JP4083388B2 - Electronic device, light output control device, and electronic apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic device, a light output control circuit using the same, and an electronic device, and more particularly to an electronic device for controlling and outputting output light of a light emitting element, a light output control circuit using the same, and an electronic device. .
[0002]
[Prior art]
Digital copying machines, laser printers, optical disk devices, optical communication devices, and the like perform the formation of an electrostatic latent image, the writing of information to an optical disk, and the transmission of information by using the action of light. In such an apparatus, a semiconductor laser is used as a light source. Since semiconductor lasers are small and can be directly modulated at high speed by a drive current, they are widely used as light sources for these devices in recent years. For example, in a printer or the like, as shown in FIG. 16, the bias current of the light emitting element 12 is controlled by a sample hold circuit 301, transistors Q11 and Q12, resistors R11 and R12 based on the detection signal detected by the light receiving element 12. In this case, the same problem occurs. However, in the bias current control, the light response of the light emitting element is faster when it is flowed more in a copying machine or printer using a photoconductor. However, it is necessary to control the output light to a desired value with high accuracy.
[0003]
However, since the optical output and forward current characteristics of the semiconductor laser change remarkably with temperature, there is a problem when trying to set the optical output of the semiconductor laser to a desired value. In order to solve this problem, various APC (automatic power control) circuits, that is, automatic power control circuits have been proposed.
[0004]
Such an APC circuit is disclosed in, for example, Japanese Patent Laid-Open No. 2-205379. Japanese Laid-Open Patent Publication No. 2-205379 describes a semiconductor laser drive / control system using an optical / electrical negative feedback loop. That is, an optical / electrical negative feedback loop that monitors the optical output of the semiconductor laser with a light receiving element and controls the forward current of the semiconductor laser so that the received light signal proportional to the optical output of the semiconductor laser is equal to the emission level command signal. Thus, the optical output of the semiconductor laser is controlled. Use of the APC circuit having such a configuration is promising in terms of high speed, high accuracy, and high resolution.
[0005]
Conventionally, such an optical output control circuit has a semiconductor laser and a light receiving element configured as individual elements, and is connected to an APC circuit formed on a circuit board with a wiring pattern or a harness, or is received by a semiconductor laser. In general, an element is built in and connected to an APC circuit formed on a circuit board by a wiring pattern or a harness.
[0006]
[Problems to be solved by the invention]
However, in such a control method, when the optical / electrical negative feedback loop is to be operated at high speed, the frequency characteristics between the optical output of the semiconductor laser and the received light signal monitoring it are not good. There is. In such a case, there is a problem that a desired optical waveform may not be obtained, such as an optical output overshoot.
[0007]
In addition, in the bias current control circuit of the light emitting element using the optical / electrical negative feedback loop, the light receiving element output and the sample hold circuit, when the light output of the light emitting element is controlled with high accuracy, Since the linearity with the light receiving signal of the light receiving element is not good, there is a problem that the desired light output may not be controlled particularly during bias current control.
[0008]
The present invention has been made in view of the above points, and an object thereof is to provide an electronic device capable of forming a feedback loop with high accuracy and high speed, a light output control circuit using the electronic device, and an electronic apparatus.
[0009]
[Means for Solving the Problems]
The electronic device of the present invention includes a light receiving unit that outputs a detection signal corresponding to incident light from a light emitting element, and a compensation unit that compensates the detection signal so that the detection signal changes linearly with respect to the incident light. If, by comparing the detection signal compensated by the compensation section and the input signal, there is a configuration in which a control circuit unit that controls a forward current of the light emitting element on the basis of the comparison result.
[0010]
The compensation unit performs compensation based on a detection signal detected by the light receiving unit.
[0011]
The compensation unit further includes a calculation unit that performs a predetermined calculation on the detection signal detected by the light receiving unit, and a compensation signal generation unit that generates a compensation signal according to the calculation result of the calculation unit and superimposes the detection signal on the detection signal It consists of.
[0012]
In the present invention, the light receiving unit, the compensation unit, and the control circuit unit are configured integrally or on the same integrated circuit.
