JPH07192879A - Illuminance correcting amplifier - Google Patents

Abstract

PURPOSE:To provide an illuminance correcting amplifier for driving a fluorescent lamp or the like at a constant illuminance. CONSTITUTION:A light receiving means 1 receives the light and converts it into the electrical signal. High-side switch means 6, 8 compare the electric information with the high-side reference voltage, and in the case where the electric information is higher than the high-side reference voltage, output the reference pulse signal, which is output from an oscillator 10, as the high-side pulse signal. Low-side switching means 7, 9 compare the electric information with the low-side reference voltage, and in the case where the electric information is lower than the low-side reference voltage, output the reference pulse signal as the low-side pulse signal. An up-down counter 11 counts down with the high-side pulse signal, and counts up with the low-side pulse signal, and outputs the count signal of PCM code. A D/A converting means 12 converts the count signal from the direct current to the alternating current, and output the control signal. An inverter means 21 outputs the driving signal, which is controlled by the control signal, to a light emitting means 22, and the light emitting means 22 emits the light at a constant illuminance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called correction amplifier, and more particularly to an illuminance correction amplifier for controlling electric power for keeping the illuminance of a light source constant.

[0002]

2. Description of the Related Art In a so-called image processing system, the system captures an original image of a subject from a camera and performs image processing based on the original image data. then,
It is important to capture the original image with a clearer contrast ratio (contrast) of the subject in order to produce good results.

In a conventional image processing system or the like, a halogen lamp or the like has been used as illumination for illuminating a subject. The characteristics of this halogen lamp are shown in FIG. As shown in FIG. 5A, the illuminance of the halogen lamp is substantially constant even if the temperature rises due to long-time irradiation. As described above, it is common knowledge in image processing to use illumination having good temperature characteristics in which the illuminance does not change even when irradiated for a long time.

However, depending on the shape of the subject, it may be difficult to irradiate all the surfaces of the subject with uniform light by using a halogen lamp or the like having a strong directivity of light. For example,
This is the case when the spoon is the subject. That is,
When a spoon is the subject, there are irregularities in the opening of the spoon, which is the subject, and subtle undulations in the handle. Therefore, in an image processing system installed in a manufacturing plant for spoons, etc. that examines foreign substances on the surface of the spoon and defects in manufacturing, when a light source with a strong directivity such as a halogen lamp is irradiated, the shadow part due to the unevenness and undulations Will increase. Therefore, the shaded portion is erroneously detected as a foreign substance or the like, or is undetectable.

Therefore, in the image processing system for inspecting a subject such as a spoon which is highly undulating, a fluorescent lamp has been used as a light source. Fluorescent lamps have weak directivity and are optimal as an illuminating device that irradiates a surface having a complicated shape with a light amount of light that is as uniform as possible.

[0006]

However, the image processing system using a fluorescent lamp as a light source has a problem that it is difficult to obtain a stable light amount for a long time due to the temperature characteristics of the fluorescent lamp.

FIG. 5B shows the temperature characteristics of the fluorescent lamp.
As shown in FIG. 5B, the illuminance of the fluorescent lamp fluctuates sharply with time and has no correlation with the temperature. Therefore, if a fluorescent lamp is used as it is in an image processing system, its illuminance is not stable, and therefore important setting values of the system such as a binary level finely adjusted for detecting foreign matters must be frequently changed. I won't.

In order to solve this problem, an object of the present invention is to provide an illuminance correction amplifier which can supply a corrected drive power to a light source with unstable illuminance and can maintain a stable illuminance. is there.

[0009]

In order to achieve the above object, the illuminance of irradiated light may be measured and a correction power corresponding to the increase or decrease may be supplied to the fluorescent lamp.

