Radiant energy – Photocells; circuits and apparatus – Housings
Reexamination Certificate
2002-02-06
2004-12-14
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Housings
C250S216000
Reexamination Certificate
active
06831268
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to an optical radiation sensor device, and more particularly to a sensor device incorporating a photosensor.
Light sensors are used in a large number of different applications. In such light sensing applications, several characteristics of the sensing mechanism need to be in acceptable ranges and some further need to be characterized for specific light sensing applications. Other characteristics of the sensor may increase the range of applications for which the sensor is suitable and/or may provide for easier or more economical design applications. One characteristic for which general requirements vary significantly from one application to another is the angular response characteristic, i.e., the angular response profile, of the sensor which is needed for the particular application. A second characteristic is the optical gain, which for low light level measurements is preferably high enough to make stable measurements of the lowest light levels which need to be detected by the system. A third characteristic is the need to provide a relatively small, aesthetically attractive, space efficient aperture in the device for entrance of the light to be measured. A fourth characteristic is to allow substantial and preferably variable distance to separate the aperture from the electronic sensing device. A fifth characteristic is to utilize separate components to sense the light and to characterize the angular response characteristic so that the sensor may be used in a broad range of applications leading to increased standardization of the light sensing component.
Sensor devices of the type used to detect light are constructed in a variety of packages. For example, photoresistive sensors are often mounted on a circuit board with or without a separate lens positioned in front of the sensor. Some photodiodes have been constructed in which the sensor die is mounted to a lead frame and is encapsulated by a clear epoxy. A portion of the epoxy encapsulant is molded into a lens so as to focus incident light onto the sensor die. Such lenses have been either spherical or other surfaces of revolution that are symmetric about an axis which is generally perpendicular to the surface of the active sensing element. Unlike a sensor construction in which a separate lens is spaced from the sensor, the lens in these types of sensor devices is an integral part of the sensor and the space separating the sensor and the lens has been eliminated. The main design difference which results from filling the space between the lens and the sensor with plastic is that the speed of propagation of the light rays is reduced being inversely proportional to the index of refraction of the lens material. This effectively increases the focal length of the lens in proportion to the index of refraction of the material.
FIGS. 4
a
and
4
b
illustrate two general sensing configurations, each with similar angular response characteristics but with widely differing optical gains. In the first sensor configuration in
FIG. 4
a
, the sensor is close to the aperture and has desirably high optical gain. Placement of the sensor close to the aperture often leads to the added cost of additional parts and assembly processes, and longer electrical connecting paths to the sensor often compromises the electrical design. In the second sensor configuration in
FIG. 4
b
, the sensor is placed at an appreciable distance from the aperture and has undesirably low optical gain. The placement of the sensor may be convenient and less costly but for the overall design the reduction in optical gain, which may be severe, may compromise or even prevent satisfactory performance.
The angle between lines
41
a
and
42
a
and between lines
41
b
and
42
b
are the same in each of the illustrative examples and denote the nominal angle between the 50 percent response points in the optical angular response profile for each of the sensors. Light blocking portions of the housing
44
a
and
45
a
are depicted in
FIG. 4
a
in fragmentary view on opposing sides of the aperture which contains a lens
43
a
. With the sensing element
48
a
placed closer to the case than the point
49
a
of intersection of the lines
41
a
and
42
a
which depict the optical aperture, the lens, possibly combined with diffusion and/or de-focusing, may serve to decrease the viewing aperture from the angle between lines
46
a
and
47
a
to that between lines
41
a
and
42
a
as targeted by the design. The lens
43
a
serves to concentrate light impinging on the sensor thereby increasing its optical gain. Thus, the desired reduction in the overall field of view is accomplished while increasing the optical gain of the system. The general requirement for this to work with a single, thin lens in a non-light piped mode is for the sensor
48
a
to be located closer to the aperture than the apex
49
a
of the conic surface depicted by lines
46
a
and
47
a
in
FIG. 4
a
. The conic surface may be non-circular and is used only as a temporary gage for illustrative or design purposes. With the lens and/or filter removed, the conic surface is aligned in the required viewing direction and inserted as far as possible into the aperture opening which is provided. (The regions which are generally closer to the apertures than the points
49
a
or
49
b
may be referred to as the near field regions of the respective aperture.)
Light blocking portions of the housing
44
b
and
45
b
are depicted in
FIG. 4
b
in fragmentary view on opposing sides of the aperture which contains a diffusing lens and/or surface
43
b
. In this case, sensor
48
b
is farther from the aperture than the apex
49
b
. The property of point
49
b
is similar to that of
49
a
. An alternative way to describe it is as the point on the sensor side of the aperture which is the most distant point from the aperture from which the full field for which the sensor should respond to incident light or a substantial portion thereof may be seen prior to placing an optical element in the aperture. In this case, the sensor
48
b
is more distant from the aperture than the point
49
b
so that the angle between lines
46
b
and
47
b
is less than the angle between lines
41
b
and
42
b
. In three-dimensional terms, the solid angle subtended by the aperture at point
48
b
where the sensor is located is smaller than the solid angle subtended by the aperture at point
49
b
where the desired field for response to incident light may be seen through the aperture with the lens and/or filter removed. In this case, an optical element
43
b
, which has a diffusing effect, may be incorporated in the aperture and if the diffusing effect is pronounced enough to bend enough rays coming from representative directions
41
b
and
42
b
to the extent that they may strike the sensor
48
b
, a balance may be found for which the diffusing effect expands the effective viewing field from that indicated by the angle between
46
b
and
47
b
to that between
41
b
and
42
b
, as required to meet the design objective. The disadvantage is that instead of concentrating the light and adding optical gain as was accomplished in the first example, the light level is effectively attenuated because rays that would have come unobstructed through the aperture and struck the sensor before placing the diffuser in it are now spread out by the disbursing effect of the diffuser so that the proportion of the rays which reach the sensor is diminished. Accordingly, there exists the need for a sensor device construction that may be placed within a housing a distance from an aperture through the housing without sacrificing optical gain.
SUMMARY OF THE INVENTION
Accordingly, it is an aspect of the present invention to provide a sensor device that comprises: a support structure; a sensing element mounted on the support substrate for sensing optical radiation and generating an electrical output signal in response thereto; and an encapsulant encapsulating the sensing element on the support structure. The encapsulant
Bechtel Jon H.
Ockerse Harold C.
Gentex Corporation
Le Que T.
Price Heneveld Cooper DeWitt & Litton LLP
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