[0013]
According to the present invention, the compensation unit compensates the detection signal detected by the light receiving unit according to the incident light so as to change linearly with respect to the incident light, so that the amount of light emitted from the light emitting unit is not affected. The emitted light quantity can be controlled linearly.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a block diagram of an electronic device of the first embodiment of the present invention.
[0015]
The light output control circuit 1 according to this embodiment includes an electronic device 11 and a light emitting element 12. The electronic device 11 detects a part of the light emitted from the light emitting element 12, compensates the detection signal, controls the light emission instruction signal by the compensation signal, and supplies it to the light emitting element 12.
The electronic device 11 includes a light receiving element 21 corresponding to the light receiving unit in the claims, a linearity compensation circuit 22 corresponding to the compensation unit in the claims, and a comparison amplifier circuit 23 corresponding to the control circuit unit. Yes. The light receiving element 21, the linearity compensation circuit 22, and the comparison amplifier circuit 23 are formed on the same semiconductor chip 31 as shown in FIG. The semiconductor chip 31 is stored in the package 32. From the package 32, at least an input terminal Tin, an output terminal Tout, and a power supply terminal Ts are extended.
[0016]
In the present embodiment, the light receiving element 21 and the comparison amplification circuit 23 are formed on the same semiconductor chip 31. However, the light reception element 21 and the comparison amplification circuit 23 are configured by separate semiconductor chips 31 and accommodated in the same package. You may make it do.
[0017]
FIG. 3 shows a block diagram of an electronic apparatus according to a modification of the first embodiment of the present invention. In the figure, the same components as in FIG.
[0018]
In this modification, the light receiving element 21 is mounted on the semiconductor chip 41, the electronic device 22 is mounted on the semiconductor chip 42, the semiconductor chip 41 and the semiconductor chip 42 are mounted on the substrate 43, and stored in the same package 32. It is said that.
[0019]
In the modification shown in FIG. 3 as well, the distance between the light receiving element and the comparison amplifier circuit 23 is within the same package 31, so that it is sufficiently smaller than the wiring length and parasitic capacitance, and is the same as that of the configuration shown in FIG. The effect of.
[0020]
A driving voltage is applied to the light receiving element 21 from the power supply terminal Ts. The light receiving element 21 receives a part of the light from the light emitting element 12 and supplies a detection signal corresponding to the amount of received light to the linearity compensation circuit 22. The linearity compensation circuit 22 compensates the detection signal so that the characteristic of the detection signal with respect to the incident light of the light receiving element 21 changes linearly.
[0021]
FIG. 4 is a diagram showing the characteristics of the monitor current with respect to the incident light of the light receiving element.
[0022]
In general, the monitor current efficiency, which is the ratio between the light output of the light emitting element 12 and the detection signal of the light receiving element 21, for example, the monitor current, may be constant regardless of the magnitude of the light output as shown by the solid line in FIG. Ideal. However, the actual light receiving element 21 does not have a constant monitor current efficiency particularly in a region where the light output is small. That is, the linearity of the monitor current is bad.
[0023]
This is due to the structure of the light receiving element 21, etc., and the monitor current efficiency decreases as the light output decreases as shown by the broken line in FIG. 4 due to the structure of the light receiving element 21 and the like. As shown by the alternate long and short dash line, the monitor current efficiency may increase as the light output decreases.
[0024]
In order to reduce the monitor current efficiency as the light output becomes smaller as shown by the broken line in FIG. 4, when the control is performed with the small light output P0, only a current smaller than the monitor current that should flow originally flows. The light output value is controlled to be larger than the light output P0.
[0025]
In addition, when the monitor current efficiency increases as the light output decreases as shown by the one-dot chain line in FIG. 4, when attempting to control the small light output P0, a current larger than the monitor current that should flow originally flows. As a result, the light output value is controlled to be smaller than P0.
[0026]
The linearity compensation circuit 22 compensates the characteristic peculiar to the light receiving element 21 shown by the broken line or the alternate long and short dash line in FIG. 4 so as to become the characteristic shown by the solid line in FIG.
