JPH02228895A - Automatic white balance module - Google Patents

Abstract

PURPOSE:To improve the directivity of a color temperature characteristic and a low illuminance characteristic by arranging a diffusion board on the incident surface side of an infrared cut filter and arranging a condenser lens between a photo-detector and the infrared cut filter. CONSTITUTION:Since a diffusion board 16 is arranged in an incident surface 15 side (front surface) of an infrared out filter 14, incident light is diffused by the diffusion board 16 and the of the infrared cut filter is not made uniform and a change in the output of a photo detecting element 10 according to the incident angle of the incident light is reduced and the directivity of the color temperature characteristic is eliminated. Since a condenser lens 17 is arranged between a photodetector 11 and the infrared cut filter 14, the transmissive light of the infrared cut filter 14 is condensed and can be made incident to the photo-detecting element 10 in the photodetector 11. Thus, an output can be enlarged without enlarging the photo-detecting area of the photo-detecting element 10 and the low illuminance characteristic is improved. Then, the shape of a module itself is made small and cost can be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to the configuration of an auto white balance module used in VTR cameras, electronic still cameras, and the like.

<Prior art> A conventional auto white balance module consists of a light receiving device that has multiple light receiving elements with different spectral sensitivities, and an infrared cut filter that is placed on the light receiving surface side of the light receiving device and blocks incident light in the infrared 1 range. It is configured. Of the light that has entered the module, the infrared light is blocked by an infrared cut filter, and the light receiving element of the light receiving device receives the incident light in the visible light range to correct white balance.

Here, the purpose of white balance will be explained.

The human sense of color is such that when we see something white under any light source, we perceive it as white. for example,
A "white object" viewed under a light source with a high color temperature (under a blue light source) is equally white as a "white object" viewed under a light source with a low color temperature (under a red light source).

I feel it as something ugly. This is because humans and the naked eye correct changes in the spectral characteristics of the light source based on past sensations such as "memory color."

On the other hand, VTR cameras, electronic still cameras, etc.
When viewing an object with an OD, image pickup tube, etc., a white object may not appear white depending on the light source. for example,
When viewed under a light source with a high color temperature, "white objects" appear blue,
White objects may appear red when viewed under a light source with a low color temperature. Therefore, in order to reproduce white as seen with the human eye, it is necessary to electrically correct changes in the spectral characteristics of the light source.

In general, an auto white balance correction circuit that automatically performs such white balance correction uses a light receiving system that is composed of a plurality of light receiving elements having sensitivities corresponding to different colors through an optical system 1, as shown in FIG. 2, for example. The device (auto white balance sensor (AWB sensor)) 2 detects the color temperature of the light source, and the signal processing circuit 3 outputs an R/G signal corresponding to the ratio of green to red and a ratio of green to blue, for example. Equipped with an auto white balance sensor circuit that obtains corresponding G/B signals, R, G, and H obtained from the image pickup tube 4 via the color separation circuit 5 based on the R/G signal and the G/B signal are provided.
Of each signal, the R signal and the B signal are processed by signal processing circuits 6 and 8.
It is now possible to perform color correction using the controls.

Note that the outputs IR/IC and IG/IB of the light receiving device 2 have characteristics as shown in FIG.

The measurement conditions at this time were that the power supply voltage was 5V and the outside temperature was 25V.
degree, the resistance value is 100Ω, and the output voltage is ■. (B-
G)-V. (GR) It was measured with the voltage adjusted to -1.8V.

〉 Problems to be Solved by the Invention 〉 However, as shown in Figure 4, the light that enters the autopowder wide balance module includes light that is incident at right angles (perpendicularly) (
There is also light (vertically incident light) X and obliquely incident light (obliquely incident light) Y.

Therefore, in the conventional automatic wide balance module, these incident lights X and Y directly enter the infrared cut filter 9, so the infrared cut filter transmission distance Q1 when the incident lights are perpendicular to the infrared cut filter when they are incident obliquely is The filter transmission distance gd differs by f2+<12t&. This changes the spectral characteristics of the light receiving element and changes the output of the light receiving element.

Specifically, in a light receiving element sensitive to red, the fifth
As shown in the figure, the red output IRy for the oblique incident light Y that has passed through the transmission distance Q is smaller than the red output IRx for the normal incidence angle X that has passed through the transmission pressure M(1, The output IR/IG shown in the figure is 7, which changes depending on the angle of incidence.

Note that the light receiving element sensitive to red is p
It is a photodiode in which a layer and an n layer are joined (pn junction), and a red filter 1 is placed on its light receiving surface as shown in FIG.
0b is installed. The spectral characteristics of this light receiving element are obtained by combining the output IR of the light receiving element 10a without the infrared cut filter 9 and the spectral transmittance IRt of the infrared cut filter 9, as shown in FIG. It is.