Therefore, the illuminance correction amplifier according to claim 1 inputs the illuminance voltage and a light receiving means (1) for generating an illuminance voltage having a potential difference corresponding to the illuminance of incident light.
Comparing means (6, 7, 8, 9, VR ₄ , for comparing both the high-side reference voltage and the low-side reference voltage set lower than the high-side reference voltage with the illuminance voltage and outputting a corresponding control signal.
VR ₅ ) and comparison means (6, 7, 8, 9, VR ₄ , VR
₅ ) A driving means (21) for outputting a driving signal corresponding to the control signal output by the driving means, and a light emitting means (22) for emitting light at an illuminance corresponding to the driving signal output by the driving means (21) are provided. (6, 7, 8, 9, VR ₄ , VR ₅ ) is
When the illuminance voltage is lower than the low-side reference voltage, the control signal is changed to increase the illuminance by the drive signal, and when the illuminance voltage is higher than the high-side reference voltage, the control signal is changed to decrease the illuminance by the drive signal. And has a non-control range in which the control signal is not changed when the illuminance voltage is higher than the low-side reference voltage and lower than the high-side reference voltage.

The illuminance correction amplifier according to claim 2 is the illuminance correction amplifier according to claim 1, wherein the comparison means sets the high-side voltage setting means (V) for setting the high-side reference voltage.
R ₄ ), low-side voltage setting means (VR ₅ ) for setting the low-side reference voltage, and oscillator (1
0) and the reference pulse signal generated by the oscillator (10) are input, the illuminance voltage is compared with the high side reference voltage, and a high side pulse signal is output when the illuminance voltage is higher than the high side reference voltage. The side switching means (6, 8) and the reference pulse signal generated by the oscillator (10) are input, the illuminance voltage and the low side reference voltage are compared, and when the illuminance voltage is lower than the low side reference voltage, the low side Low side switch means (7,
9) and the high-side pulse signal output from the high-side switch means (6, 8), the count signal is subtracted or added in the direction of decreasing the illuminance by the drive signal, and the low-side switch means (7, 9) outputs. The up-down counter (11) that adds or subtracts the count signal in the direction to increase the illuminance by the drive signal based on the low-side pulse signal and outputs the count signal, and the count signal output by the up-down counter (11) is D / A converted. D / A conversion means (1
2) and are provided.

[0012]

According to the invention described in claim 1, the following operations are performed. The light receiving means (1) generates an illuminance voltage having a potential difference corresponding to the illuminance of incident light. Comparison means (6,
7, 8, 9, VR ₄ , VR ₅ ) compares the illuminance voltage with both the high-side reference voltage and the low-side reference voltage set lower than the high-side reference voltage, and outputs a corresponding control signal. .
Specifically, when the illuminance voltage is lower than the low side reference voltage, the control signal is changed to increase the illuminance by the drive signal, and when the illuminance voltage is higher than the high side reference voltage, the illuminance by the drive signal is reduced. Change the control signal in the direction of
It has a non-control range in which the control signal is not changed when the illuminance voltage is higher than the low-side reference voltage and lower than the high-side reference voltage. The driving means (21) then compares the comparing means (6,
Drive signals are output corresponding to the control signals output by 7, 8, 9, VR ₄ , VR ₅ ). Therefore, the light emitting means (22)
Can emit light with illuminance corresponding to the drive signal output from the drive means (21).