[0027]
On the other hand, a light emission level command signal is input to the input terminal Tin. The light emission level command signal input to the input terminal Tin is supplied to the comparison amplifier circuit 23.
[0028]
The comparison amplifier circuit 23 controls the light emission level command signal according to the detection signal from the linearity compensation circuit 22. The signal controlled by the comparison amplifier circuit 23 is output from the output terminal Tout. The light emitting element 12 is connected to the output terminal Tout. The light emitting element 12 is composed of, for example, a semiconductor laser, a constant voltage is applied to the anode, and the cathode is connected to the output terminal Tout.
[0029]
A drive current corresponding to the output signal of the output terminal Tout flows through the light emitting element 12. The light emitting element 12 emits light corresponding to the drive current. Light emitted from the light emitting element 12 is supplied to a light incident target such as a photosensitive drum, an optical disk, or an optical fiber, and part of the light is incident on the light receiving element 21.
[0030]
The light emitting element 12, the light receiving element 21, the linearity compensation circuit 22, and the comparison amplification circuit 23 form an optical / electrical negative feedback loop, and the comparison amplification circuit 23 outputs the light output of the light emitting element 12 induced in the light reception element 21. The detection signal proportional to the proportional photocurrent is compared with the light emission level command signal, and the forward current of the light emitting element 12 is controlled based on the comparison result so that the light reception signal and the light emission level command signal are equal.
[0031]
Next, details of the linearity compensation circuit 22 will be described with reference to the drawings.
[0032]
FIG. 5 is a diagram showing a specific example of the linearity compensation circuit according to the first embodiment of the present invention.
[0033]
First, the linearity compensation circuit 32 of the electronic device 31 shown in FIG. 5 is a circuit for compensating the characteristic shown by the alternate long and short dash line in FIG. The constant current source 33 is connected between a connection point between the light receiving element 21 and the comparison amplifier circuit 23 and the terminal Ts2, and generates a predetermined current according to a voltage applied to the terminal Ts2.
[0034]
The constant current generated by the constant current source 33 is preset according to the amount of light output from the light emitting element 12, and is compensated so that the detection signal from the light receiving element 21 becomes a predetermined level with a predetermined amount of incident light. Current is output.
[0035]
FIG. 6 is a block diagram showing a modification of the linearity compensation circuit according to the first embodiment of the present invention.
The linearity compensation circuit 42 of the electronic device 41 shown in FIG. 6 is a circuit for compensating for the characteristic indicated by the broken line in FIG. The constant current source 43 is connected between the connection point between the light receiving element 21 and the comparison amplification circuit 23 and the ground, and draws a predetermined current from the current supplied from the light reception element 21 to the comparison amplification circuit 23.
[0036]
The constant current generated by the constant current source 43 is preset according to the amount of light output from the light emitting element 12, and is compensated so that the detection signal from the light receiving element 21 becomes a predetermined level with a predetermined amount of incident light. Current is output.
[0037]
The linearity compensation circuits 32 and 42 of the electronic devices 31 and 41 shown in FIGS. 5 and 6 are effective only for a predetermined output light amount, but the compensation amount is set according to the detection signal of the light receiving element 12. By making it variable, it is possible to effectively compensate with various output light amounts.
[0038]
FIG. 7 shows a configuration diagram of a second modification of the linearity compensation circuit according to the first embodiment of the present invention.
[0039]
The linearity compensation circuit 52 of the electronic device 51 illustrated in FIG. 7 includes a current detection unit 53, a division unit 54, and a current generation circuit 55. The current detection unit 53 detects the detection signal from the light receiving element 21, that is, the monitor current Idp, and supplies a signal corresponding to the monitor current to the division unit 54.
[0040]
FIG. 8 shows a circuit configuration diagram of the division unit.
[0041]
As shown in FIG. 8, the division unit 54 includes resistors R1 and R2, an operational amplifier 56, and a multiplier 67, and an output obtained by dividing the detection signal from the current detection unit 53 is obtained. The output of the division unit 54 is supplied to the current generation unit 55. For this reason, the output of the division unit 53 is different depending on the detection signal of the current detection unit 53.
