JP2006237380A - Optical sensor circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sensor circuit device where the life of a battery as a power source can be extended by reducing current consumption. <P>SOLUTION: The device comprises a photoelectric conversion means for outputting a current of a value according to the illumination of received light, and a logarithm conversion means which is supplied with output current of the photoelectric conversion means and carries out logarithm conversion of it to output. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical sensor circuit device, and more particularly to an optical sensor circuit device that amplifies and outputs an output signal of a photodiode.

  In general, since an output signal of a photodiode is a weak current, it is amplified by an amplifier circuit and output.

  FIG. 4 shows a block diagram of an example of a conventional optical sensor circuit device. In the figure, a photodiode 10 receives light and outputs a current having a value corresponding to the illuminance of the received light. The output current of the photodiode 10 is amplified by the linear amplifier 12 and output from the terminal 14.

  FIG. 5 shows the illuminance / output current characteristics of a conventional optical sensor circuit device. In FIG. 5, a solid line I indicates the illuminance / output current characteristics of the photodiode 10 alone, and a solid line II indicates the illuminance / output current characteristics of the conventional photosensor circuit device. As is apparent from this figure, the output current of the conventional photosensor circuit device is proportional to the illuminance of light.

  In addition, although the well-known literature was investigated about the technique regarding the illumination intensity and output current characteristic of a photosensor circuit device, the well-known literature corresponding to this was not discovered.

  The output current of the optical sensor circuit device shown in FIG. 4 is used for an application that automatically adjusts the luminance of the backlight of the liquid crystal display device. That is, the illuminance in the liquid crystal display device is detected by the optical sensor circuit device, and the luminance of the backlight is determined according to the magnitude of the output current.

  In the conventional optical sensor circuit device, for example, when an output current of 200 μA is obtained at an illuminance of 100 lux, the current output is 10 times 2 mA, 1000 lux, and 100 times 20 mA, 10000 lux. In other words, in an environment of 10 to 10000 lux, the output current range is 2 μA to 20 mA, and since the output current is large when the illuminance is large, the current consumption of the photosensor circuit device is large. There was a problem that the lifespan of the product was shortened.

  In addition, when the output current at a large illuminance is designed to be small, there is a problem that the output current at a small illuminance becomes weak and easily affected by noise.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an optical sensor circuit device that can significantly reduce the output current when the illuminance is large as compared with the conventional art.

The invention according to claim 1 is a photoelectric conversion means for outputting a current having a value corresponding to the illuminance of received light;
By having logarithmic conversion means that is supplied with the output current of the photoelectric conversion means and performs logarithmic conversion to output,
The output current when the illuminance is large can be greatly reduced as compared with the conventional case.

  According to the present invention, current consumption can be reduced and the life of a battery as a power source can be extended.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a block diagram of an embodiment of the optical sensor circuit device of the present invention. In the figure, a photodiode 20 receives light and outputs a current having a value corresponding to the illuminance of the received light. The output current of the photodiode 20 is supplied to the logarithmic amplifier 22. The logarithmic amplifier 22 performs logarithmic conversion of the input current and outputs it from the terminal 24.

  FIG. 2 shows a circuit diagram of a main part of the logarithmic amplifier. In the figure, the output current of the photodiode 20 is supplied to the terminal 30. Terminal 30 is connected to the inverting input terminal of operational amplifier 31. The non-inverting input terminal of the operational amplifier 31 is grounded, and the output terminal of the operational amplifier 31 is connected to the terminal 32 via the resistor R1. The inverting input terminal and the output terminal of the operational amplifier 31 are connected by a capacitor Cf. Further, the collector of an npn transistor Tr1 is connected to the terminal 30, the base of the transistor Tr1 is grounded, and the emitter is connected to the terminal 32.

  The output voltage Vo of the terminal 32 with respect to the input current Is of the terminal 30 is expressed by equation (1).

Vo = −kT / q (lnIs−lnIe) (1)
Here, k is a Boltzmann constant, q is an electron charge, T is an absolute temperature, ln is a natural logarithm, and Ie is an emitter saturation current of the transistor Tr1.

The signal logarithmically converted by the above equation (1) is supplied from the terminal 32 to the next-stage amplifier, and is amplified by the next-stage amplifier at a predetermined amplification factor (for example, 4.334294 × 10 ⁻⁵ ), And output as an output signal of the logarithmic amplifier 22.

  FIG. 3 shows the illuminance / output current characteristics of the optical sensor circuit device of the present invention. For example, when designed to obtain an output current of 200 μA at an illuminance of 100 lux, a current output of 400 μA, which is twice as large as 10000 lux, can be obtained as 1.5 times 300 μA. That is, in the environment of 10 to 10000 lux, the output current range is 100 μA to 400 μA.

  As described above, the output current when the illuminance is large can be significantly reduced as compared with the conventional case, and the current consumption of the optical sensor circuit device can be greatly reduced. For this reason, when the power source is a battery, it is possible to extend the life of the battery.

It is a block diagram of one embodiment of a photosensor circuit device of the present invention. It is a circuit diagram of the principal part of a logarithmic amplifier. It is an illumination intensity-output current characteristic view of the optical sensor circuit device of the present invention. It is a block diagram of an example of the conventional optical sensor circuit device. It is an illumination intensity-output current characteristic view of the conventional optical sensor circuit device.

Explanation of symbols

20 photodiode 22 logarithmic amplifier 31 operational amplifier Cf capacitor R1 resistance Tr1 npn transistor

Claims (3)

Photoelectric conversion means for outputting a current having a value corresponding to the illuminance of the received light;
An optical sensor circuit device comprising logarithmic conversion means that is supplied with an output current of the photoelectric conversion means and performs logarithmic conversion to output. The optical sensor circuit device according to claim 1,
The photoelectric sensor circuit device is characterized in that the photoelectric conversion means is a photodiode. The optical sensor circuit device according to claim 2,
The optical sensor circuit device, wherein the logarithmic conversion means is a logarithmic amplifier.

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