According to the second aspect of the invention, it operates as follows. The high-side voltage setting means (VR ₄ ) sets the high-side reference voltage, and the low-side voltage setting means (VR ₅ ) sets the low-side reference voltage which is lower than the high-side reference voltage. The oscillator (10) generates a reference pulse signal having a constant frequency and supplies it to the high side switch means (6, 8) and the low side switch means (7, 9). The high side switch means (6, 8) receives the reference pulse signal generated by the oscillator (10) and compares the electric signal generated by the light receiving means (1) with the high side reference voltage. When the electric signal has a voltage higher than the high-side reference voltage, the reference pulse signal is output as the high-side pulse signal. Similarly, the low side switch means (7, 9) inputs the reference pulse signal generated by the oscillator (10) and compares the electric signal generated by the light receiving means (1) with the low side reference voltage. When the electric signal has a voltage lower than the low-side reference voltage, the reference pulse signal is output as the low-side pulse signal. The up / down counter (11)
The high-side pulse signal output by the high-side switch means (6, 8) counts up or counts up, and the low-side pulse signal output by the low-side switch means (7, 9) counts up or down. Then, a count signal which is a PCM code is output. The count signal is D / A converted to increase / decrease the illuminance in the direction of entering the non-control range. D / A conversion means (1
2) can D / A convert the count signal output from the up / down counter (11) and output a control signal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the illumination correction amplifier of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention. As shown in FIG. 1, the output signal of the silicon light receiving element 1 provided in the vicinity of the image processing camera is
Illumination correction amplifier 2 with shielded wire S to prevent noise
0 is input to the input terminal T ₀ . The silicon light receiving element 1 receives the light that has arrived by the light emission of the fluorescent lamp 22 and generates an electromotive force due to the photovoltaic effect at both ends thereof. Although this electromotive force is substantially proportional to the intensity of light, it does not necessarily have a linear relationship and may have a certain correlation between the amount of light received and the electromotive force. Silicon light receiving element 1
Since it functions as a photoelectric conversion element, an element that produces a photoelectric effect, such as a photoconductive sensor, a photodiode, or a phototransistor, can be used.

The illuminance correction amplifier 20 is constructed as follows. The input amplifier 2 amplifies the electric signal output from the silicon light receiving element 1 and outputs an illuminance voltage V _i . When there is a long distance from the silicon light receiving element 1 to the illuminance correction amplifier 20, the influence of external noise cannot be ignored, so a mounting technique such as a guard pattern is used. The amplification factor of the input amplifier 2 can be finely adjusted by the variable resistor VR ₁ . The buffer 3 buffers the illuminance voltage V _i , and the illuminance monitor terminal T ₁
Output to. The switch SW ₁ switches between the illuminance voltage V _i and the manual operation voltage V _m from the variable resistor VR ₂ to select the automatic mode (A) or the manual mode (M). Switch SW ₁ and switch SW ₂ are interlocked and are in automatic mode (mode to correct illuminance by illuminance correction amplifier)
Is switched to the A side, and in the manual mode (mode in which illuminance is not corrected and irradiation is performed with a manual setting value), the mode is switched to the M side. In manual mode, the variable resistance V
The amount of electric power supplied to the fluorescent lamp 22 is determined by R ₂ . The switches SW ₁ and SW ₂ and the variable resistor VR ₂ for manual illuminance adjustment are important operation parts for switching between manual / automatic operation, and thus are provided on a panel or the like for the convenience of the operator.

The differential amplifier 4 forms an inverting amplifier together with the resistors R _{1 to} R ₄ . The function of the differential amplifier 4 is to obtain the output V _i ′ by using the output of the switch SW ₁ as an inverting input and the offset voltage V _off defined by the variable resistor VR ₃ as a positive phase input. The amplifier 5 amplifies the output V _i ′ of the differential amplifier 4 and outputs the illuminance voltage V _i ″. The comparator 6 compares the reference voltage V _H of the variable resistor VR ₄ with the illuminance voltage V _i ″. Outputs the high voltage side detection signal.
The comparator 7 compares the reference voltage V _L of the variable resistor VR ₅ with the illuminance voltage V _i ″ and outputs a detection signal on the low voltage side. The NAND gates 8 and 9 function as a pulse supply switch. The oscillator 10 generates a reference pulse signal, and the reference pulse signal generated by the oscillator 10 has a frequency within a range in which the up / down counter 11 can operate.
It can be set appropriately. Generally, a higher oscillation frequency has better convergence characteristics. However, since the fluctuation cycle of the illuminance of the fluorescent lamp 22 is sufficiently larger than the frequency at which the oscillator can oscillate, it can be said that the correction characteristic does not change with the change of the oscillation frequency. The up / down counter 11 is
When a pulse is input to the count-up terminal U, it counts up by 1, and when a pulse is input to the count-down terminal D, it counts down by 1. The output of the NAND gate 8 for performing high-side correction is connected to the down-count terminal D of the up-down counter 11. The output of the NAND gate 9 for performing low-side correction is connected to the up-count terminal. The D / A converter 12 converts the output of the up / down counter 11 into an analog voltage. The amplifier 13 amplifies the output of the D / A converter 12 to a predetermined voltage. The switch SW ₂ is interlocked with the switch SW ₁ to select the automatic mode (A) or the manual mode (M). The buffer 14 forms a current amplifier together with the transistor Q and the resistor R ₅ . The resistor R ₆ has one end connected to the power supply voltage V _DD and the other end connected to the output terminal T ₃ , and converts a change in the output current into a voltage. The amplifier 15 amplifies this voltage and connects it to the output current monitor terminal T ₂ .