[0042]
The current generator 55 generates a current according to the output of the divider 54. The current generated by the current generator 55 is added to the detection signal of the light receiving element 21, that is, the monitor current Idp, and is supplied to the comparison amplifier circuit 23.
[0043]
In FIG. 8, when the input of the multiplier 57 is X, the multiplier is kY, and the output is Z ′,
Z '= kXY
From the relationship
I2 = Z ′ / R2 = k × (XY / R2)
Since I1 = Z / R1 and I1 + I2 = 0, the output X is
X = − (1 / k) × (Z / Y)
It becomes. That is, an output that is inversely proportional to Y is obtained as the output X.
[0044]
In FIG. 8, when a current that is inversely proportional to the monitor current is generated and used as the compensation current I, the compensation current becomes a large value when the monitor current is small, and becomes smaller as the monitor current becomes larger and the monitor current is sufficiently large. Therefore, it is possible to compensate for the linearity of the monitor current by adding or subtracting this current to the monitor current.
[0045]
According to this modification, the compensation amount is varied according to the monitor current, and the compensation can be performed with the optimum compensation amount according to the output light amount of the light emitting element 12.
[0046]
FIG. 9 shows a configuration diagram of a third modification of the linearity compensation circuit according to the first embodiment of the present invention. In the figure, the same components as those in FIG.
[0047]
The electronic device 61 shown in FIG. 9 has a configuration in which a logarithmic operation unit 63 is provided instead of the division unit 54.
[0048]
FIG. 10 shows a circuit configuration diagram of the logarithmic operation unit.
[0049]
The logarithmic operation unit 63 includes a resistor R3, an operational amplifier 64, and a diode 65, and outputs a logarithmic value corresponding to a predetermined coefficient β of the detection signal from the current detection unit 53. For this reason, the output of the logarithmic calculation unit 63 is different depending on the detection signal of the current detection unit 53. The signal output from the logarithmic operation unit 63 is supplied to the current generation unit 55.
[0050]
The current generator 55 generates a current corresponding to the output of the logarithmic calculator 63. The current generated by the current generator 55 is added to the detection signal of the light receiving element 21, that is, the monitor current Idp, and is supplied to the comparison amplifier circuit 23.
[0051]
In the logarithmic operation unit 63, the forward current If of the diode 65 is
If = Is.exp (Vf / VT)
Here, VT = kT / q, Is: reverse saturation voltage of diode D, k: Boltzmann constant, q: electron charge, VT: thermal voltage. Summarizing the natural logarithm of this If,
Vf≈VT (lnIf-lnIs)
It becomes. The input of the operational amplifier 64 is an imaginary earth.
Vf = -V0 = -VT (lnIf-lnIs)
Therefore, the output V0 is a negative logarithmic output with respect to the input V1, and becomes a large value when the monitor current is small, and decreases as the monitor current increases and can be regarded as almost zero when the monitor current is sufficiently large. A configuration capable of generating a current can be realized, and the characteristic indicated by the broken line in FIG. 4 can be corrected.
[0052]
In the above modification, the detection signal of the light receiving element 21, that is, the monitor current is calculated and compensated in an analog manner. However, the compensation may be performed using a conversion table.
[0053]
FIG. 11 shows a configuration diagram of a fourth modification of the linearity compensation circuit according to the first embodiment of the present invention.
[0054]
The linearity compensation circuit 72 of the electronic device 71 of this modification includes an A / D (analog / digital) converter 73, a conversion table 74, and a D / A (digital / analog) converter 75. The detection signal of the light receiving element 21, that is, the monitor current is converted into digital data by the A / D converter 73. The conversion table 74 stores digital data after compensation of the detection signal of the light receiving element 21. The conversion table 74 is referred to using the digital data converted by the A / D converter 73 as an address, and compensated data is output. Data output from the conversion table 74 is converted into an analog signal by the D / A converter 75 and supplied to the comparison amplifier circuit 23.
