JPH06244396A - Testing of image sensor - Google Patents

Abstract

PURPOSE:To test variation in photodetection sensitivity of a plurality of photosensors accurately by applying a flux of test light of uniform optical intensity distribution to an image sensor. CONSTITUTION:Test light Lt to be applied to an image sensor 10 is generated by a light source 30 which has an incandescent lamp 31 and a reflecting board 32 and a flux of the light is applied to a compound-eye aggregate lens body 40 which is made by arranging small lenses 41 flatly through an optical fiber 34 or a rod photoconductor 42 and then the light is converged at a focus of each of the small lenses 41. By this, the test light Lt is converted into a flux of nearly uniform distribution and then is allowed to enter a photo diffusion box 50 through an incident window 53. Being reflected by a diffusive inner face of the box, the test light Lt confined inside the box is emitted as a diffusive light flux Ld through an emission window 54 made of lightdiffusive window material 55 such as opal glass and then is applied to the image sensor 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing variations in the light detection sensitivities of a plurality of photosensors in order to confirm the image detection accuracy of an image sensor.

[0002]

2. Description of the Related Art In an image sensor such as a CCD device or a photodiode array, a large number of photosensors can be integrated in a small chip by utilizing integrated circuit technology. The demand for heightening is becoming stronger. For example, an image sensor for an auto-focus camera is required to have high accuracy capable of converting the light intensity received by each optical sensor into 4-bit or more digital data. In order to meet such a demand, of course, the photodetection characteristics of the photosensors in the image sensor must be evenly arranged according to the required level of image detection accuracy. It is necessary to test, and for this test, it is necessary to make a sufficiently uniform luminous flux enter the image sensor.

FIG. 2 shows an example of a conventional method suitable for applying the uniform luminous flux of test light to an image sensor. As shown in the figure, the test light Lt is generated by, for example, a pair of light sources 30, reflected by a diffusion plate 60 to be converted into a diffusive light beam, and then incident on the image sensor 10. An incandescent lamp 31 such as a halogen bulb that emits light with a wide wavelength distribution suitable for the test is used as the light source 30, and is combined with the reflector 32 so as to spread the luminous flux given to the diffuser 60 as much as possible. A diffuser plate 60 coated with a matte white paint is used. In this conventional method, the distance between the light source 30 and the diffusing plate 60 and the distance between the diffusing plate 60 and the image sensor 10 are set as large as possible, and the diffusing or scattering property of the diffusing plate 60 with respect to light is increased to obtain a substantially uniform value suitable for the test. It is possible to provide the image sensor 10 with a diffusive light flux of the test light Lt having various intensity distributions.

In the conventional example shown in FIG. 3, a diffusion box 50 is used instead of the diffusion plate 60 shown in FIG. The light source 30 is an incandescent lamp 31 and a reflector 32 housed in a case 33, and the diffusion box 50 is a case.
An entrance window 53 that receives a light flux from the light source 30 by applying a diffusion coating 52 to the inner surface of 51 and a window 54 that exits the light flux of the test light Lt are provided in the image sensor 10, and the exit window 54 is made of a light-diffusing milky white glass or the like. A certain window material 55 is attached. In this conventional method, the test light Lt from the light source 30 is repeatedly reflected on the inner surface of the diffusion box 60 to form a diffusive light beam, and the diffusivity is further increased by the window material 55 to test the image sensor 10 for a uniform light intensity distribution. Light Lt can be given. A measuring device is connected to the image sensor 10 which receives the test light Lt according to the conventional method shown in FIGS. 2 and 3, and the photodetection signal value of each photosensor is measured to test the variation in the detection sensitivity.

[0005]

However, recently, the demand for improving the image detection accuracy of the image sensor has been increasing more and more, and in response to this, the light intensity received by each optical sensor of the image sensor is, for example, 8-bit accuracy. In order to increase it to the extent that it can be converted into digital data, it is necessary to suppress the variation in the detection sensitivity of the optical sensor to 0.4% or less. It is necessary to equalize within a smaller error range of, for example, 0.1% or less. However, the conventional method described with reference to FIGS. 2 and 3 has a problem that it is very difficult to make the test light uniform within an error range of 1% or less.

That is, according to the conventional method of FIG. 2, it is difficult to obtain a diffuser plate 60 having good light diffusivity, and the intensity distribution of the test light Lt received by the image sensor 10 is easily changed depending on the position where the light source 30 is placed. As described above, it is difficult to make the intensity distribution uniform even if the positions of the light sources 30 are changed in various ways. Further, if the diffusion plate 60 is separated from the image sensor 10 or the light source 30 by a distance of 3 to several meters, the problem can be alleviated considerably, but the utilization efficiency of the test light Lt is remarkably reduced and the test under high light intensity becomes difficult. , The test equipment including the light projection system becomes very large. Also, in the conventional method of FIG. 3, the projection system can be much smaller, but the test light of the diffusion box 50
It is difficult to improve the performance of converting Lt into a diffusive light flux, and when the incandescent lamp 31 is used as the light source 30 as described above, when the image sensor 10 is tested at a low light intensity contrary to FIG. There is a problem that the uniformity of the test light Lt is particularly likely to deteriorate.