Furthermore, as an external device connected directly to the illuminance correction amplifier 20, an illuminance monitor M ₁ for monitoring the state of the lighting the operator is connected to the illuminance monitor terminal T _1.
An output current monitor M ₂ for monitoring the output current is connected to the output current monitor terminal T ₂ . The illuminance monitor M ₁ and the output current monitor M ₂ are provided not only for the convenience of the operator to monitor the operation of the system, but also for providing an alarm function for notifying an abnormal situation such as when the illuminance or the output current falls below a reference value. . The inverter 21 is connected to the output terminal T ₃ .

FIG. 2 shows an additional device required in the measurement environment for operating the illuminance correction amplifier 20. As shown in FIG. 2, in order to operate the illuminance correction amplifier 20, it is necessary to form a closed loop (feedback loop). A closed loop composed of this light and an electric system is formed by including a silicon light receiving element 1, an illuminance correction amplifier 20, an inverter 21 that drives a fluorescent lamp 22, and a fluorescent lamp 22. Further, a halogen lamp 23 is provided as auxiliary lighting. The power supply E _O is an illuminance correction amplifier 20 and an inverter 21.
Also, electric power is supplied to the halogen lamp 23. Measurement of illuminance itself, a silicon light receiving element 1 _-2, a luminometer M _3,
Done by.

Next, the operation will be described. In order to set the operation mode to the automatic mode in which the correction operation is valid, the switches SW ₁ and SW ₂ on the panel are switched to the A side.

First, the flow of signals to the up / down counter 11 will be described. The light incident on the silicon light receiving element 1 is converted into an electric signal corresponding to this amount of light. This electric signal becomes a differential input of the input amplifier 2 via the input terminal T _0, and an output V _i according to this potential difference is obtained. The function of the input amplifier 2 is mainly to perform impedance conversion and to amplify to the compatible voltage of the illuminance monitor by setting the variable resistor VR ₁ . The buffer 3 current-amplifies the input voltage V _i and supplies it to the illuminance monitor terminal T ₁ . The differential amplifier 4 receives the input signal V _i as an inverting input and sets the offset voltage V _off as a positive phase voltage. Then, the subtraction results of both of them are output as the output V _i ′. Therefore, the output V _i ′ has a relationship represented by | V _i ′ | = | illuminance voltage V _i −V _off |. The offset voltage V _off is for adjusting the offset level of the illuminance voltage V _i so that it becomes an optimum voltage value to be input to the comparators 6 and 7 when amplified by the amplifier 5. This offset voltage V
_off is adjusted by the variable resistor VR ₃ and has a value of 9 [V], for example. The output V _i 'is input to the amplifier 5,
The illuminance voltage V _i ″ is amplified (for example, 3.3 times) to a voltage value suitable for input to the comparator.