[0055]
According to this modification, the compensation amount is varied according to the monitor current, and the compensation can be performed with the optimum compensation amount according to the output light amount of the light emitting element 12. Further, compensation can be performed freely by changing the data in the conversion table 74, so that compensation can be performed accurately.
[0056]
According to the first embodiment, the light receiving element 21, the linearity compensation circuit 22, and the comparison amplifier circuit 23 are configured integrally or on the same integrated circuit, and are configured to directly receive an optical signal in the integrated circuit. The optical / electrical negative feedback loop can be configured without being affected by the speed reduction due to wiring, the deterioration of frequency characteristics due to impedance components and parasitic capacitance, and the noise mixed into the wiring.・ Electric negative feedback loop can be realized. In addition, since there are no external wiring such as elements, harnesses, or optical fibers, a high-speed, high-precision optical / electrical negative feedback loop can be realized at low cost. In addition, the optical output can be controlled with high accuracy by compensating the linearity of the efficiency of the received light signal by the linearity compensation circuit 22.
[0057]
In the present embodiment, the detection signal of the light receiving element 21, that is, the monitor current is compensated, but the light emission level command signal may be compensated.
[0058]
FIG. 12 is a block diagram of the second embodiment of the present invention. In the figure, the same components as in FIG.
[0059]
The light output control circuit 100 of the present embodiment is different from the first embodiment in the configuration of the electronic device 101. The electronic apparatus 101 according to the present embodiment has a configuration in which a linearity compensation circuit 102 is provided between a terminal Tin to which a light emission level command signal is input and the comparison amplifier circuit 23.
[0060]
The linearity compensation circuit 102 has a configuration in which the compensation amount is opposite to that of the linearity compensation circuit 22 and compensates the light emission level command signal.
[0061]
FIG. 13 shows a configuration diagram of the third embodiment of the present invention. In the figure, the same components as in FIG.
[0062]
The light output control circuit 110 of the present embodiment is different from the first embodiment in the configuration of the electronic device 111. The electronic device 111 according to the present embodiment includes, in addition to the light / electrical negative feedback loop including the light emitting element 12, the light receiving element 21, the linearity compensation circuit 22, and the comparison amplification circuit 23, the order of the light emitting elements 12 according to the light emission level command signal. The structure which added the current converter 112 which drives a directional current is shown.
[0063]
According to the present embodiment, since the forward current of the light emitting element 12 can be driven by the light level command signal by the current converter 112, the light emitting element 12 can be driven at high speed.
[0064]
In the present embodiment, the detection signal of the light receiving element 21, that is, the monitor current is compensated, but the light emission level command signal may be compensated.
[0065]
FIG. 14 shows a configuration diagram of the fourth embodiment of the present invention. In the figure, the same components as those in FIGS. 12 and 13 are denoted by the same reference numerals, and the description thereof is omitted.
[0066]
The light output control circuit 120 of this embodiment compensates the light emission level command signal by the linearity correction circuit 102 and supplies it to the comparison amplifier circuit 23, and drives the light emitting element 12 by the current converter 1112. According to the present embodiment, the same operation and effect as the third embodiment can be obtained.
[0067]
FIG. 15 is a block diagram of the fifth embodiment of the present invention. In the figure, the same components as in FIG.
[0068]
The light output control circuit 200 of the present embodiment is different from the first embodiment in the configuration of the electronic device 201. The electronic device 201 includes a light receiving element 21, a current conversion circuit 202, a linearity compensation circuit 203, and an amplification circuit 204. The current conversion circuit 202 draws current from the light receiving element 21 into the light emission level command signal from the terminal Tin. The linearity compensation circuit 203 compensates the current drawn from the light receiving element 21 to the current conversion circuit 202 so that the characteristic shown in FIG. 4 becomes the characteristic shown by the solid line.
[0069]
The amplifier circuit 204 draws a current corresponding to the voltage at the connection point between the light receiving element 21 and the linearity compensation circuit 203 from the output terminal Tout and drives the light emitting element 12.