Under such circumstances, the object of the present invention is to provide a light intensity distribution of test light so that even if the image detection accuracy of the image sensor is increased, the variation in the light detection sensitivity of the optical sensor can be tested with high accuracy. To make it uniform.

[0008]

SUMMARY OF THE INVENTION In the present invention, the above object is to arrange the test light generated by the light source in a plane form in order to test the variation in the light detection sensitivity of the plurality of photosensors of the image sensor. Given to the assembled lens body,
A light flux of test light is applied from the collective lens body to a light diffusing box through an entrance window, and the test light emitted from the light diffusing exit window is projected onto an image sensor to test the light detection sensitivity of each light sensor. To achieve.

It is advantageous to downsize the light projecting device by giving the test light generated by the light source to the collective lens body through the optical fiber. Furthermore, the test light from this optical fiber is used. It is advantageous to provide the collective lens body via the light guide in order to enhance the uniformity of the light intensity distribution of the test light provided to the image sensor. Further, in order to improve the uniformity, it is advantageous to make the focal point position of the small lens of the lens assembly substantially coincide with the entrance window of the light diffusion box. It is preferable to attach a light diffusing window material such as milky white glass to the light diffusing exit window of the diffusion box as in the conventional case. When the test light given to the image sensor has a wavelength distribution in a desired range, it is most rational to attach a wavelength selective filter to the entrance window of the diffusion box.

[0010]

In the method of the present invention, the use of the diffusion box is the same as in the conventional example of FIG. 3, but the test light is incident on the entrance window through the collective lens body in which the small lenses described in the above construction are arranged in a plane. Solve the problem by giving. This collective lens body divides the test light beam received by each small lens and condenses it on its focal point or focal plane, but the condensing point or small condensing surface is of course distributed according to the arrangement of the small lenses. Therefore, it serves to disperse the luminous flux of the test light almost uniformly within the area of the entrance window of the diffusion box. Therefore, in the method of the present invention, the test light is provided in the area of the entrance window of the diffusion box with a more uniform distribution than in the conventional case, and the test light is emitted from the light-diffusing exit window while sufficiently exhibiting the performance of diffusing the light in the diffusion box. It is possible to take out the luminous flux of and to project it on the image sensor with a more uniform light intensity distribution than in the conventional method.

[0011]

Embodiments of the present invention will be described below with reference to FIG. The image sensor 10 as the test object shown in the lower left part of the figure is a semiconductor chip 11 in which a plurality of photosensors such as photodiodes are integrated, mounted on a lead frame 12 and housed in a transparent package 13, In the test, as shown in the drawing, the lead 14 is inserted into the wiring board 15 and mounted, and then connected to the measuring device 20 via the connector 16 and the connecting wire 47. Light source for test light Lt shown in the lower right of the figure
Reference numeral 30 is a case in which a daylight-colored incandescent lamp 31 such as a halogen bulb and a reflector 32 are housed in a case 33 as in the conventional example shown in FIG.

In principle, the test light Lt emitted from the light source 30 may be directly applied to the collective lens body 40 shown in the central portion of the drawing, but in the illustrated embodiment, it is passed through the optical fiber 34 and the optical conductor 42. The test light Lt is transmitted to the condenser lens body 40. Optical fiber
34 is an ordinary one in which a large number of glass fibers are bundled and covered with a sheath 35, and one end of the one attached to the case 33 of the light source 30 by the connecting tool 36 receives the test light Lt. Collective lens body 40
Is a small glass lens that is distributed in the lower surface of a circular glass block to form a large number of small hemispherical projections.
41, which is housed in a case 43 together with a light guide 42 which is, for example, rod-shaped optical glass. The case 43 has its lower end portion screwed into the case 51 of the light diffusing box 50 while adjusting the mounting position, and then fixed with the lock nut 44, and the other end of the optical fiber 34 is connected to the upper end portion thereof via the connector 37. It is attached.

The diffusing box 50 may be the same as that used in the conventional method shown in FIG. 3, and the case 51 is provided with a white, preferably uneven diffusing coating 52 on the inner surface thereof so that the test light Lt received from the entrance window 53 can be received. The test light Lt may be taken out through the window material 55 such as a diffusive milky white glass attached to the exit window 54 while being reflected while being reflected on the inner surface, but in this embodiment, the test light Lt is suitable for the test of the image sensor 10. For example, a so-called N having a wavelength selectivity in order to have a wavelength distribution
An optical filter 56, which is a D filter, is attached to the entrance window 53, and the test light Lt is taken in through it. It is preferable that the optical filters 56 having different light transmittances can be replaced so that the image sensor 10 can be tested by switching the intensity level of the test light Lt.