The control of the illuminance correction is determined by the detection unit composed of the comparators 6 and 7 and the variable resistors VR ₄ and VR ₅ . In this detection unit, a kind of window comparator that defines the operation range is formed. That is, when the input illuminance voltage V _i ″ is higher than the high-side reference voltage V _H adjusted by the variable resistor VR ₄ , the comparator 6 supplies the H level voltage as a detection signal to one terminal of the NAND gate 8. The other terminal of the NAND gate 8 is connected to the oscillator 1
Since the pulse signal is input from 0, the detection signal is H
Only when it is at the level, the NAND gate 8 outputs the count pulse. Similarly, the input illuminance voltage V _i ″
Is lower than the low-side reference voltage V _L adjusted by the variable resistor VR ₅ , the comparator 7 supplies the H level voltage as a detection signal to one terminal of the NAND gate 9. NAND
Since the pulse signal is also input from the oscillator 10 to the other terminal of the gate 9, the NAND gate 9 outputs the count pulse only when the detection signal is at the H level.

Next, in order to understand the operation around the up / down counter 11, the operation from the initial state will be described step by step. When the power of the illuminance correction amplifier 20 is turned on, the reset function works and the count value of the up / down counter 11 is 0.
Is. The output of the up / down counter 11 has a PCM code and is converted into an analog value by the D / A converter 12. This analog voltage is input to the buffer 14 via the switch SW ₂ . Therefore, current amplification according to this analog voltage is performed and output to the output terminal T ₃ . A control current terminal of the inverter 21 is connected to the fluorescent lamp 22 so as to output the output power according to the amount of input current.
Supply to.

Initially, the count value of the up / down counter 11 is 0, and there is almost no current output. Therefore, the fluorescent lamp 22 is dark. As long as the amount of light emission is small, the illuminance voltage V input to the comparators 6 and 7 via the silicon light receiving element 1
_i ″ is low and V _i ″ <V _L. At this time, the output of the comparator 7 becomes H level, and the count pulse from the NAND gate 9 goes up and down.
Is supplied to the terminal U for counting up. The up / down counter 11 increments the output count by 0 to 1.

When the output further increases according to the count value, V _L <V _i ″. At this time, the comparator 7
Output changes to L level. There is no change in the output of the comparator 6 and it is an L level output. Therefore, no count pulse is supplied to the up / down counter 11. As long as no pulse is supplied, the output value of the up / down counter 11 holds the count value at the time when it stopped, so that a constant output current continues to be supplied to the inverter 21.

However, the output temperature characteristic of the fluorescent lamp 22 is
It is not stable as shown in FIG. Therefore, the amount of light received by the silicon light receiving element 1 changes with time. When the amount of light rises, the fluorescent lamp 22 emits more light, and when the amount of illumination light rises, the illumination voltage V _i ″ also rises, and V _i ″>
When it reaches V _H , the output of the comparator 6 changes to H level. The NAND gate 8 becomes effective, and the supply of the countdown pulse starts to the up / down counter 11. In the up-down counter 11, when a pulse is input to the count-down terminal D, the count value output up to that point is decremented by one. Therefore, the output current decreases until V _i "<V _H, the illuminance of the fluorescent lamp 22 enters the appropriate range again. Once in the proper range, the up-down counter 11 stops counting. Amount is lowered In the case, when the luminous efficiency of the fluorescent lamp 22 decreases and the amount of illumination light decreases, the illumination voltage V _i ″ decreases. And V _i ”<V _L
Then, the output of the comparator 7 changes to H level. The NAND gate 9 becomes effective, and the supply of pulses for counting up starts to the up / down counter 11. When a pulse is input to the count-up terminal U, the up-down counter 11 increments the count value output up to that point by one. Therefore, the output current rises until V _i ″> V _L, and the illuminance of the fluorescent lamp 22 enters the proper range again, and when it enters the proper range, the up-down counter 11 stops the counting operation.

