangular wave is used for the modulation frequency signal.   A voltage dividing circuit for dividing the voltage of the reference signal; and a modulation signal generating circuit connected to the voltage dividing circuit, and maintaining a constant ratio between the reference signal and a voltage or current for applying the modulation. The superposition circuit according to any one of claims 1 to 6, 4. The superimposing circuit according to claim 3, wherein a frequency dividing circuit and a level converting circuit are provided between the adding means and the oscillator to control an oscillation frequency.

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