In addition, the illuminance characteristics of the auto white balance module are determined by the dark current and the output of the light receiving element, so the output of the light receiving element is sufficiently large compared to the dark current value, so that the dark current can be ignored. There is a need. To achieve such a state, it is necessary to increase the area of the light-receiving element, but increasing the area of the light-receiving element increases the cost and increases the size of the module itself.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide an auto white balance module with excellent color temperature directionality and low illuminance characteristics.

<Means for Solving the Problems> The means for solving the problems according to the present invention is that a diffusion plate and a condensing lens are arranged in front of a light receiving element, that is, the first
As shown in the figure, a plurality of light receiving elements 10 having mutually different spectral sensitivities
and a light receiving surface 12 of the light receiving device 11.
The infrared cut filter 1 includes an infrared cut filter 14 disposed on the side and blocks incident light 13 in the infrared region.
A diffusion plate 16 for diffusing incident light 13 from the outside is disposed on the incident surface 15 side of 4, and a condensing lens 1 for condensing the incident light 13 between the light receiving device 11 and the infrared cut filter 14.
7 is placed on it.

Effect> In the above problem solving means, the light 13 entering the auto white balance module is diffused by the diffusion plate and enters the infrared cut filter 14.

Of this incident light 13, the light in the infrared region is blocked by the infrared cut filter 14, and the light only in the visible region is condensed by the condenser lens 17 and enters the light receiving element 1O in the light receiving device 11. Next, the color temperature of the light source is detected by the light receiving element IO in the light receiving device li, and this signal is controlled by an auto white balance correction circuit to correct the white balance.

At this time, since the diffuser plate 16 is arranged on the incident surface 15 side (front surface) of the infrared cut filter 14, the vertically incident light is diffused by the diffuser plate 16, which is different from the conventional method in which the vertically incident light directly enters the infrared cut filter. Like a module, the transmission distance of the infrared cut filter is not uniform, and light that is longer than the transmission distance of the vertically incident light that directly enters the infrared cut filter also enters the infrared cut filter 14.

In addition, the obliquely incident light is also diffused by the diffuser plate 16 in the same way as the vertically incident light, and the transmission distance of the infrared cut filter is not uniform, so that the infrared rays are also cut for light that is shorter than the transmission distance of the obliquely incident light that directly enters the infrared cut filter. Filter 14
It will be incident on .

Therefore, the change in the output of the light receiving element IO due to the angle of incidence of the incident light is reduced, and the directivity of the color temperature characteristic is eliminated.

Furthermore, since the condensing lens 17 is arranged between the light receiving device 11 and the infrared cut filter i4, that is, in front of the light receiving device 11, the condensing lens 17 can be used as a condensing lens! 7 makes it possible to condense the light transmitted through the infrared cut filter 14 and make it enter the light receiving element 10 in the light receiving device 11.

As a result, the output of the light-receiving element 11 can be increased without increasing the light-receiving area of the light-receiving element 11, the low-illuminance characteristics are improved, the shape of the module itself is reduced, and the cost is reduced.

<Example> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an auto white balance module showing one embodiment of the present invention.

As shown in FIG. 1, the auto white balance module of the present invention includes a light receiving device (auto white balance sensor) 11 having a plurality of light receiving elements IO having mutually different spectral sensitivities.
And the light receiving device 1! The infrared cut filter 14 is arranged on the light receiving surface 12 side of the infrared cut filter 14 and blocks the incident light 13 in the infrared region. Incident light from the outside on the incident surface 15 side of 4! A diffuser plate that diffuses 3! 6 is arranged, and the light receiving device! A condensing lens 17 that condenses the incident light 13 is arranged between the infrared cut filter 14 and the infrared cut filter 14.

The light receiving element IO is a pn junction photodiode, and includes a red light receiving element sensitive to red light, a green light receiving element sensitive to green light, and a blue light receiving element sensitive to blue light. The light receiving device 1 is assembled with the elements.
Built in 1.

The light receiving device 11 is connected to an auto white balance correction circuit (not shown), and the module main body 17° is connected to an auto white balance correction circuit (not shown).
A light receiving device mounting hole 18 formed in a stepped manner at an appropriate position.
It is removably attached to the.

A holder 19 for holding and fixing optical system components, that is, the infrared cut filter 14, the diffusion plate 16, and the condensing lens 17, is arranged above the main body 17. The holder 19 is formed in a cylindrical shape and has an optical system component mounting hole 20 in which an infrared cut filter 14, a diffuser plate 16, and a condensing lens 17 are removably mounted at positions corresponding to the mounting hole 18. The mounting hole 20 has an upper stepped portion 21. The middle stepped portion 22 and the lower stepped portion 23 form a stepped shape, and the upper stepped portion 21 is provided with a diffusion plate 16.
is placed, an infrared cut filter 14 is placed on the middle stepped portion 22, and a condenser lens 17 is placed on the lower stepped portion 23.

The diffusion plate I6 is formed into a plate shape by adding an ultraviolet absorber to glass-filled polycarbonate (G-3120 manufactured by Teijin Chemicals Ltd.).