[0070]
The light controlled by the light output control circuit is a digital copying machine, a laser printer, a photosensitive drum, an optical disk device, an optical disk via an optical system, and an optical communication device. The light is emitted to the optical fiber and the surrounding space.
[0071]
The light output control circuit is also effective when driving the light emitting element 12 through a sample and hold circuit as shown in FIG.
[0072]
【The invention's effect】
As described above, according to the present invention, the compensation unit compensates the detection signal detected by the light receiving unit in accordance with the incident light so as to change linearly with respect to the incident light, thereby causing the light emitting unit to emit light. Since the amount of emitted light can be controlled linearly regardless of the amount of light, the light output can be controlled with high accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram of a first embodiment of the present invention.
FIG. 2 is a configuration diagram of an electronic device according to a first embodiment of the present invention.
FIG. 3 is a configuration diagram of a modified example of the electronic device according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating a characteristic of a monitor current with respect to incident light of a light receiving element.
FIG. 5 is a diagram showing a specific example of the linearity compensation circuit according to the first embodiment of the present invention.
FIG. 6 is a configuration diagram of a modification of the linearity compensation circuit according to the first embodiment of the present invention.
FIG. 7 is a configuration diagram of a second modification of the linearity compensation circuit according to the first embodiment of the present invention.
FIG. 8 shows a circuit configuration diagram of a division unit.
FIG. 9 is a configuration diagram of a third modification of the linearity compensation circuit according to the first embodiment of the present invention;
FIG. 10 is a circuit configuration diagram of a logarithmic operation unit.
FIG. 11 is a configuration diagram of a fourth modification of the linearity compensation circuit according to the first embodiment of the present invention;
FIG. 12 is a configuration diagram of a second embodiment of the present invention.
FIG. 13 is a block diagram of a third embodiment of the present invention.
FIG. 14 is a configuration diagram of a fourth embodiment of the present invention.
FIG. 15 is a block diagram of a fifth embodiment of the present invention.
FIG. 16 is a circuit configuration diagram of an optical output control circuit using a sample hold circuit as an output.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Light output control circuit 11 Electronic device 12 Light emitting element 21 Light receiving element 22 Linearity compensation circuit 23 Comparison amplification circuit

Claims (6)

A light receiving unit that outputs a detection signal corresponding to incident light from the light emitting element ;
A compensator for compensating the detection signal so that the detection signal changes linearly with respect to the incident light;
Comparing the detection signal compensated by the compensation section and the input signal, the electronic apparatus characterized by a control circuit unit that controls the forward current of the light emitting element on the basis of the comparison result. The electronic device according to claim 1, wherein the compensation unit performs compensation based on the detection signal detected by the light receiving unit .   The compensation unit performs a predetermined calculation on the detection signal detected by the light receiving unit, generates a compensation signal according to the calculation result of the calculation unit, and superimposes the compensation signal on the detection signal The electronic device according to claim 1, further comprising a generation unit.   4. The electronic device according to claim 1, wherein the light receiving unit, the compensation unit, and the control circuit unit are configured integrally or on the same integrated circuit. 5. And the light emission element,
A light receiving unit that receives a part of the light emitted from the light emitting element and outputs a detection signal corresponding to the incident light;
A compensator for compensating the detection signal so that the detection signal changes linearly with respect to the incident light;
An optical output control circuit comprising: a control circuit unit that compares an input signal with the detection signal compensated by the compensation unit and controls a forward current of the light emitting element based on a comparison result . In an electronic device that irradiates a predetermined irradiation target with light,
A light-emitting element that emits light to be irradiated to the irradiation target according to an input signal;
A light receiving unit that receives a part of the light emitted from the light emitting element and outputs a detection signal corresponding to the incident light;
A compensator for compensating the detection signal so that the detection signal changes linearly with respect to the incident light;
Electronic apparatus, characterized in that a control circuit unit for comparing the detection signal is compensated by the input signal and the compensation unit, and controls a forward current of the light emitting element on the basis of the comparison result.

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