By the above operation, in the automatic mode, the illuminance of the fluorescent lamp 22 is always kept constant within the set range. This setting range is defined by the high-side reference voltage V _H and the low-side reference voltage V _L. That is, the illuminance at the high-side reference voltage V _H is set as the upper limit value, and the low-side reference voltage V _{L is set.}
The illuminance at is set as the lower limit value. For example, when the appropriate illuminance is 1000 [lx], the illuminance is 1010 [lx].
x], the comparator 6 sets the variable resistor VR ₄ so that the detection signal becomes the H level. Also, the illuminance is 9
When it becomes 90 [lx], the comparator 7 outputs the detection signal H
The variable resistance VR ₅ is set so as to obtain the level. As a result, stable illumination can be obtained within the range of 1000 ± 10 [lx].

When the pulse frequency generated by the oscillator 10 is high, the output is reflected in the fluorescent lamp 22, and the input fed back from the silicon light receiving element 1 is sufficiently faster than the time when the input reaches the comparator section. Reach the upper limit of the count. At that time, control is performed such that the pulse supply is stopped at the maximum count. That is, a gate is provided which detects the output of the up / down counter 11 and outputs a control signal when a predetermined count number (for example, '255') is reached. When the logical product of the count pulse and this control signal is supplied to the NAND gate or the like, the pulse input for counting up to the up / down counter 11 is stopped at a predetermined count number. Similarly, the countdown may be provided with a function of stopping the pulse input for the countdown at a predetermined count value (for example, "0").

FIG. 3 shows the output characteristic of the third embodiment. This characteristic was measured by the illuminance meter M ₃ in the illuminance measurement environment of FIG. This is a plot of the intensity of light received by the silicon light receiving element 1 _-2 directly Figure 3. The alternate long and short dash line indicates the illuminance characteristic (before correction) when the illuminance correction amplifier 20 is switched to the manual mode and the illuminance is adjusted to about 1000 [lx]. The solid line switches the illuminance correction amplifier 20 to the automatic mode and sets the target value to 1000.
It is an illuminance characteristic (after correction) when adjusted to [lx]. As shown in FIG. 3, the illuminance characteristics before correction require time until the target value is reached after the power is turned on, and the illuminance after that is not stable. One of the corrected values starts from the target value, and the illuminance level after that is extremely stable.

According to the embodiment of the present invention, a stable output can be obtained by using a fluorescent lamp whose illuminance is originally not stable. Therefore, if the subject t is provided as shown in FIG. 2, it is possible to irradiate uniform light having no directivity with a constant illuminance like a fluorescent lamp, which is effective in the field of image processing and the like.

The present embodiment is not limited to the above, but can be modified in various ways. For example, although the window range is provided by the operation of the detection unit in the present embodiment, the window may not be formed.
If the window is not formed, it is not necessary to provide two comparators, and the configuration as shown in FIG. 4A is adopted so that the count-up or count-down pulse is output according to the level change of the output level of the comparator. Good. As shown in FIG. 4A, the reference voltage E _t is set so as to reach the target illuminance. The comparator 30 compares the reference voltage E _t with the illuminance voltage V _i and outputs H level and L level. Since the inverter 31 is newly provided, the NAND gates 8 and 9 operate reciprocally. Therefore, when the illuminance is higher than the target illuminance, the countdown is performed, and when the illuminance is lower than the target illuminance, the count is increased, and a constant output is obtained.

Also, a digital process such as a counter is required.
As shown in Fig. 4 (b), the comparator
Output directly controls the current supply driver.
May be. As shown in FIG. 4B, the comparator 32
Is the reference voltage E_tAnd illuminance voltage V _iCompare with. Compare
The output of the data 32 is provided with an integrating circuit 33.
The current supply of the driver circuit is finely adjusted near the reference voltage.
Be done.

The illumination does not have to be a fluorescent lamp, and if the illumination device has a certain degree of correlation between the supplied power and the illuminance, another illumination source (for example, an incandescent lamp) is used. Can be corrected.

[0033]

As described above, according to the present invention, even if a light source with unstable illuminance is used, the illuminance can be stably supplied by the correction operation. Therefore, it is effective as a lighting device in a field requiring uniform illuminance. This illumination can be applied not only to image processing but also to a photography department or a research department that requires measurement under constant illumination.