The condensing lens 17 is a spherical lens with a curvature of 4 mm or 5 mm, and is fitted and held in the lens frame 24.

Note that the infrared cut filter and auto white balance correction circuit are configured similarly to those described in the related art.

In the above configuration, the light 13 entering the auto white balance module is diffused by the diffusion plate and enters the infrared cut filter 14. Of this incident light 13, light in the infrared region is blocked by an infrared cut filter 14, and only light in the visible region is condensed by a condenser lens 17 and enters the light receiving element 10 in the light receiving device il.

Next, the color temperature of the light source is detected from the light receiving element 101 in the light receiving device 11, and this signal is controlled by an auto white balance correction circuit to correct the white balance.

At this time, since the diffuser plate 16 is arranged on the incident surface 15 side (front side) of the infrared cut filter 14, the vertically incident light is diffused by the diffuser plate 16, and the infrared cut filter transmission distance is changed as shown in FIG. In the end, only gI disappears. That is, light whose transmission distance is longer than Ql also enters the infrared cut filter 14.

Further, the obliquely incident light is also diffused by the diffuser plate 16 in the same way as the vertically incident light, and the transmission distance of the infrared cut filter is no longer only Q. That is, light having a transmission distance shorter than Q also enters the infrared cut filter 14.

Therefore, the change in the output of the light receiving element IO due to the angle of incidence of the incident light is reduced, and the directivity of the color temperature characteristic is eliminated.

Furthermore, since the condensing lens 17 is arranged between the light receiving device 11 and the infrared cut filter 14, that is, in front of the light receiving device 11, the light transmitted through the infrared cut filter 14 is condensed by the condensing lens 17. It becomes possible to make the light incident on the light receiving element 1O in the light receiving device 2.

As a result, the output of the light-receiving element 11 can be increased without increasing the light-receiving area of the light-receiving element 11, the low-illuminance characteristics are improved, the shape of the module itself is reduced, and the cost is reduced.

By arranging a diffuser plate and a condensing lens in front of the light receiving element, the output of the light receiving element is approximately 2.6 times higher than that without the diffuser plate and condensing lens. The rR/rGO value fluctuated about three times less than when no diffuser plate was used.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in the above embodiment, a light receiving device equipped with a light receiving element sensitive to red light, green light, and blue light is used; You may use the light receiving device provided with the light receiving element which has.

Further, the present invention may be applied to a light receiving device having two or four or more types of light receiving elements instead of a light receiving device having three types of light receiving elements.

<Effects of the Invention> As is clear from the above description, according to the present invention, a light receiving device having a plurality of light receiving elements having mutually different spectral sensitivities;
In an auto white balance module that includes an infrared cut filter that is placed on the light receiving surface side of the light receiving device and blocks incident light in the infrared region, the diffusion plate is placed on the incident surface side (front) of the infrared cut filter. , the vertically incident light is diffused by the diffuser plate, the transmission distance of the infrared cut filter is not uniform, and light that is longer than the transmission distance of the vertically incident light that directly enters the infrared cut filter also enters the infrared cut filter. . In addition, obliquely incident light is also diffused by the diffuser plate in the same way as vertically incident light, and the transmission distance of the infrared cut filter is not uniform. It will be incident on .

Therefore, the change in the output of the light receiving element 10 due to the angle of incidence of the incident light is reduced, and the directivity of the color temperature characteristic is eliminated.

In addition, since the condensing lens is placed between the light receiving device and the infrared cut filter, that is, in front of the light receiving device,
The condensing lens makes it possible to condense the light transmitted through the infrared cut filter and make it enter the light receiving element in the light receiving device.

This makes it possible to increase the output without increasing the light-receiving area of the light-receiving element, and improves low-light characteristics.
The size of the module itself becomes smaller and the cost becomes cheaper.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an auto white balance module showing an embodiment of the present invention, Fig. 2 is a diagram showing an auto white balance correction circuit of a conventional auto white balance module, and Fig. 3 is a diagram showing the incidence of the output voltage. Figure 4 is a diagram showing the light color temperature characteristics, Figure 4 is a diagram showing the state in which incident light passes through an infrared cut filter, Figure 5 is a diagram showing the spectral characteristics of the light receiving element, and Figure 6 is the same as the light receiving element. FIG. 7 is a diagram showing a state in which the spectral characteristics of the light receiving element are obtained. 10; Light receiving element, Ii; Light receiving device, 13; Incident light, 14
;Infrared cut filter, 16: Diffusion plate,! 7; Condensing lens. Attorney-at-Law Sharp Co., Ltd. Tsunehisa Nakamura

Claims (1)

[Claims] It is equipped with a light receiving device having a plurality of light receiving elements having mutually different spectral sensitivities, and an infrared cut filter arranged on the light receiving surface side of the light receiving device to block incident light in the infrared region. An auto white balance module characterized in that a diffusion plate is disposed to diffuse incident light from the light receiving device, and a condenser lens for condensing the incident light is disposed between the light receiving device and the infrared cut filter.