In the light projecting device of this embodiment constructed as described above, the test light Lt from the light source 30 passes through the optical fiber 34 and is in the form of a light beam having a certain divergence angle.
Enter 40. The light guide 40 transmits the obliquely traveling component in the light flux of the test light Lt while totally reflecting it on the peripheral surface thereof, and gives the light flux having a uniform light intensity distribution to the collective lens body 40. The collective lens body 40 concentrates this light flux on the focal points or focal planes distributed according to the arrangement for each small lens 41 to uniformly disperse the test light Lt within the light flux area and then the diffusion box 50.
Give to. The diffusion box 50 uses this as an optical filter 56 for the entrance window 53.
The test light Lt, which is received via the light source, is converted into a wavelength distribution suitable for the test by the inner coating 52 and is confined inside while being emitted as a diffusive light flux Ld from the emission window 54. The light is further strengthened by the semi-transparent window material 55 and then projected onto the image sensor 10 as a light flux of the test light Lt.

As described above, in the present invention, the light flux of the test light Lt generated by the light source 30 is converted into a light flux having a uniform light intensity distribution by the collective lens body 40 in which the small lenses 41 are arranged in a dragonfly compound eye shape. Since it is given to the diffusion box 50, the light intensity distribution of the diffusive light flux of the test light Lt given to the image sensor 10 can be made more uniform than before. According to the experimental results of the embodiment of FIG. 1, the brightness converted into the brightness of the test light Lt given to the image sensor 10 is a so-called luminescence value LV of 6, or 4.5 Cd /
When it is cm ² , the variation of the light intensity received by many photosensors is within 4 × 10 ^-3 Cd / cm ² , and it can be suppressed to 0.1% or less when the ratio is set. This is 1 in case of the conventional method
It can be seen that the uniformity of the test light Lt is improved by about one digit according to the present invention as compared with the fluctuation of about%.

Further, in this experimental result, when the collective lens body 40 is adjusted so that the focal point of the small lens 41 coincides with the position of the entrance window 53 of the diffusion box 50, that is, the upper surface of the optical filter 56 in the example of FIG. The test light Lt has the best uniformity. When testing the image sensor 10 that receives the test light Lt from the light projecting device thus adjusted, the maximum value, the minimum value, and the average value of the light detection signal values of the respective optical sensors are measured by the measuring device 20 of FIG. By doing so, it is possible to determine the quality of the image sensor 10 by measuring the variation in the photodetection sensitivity of the plurality of photosensors. Further, the image sensor 10 can be tested by switching the intensity level of the test light Lt by replacing the optical filter 56.

[0017]

As described above, according to the method of the present invention, when testing the variation in the photodetection sensitivity of the plurality of photosensors of the image sensor, the light flux of the test light generated from the light source is made flat on the small lens. The test light extracted from the light diffusing exit window of the light diffusing box is applied to the image sensor after it is applied to the arrayed collective lens body to convert it into a light flux with a uniform light intensity distribution, and then applied to the light diffusing box through its entrance window. By projecting the light to test the photodetection sensitivity of the photosensor, the variation in the intensity distribution of the test light received by the photosensor of the image sensor is reduced from about 1% in the past to 0.1% to reduce the photodetection sensitivity of the photosensor. Can be tested more accurately than before. INDUSTRIAL APPLICABILITY The method of the present invention is suitable for testing a high-precision image sensor capable of converting the light intensity received by the optical sensor into digital data having an accuracy of 4 bits or more. It makes it possible to start the test.

[Brief description of drawings]

FIG. 1 is a cross-sectional view including an image sensor and a light projecting device showing an embodiment of an image sensor testing method according to the present invention.

FIG. 2 is a layout diagram of an image sensor, a light source, and a diffusion plate showing an example of a conventional image sensor test method.

FIG. 3 is a sectional view of a light source and a diffusion box showing another example of a conventional test method.

[Explanation of symbols]

 10 Image sensor 20 Measuring device 30 Light source 34 Optical fiber for transmitting test light 40 Collective lens body 41 Small lens 42 Light conductor 50 Light diffusing box 53 Light diffusing box entrance window 54 Light diffusing box exit window 55 Exit window material 56 Optical filter Ld Diffuse luminous flux Lt Test light or its luminous flux

Claims (3)

[Claims] 1. A method for testing a variation in light detection sensitivity of a plurality of optical sensors of an image sensor, wherein test light generated by a light source is applied to a collective lens body in which small lenses are arranged in a plane, and the collective lens is provided. The light flux of the test light from the body was given to the light diffusing box from the entrance window, and the test light taken out from the light diffusing exit window was projected to the image sensor to test the light detection sensitivity of the light sensor. Image sensor testing method characterized by. 2. A method according to claim 1, wherein the test light generated by the light source is applied to the collective lens body through an optical fiber. 3. A method for testing an image sensor according to claim 1, wherein the focal point of each small lens of the lens assembly is made to substantially coincide with the entrance window of the light diffusion box.