Further, since the window range in which the illuminance correction operation is not performed is provided, it is possible to minimize unnecessary radiation or the like that occurs as a harmful effect of the correction operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an illuminance correction amplifier according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an illuminance measuring environment of the present invention.

FIG. 3 is an output characteristic diagram of an illuminance correction amplifier.

FIG. 4 is an explanatory diagram showing a modified example of the detection unit of the embodiment.

FIG. 5 is a temperature characteristic diagram of a conventional lighting device.

[Explanation of symbols]

1, 1 _-2 ... Silicon light receiving element 2 ... Input amplifier 3, 14 ... Buffer 4 ... Differential amplifier 5, 13, 15 ... Amplifier 6, 7, 30, 32 ... Comparator 8, 9 ... NAND gate 10 ... Oscillator 11 ... Up-down counter 12 ... D / A converter 20 ... Illuminance correction amplifier 21 ... Inverter 22 ... Fluorescent lamp 23 ... Halogen lamp 24 ... Dark box 31 ... Inverter 33 ... Integration circuit E _O ... Power supply M ₁ ... Illuminance monitor M ₂ ... Output current Monitor M ₃ ... Illuminance meter T ₀ ... Input terminal T ₁ ... Illumination monitor terminal T ₂ ... Output current monitor terminal T ₃ ... Output terminal S ... Shield SW ₁ , SW ₂ ... Switches VR _{1 to} VR ₅ ... Variable resistance R _{1 to} R ₆ ... Resistor Q ... Transistor t ... Subject

Claims (2)

[Claims] 1. A light receiving means (1) for generating an illuminance voltage having a potential difference corresponding to the illuminance of incident light; and a high side reference voltage and a level lower than the high side reference voltage, to which the illuminance voltage is input. Comparing means (6, 7, 8, 9, VR ₄ , VR ₅ ) for comparing both the low side reference voltage and the illuminance voltage and outputting a corresponding control signal, and the comparing means (6, 7, 8) , 9, VR ₄ , VR ₅ ) and a drive means (21) for outputting a drive signal corresponding to the control signal output by the drive means, and a light emission for emitting light with an illuminance corresponding to the drive signal output by the drive means (21). Means (22), the comparison means (6, 7, 8, 9, VR ₄ , VR ₅ )
When the illuminance voltage is lower than the low-side reference voltage, the control signal is changed to increase the illuminance by the drive signal, and when the illuminance voltage is higher than the high-side reference voltage, the drive signal is changed. Changing the control signal in a direction of decreasing the illuminance, and having a non-control range that does not change the control signal when the illuminance voltage is higher than the low-side reference voltage and lower than the high-side reference voltage, Illuminance correction amplifier characterized by. 2. The illuminance correction amplifier according to claim 1, wherein the comparison unit sets a high-side voltage setting unit (VR ₄ ) that sets the high-side reference voltage, and a low-side voltage that sets the low-side reference voltage. Setting means (V
R ₅ ), an oscillator (10) for generating a reference pulse signal, and the reference pulse signal generated by the oscillator (10) are input to compare the illuminance voltage and the high-side reference voltage,
The high side switch means (6, 8) for outputting a high side pulse signal when the illuminance voltage is higher than the high side reference voltage, and the reference pulse signal generated by the oscillator (10) are input to the illuminance voltage And a low-side reference voltage, and outputs a low-side pulse signal when the illuminance voltage is lower than the low-side reference voltage, and a high-side switch means (6, 9). 8) outputs the high-side pulse signal to subtract or add a count signal in the direction of decreasing the illuminance by the drive signal to obtain the low-side pulse signal output by the low-side switch means (7, 9). Based on the drive signal, the up / down counter (11) for adding or subtracting the count signal in the direction to increase the illuminance, and the counter output by the up / down counter (11). Illuminance correction amplifier to be a cement signal and a D / A converting means (12) for outputting a control signal to convert D / A, and characterized.