JPS6285826A - Photodetecting device - Google Patents

Abstract

PURPOSE:To decide and detect only specific light by utilizing the difference in wavelengths spectrum distribution between background light and detection light. CONSTITUTION:A short-wavelength photodetector 2 and a long-wavelength photodetector 3 detect incident light 1 and convert it into electric signals. Their outputs are inputted to a differential amplifier 4. The differential amplifier 4 amplifies the difference between both signals. Its output is therefore a minus- side output when the input signal at the inverted input side is larger and a plus-side output when smaller, so that they can be discriminated clearly. For the purpose, this output is inputted to a comparator 5 and compared with a proper slice level, thus obtaining a decision output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light detection device whose purpose is to detect only specific light in an environment with a lot of background light.

[Conventional technology]

Traditionally, in environments with a lot of background light, especially 'fc
.

[Problem that the invention seeks to solve]

For example, this type of detection may be difficult if the sensor is to be sensitive only to electric lamp light and not to σ sensitivity to sunlight. It is impossible to distinguish black ink based on differences in light intensity.

There is a method of selecting only specific wavelengths and comparing them, but when it comes to wavelengths that are included only in sunlight and electric light, it is difficult to select a detector.

[Failure to solve the problem]

In order to solve these problems, the present invention utilizes the difference in wavelength spectral distribution between the background light and the detection light for discrimination. That is, the distribution of the emission spectrum differs depending on the color temperature of the light source. A light source with a high color temperature such as sunlight has a spectral intensity in a short wavelength range that is stronger than that in a long wavelength range. On the contrary, for light sources with low color temperature such as electric lamps, the spectral intensity in the long wavelength range is higher than that in the short wavelength range. become stronger than

Therefore, by using a photodetector sensitive to short wavelength range and a photodetector sensitive to long wavelength range, each output differential
It is possible to manually distinguish the differential output level by adjusting the VC.

[Yi h1! ! Leli Next, the present invention will be explained with reference to the drawings.

Figure 41 is a system diagram showing an embodiment of the original detection device ft (7) according to the invention, in which the short wavelength photodetector 2 and the long wavelength photodetector 3 detect all of the incident light 1. 1ki 1gi issue fCf
Chivalry. Manually connect the differential input terminals of each output fully differential amplifier. The difference between both signals is applied to the differential amplifier by N width. Therefore, if the input value on the inverting input side is large, the output becomes the @- side output, and if it is small, it becomes the + side output, and can be clearly distinguished. This output is manually input to the comparator 5 and compared at an appropriate slice level to obtain a discrimination output.

Also, by changing the area of each detector, an attenuation filter is inserted f1
Incident light*'! : By adjusting, the discrimination level of the energy ratio between the short wavelength side and the long wavelength side can be freely changed.

As for the detector, you can use two types of detectors with different wavelength sensitivities, or you can use a combination of a short wavelength transmission filter 21 in front of the detector 22 and a long wavelength filter in front of the detector 32 as shown in Figure 2. A combination of side transmission filters 31 may also be used.

〔Effect of the invention〕

As described above, by discriminating all light sources with different color temperatures according to the present invention, it is possible to provide all light detection devices without malfunction.

[Brief explanation of drawings]

The first factor is a system block diagram of the present invention, and FIG. 2 is a diagram 1j showing details of the detector.

Claims (1)

[Claims] A short wavelength photodetector, a long wavelength photodetector, a differential amplifier that outputs a signal corresponding to the difference in the output of each of these detectors, and detects only specific light based on the output level of this differential amplifier. What is claimed is: 1. A light detection device comprising: a comparator for detecting