Photodetector

Abstract: A photodetector (K1-K5) including a reception portion (1) and a shield casing (2) for performing electro­ magnetic shielding of the reception portion (1), in which a light receiving window (3) confronting the reception portion (1) is formed on the shield casing (2) convexly in a direc­ tion away from the reception portion (1) and a plurality of holes (4) for directing light signals (5) towards the reception portion (1) are formed on a peripheral surface of the light receiving window (3).

Description: BACKGROUND OF THE INVENTION The present invention relates to a photodetector for use in a remote-control apparatus employing near infrared rays, etc. as control signals, for example, a remote-control unit of a television set, a video tape recorder or the like. Conventionally, a reception portion of a wireless remote-control system based on near infrared rays is constituted by a photosensor (photoelectric conversion device), an amplification circuit, a detection circuit, a waveform shaping circuit, etc. This reception portion handles extremely weak electric signals and therefore, is readily affected by noises produced by electrostatic induction or electromagnetic induction inside and outside the wireless remote-control system, so that operation of the reception portion becomes unstable. Thus, the reception portion is enclosed by a shield casing such that entry of noises into the reception portion is restricted by the shield casing. However, in order to receive electric signals by the photosensor, a window for receiving light is required to be provided on the shield casing. Hence, in order to prevent entry of noises into the reception portion through the window, various countermeasures shown in Figs. 1 to 5 have been taken so far. In Fig. 1, a light receiving window 3 is formed as small as possible on a front face of a shield casing 2 of a reception portion 1. In Fig. 2, the light receiving window 3 is constituted by a conductive metal gauze. In Fig. 3, the light receiving window 3 is constituted by a plurality of slits as disclosed in Japanese Utility Model Publication (examined) No. 23182/1987. Meanwhile, in Figs. 4 and 5, the light receiving window 3 on the front face of the shield casing 2 is constituted by a plurality of holes 4. However, in the known arrangement of Fig. 1, since diameter of the light receiving window 3 cannot be made so small due to restriction of directivity characteristics of the reception portion 1, the shield casing 2 cannot shield the reception portion 1 fully from noises. In the known arrangement of Fig. 2, directivity characteristics are inferior. Furthermore, in the known arrangement of Fig. 2, since the light receiving window 3 is constituted by the metal gauze separate from the shield casing 2, its production cost becomes high. Meanwhile, in the known arrangement of Fig. 3, since the slits extend longitudinally in the vertical direction of the shield casing 2 and opposite sidewalls of each of the slits are directed towards the photosensor, directivity characteristics for light signals proceeding in the lateral direction of the shield casing 2 are excellent but directivity characteristics for light signals proceeding in the vertical direction of the shield casing 2 becomes poor. Furthermore, in the known arrangement of Figs. 4 and 5, since areas of the holes effective against light signals 5 proceeding obliquely relative to the front face of the shield casing 2 are substantially reduced as shown in Fig. 5, amount of the light signals 5 received by a photosensor 6 is reduced, thereby resulting in deterioration of its directivity characteristics. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide, with a view to eliminating the disadvantages inherent in conventional photodetectors, a photodetector which achieves excellent shielding effects against noises and has improved directivity characteristics. As shown in Figs. 6 and 7, in order to accomplish this object of the present invention, a photodetector embodying the present invention includes a reception portion 1 and a shield casing 2 for performing electromagnetic shield of said reception portion 1, the improvement comprising: a light receiving window 3 which is formed on said shield casing 2 convexly in a direction away from said reception portion 1 so as to confront said reception portion 1 and a plurality of holes 4 which are formed on a peripheral surface of said receiving window 3 as to direct light signals 5 towards said reception portion 1. In the photodetector of the present invention, the light signals 5 of near infrared rays transmitted from a remote-control transmitter pass through the holes 4 of the light receiving window 3 to a sensor chip 7 of a photosensor 6. At this time, entry of noises into the shield casing 2 takes place more readily as diameter of the holes 4 is made larger. On the contrary, shielding effects of the shield casing 2 against noises are enhanced as diameter of the holes 4 is made smaller. In the photodetector of the present invention, since a plurality of the holes 4 are formed on the light receiving casing 3, not only a required amount of the light signals 5 can be passed through the holes 4 but shielding effects of the shield casing 2 against noises can be improved. Moreover, in the photodetector of the present invention, since the light receiving window 3 is formed convexly in the direction away from the reception portion 1 and the holes 4 are formed on the surface of the light receiving window 3 such that opposite sidewalls 4a of each of the holes 4 are directed towards the photosensor 6, even the light signals 5 proceeding obliquely relative to the front face of the shield casing 2 can be received by the photosensor 6 even if the holes 4 have a small diameter. Therefore, in the photodetector of the present invention, since reduction of areas of the holes 4 effective against the light signals proceeding obliquely relative to the front face of the shield casing 2 can be restricted, a region enabling remote control can be expanded remarkably through improvement of its directivity characteristics. BRIEF DESCRIPTION OF THE DRAWINGS This object and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Figs. 1 to 4 are perspective views of prior art photodetectors, respectively (already referred to); Fig. 5 is a fragmentary sectional view taken along the line V-V in Fig. 4 (already referred to); Fig. 6 is a perspective view of a photodetector according to a first embodiment of the present invention; Fig. 7 is a fragmentary sectional view taken along the line VII-VII in Fig. 6; Figs. 8 and 9 are front elevational views of light receiving windows employed in photodetectors according to second and third embodiments of the present invention, respectively; Fig. 10 is a view similar to Fig. 7, particularly showing a fourth embodiment of the present invention; and Fig. 11 is a view similar to Fig. 6, particularly showing a fifth embodiment of the present invention. Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is shown in Figs. 6 and 7, a photodetector K1 for use in a remote-control apparatus, according to a first embodiment of the present invention. The photodetector K1 includes a reception portion 1 and a shield casing 2 for performing electromagnetic shielding of the reception portion 1 and a light receiving window 3. The light receiving window 3 is formed integrally with a front face 8 of the shield casing 2 and confronts the reception portion 1 so as to be projected convexly in a direction away from the reception portion. Furthermore, a plurality of circular holes 4 are so formed on a whole surface of the light receiving window 3 as to direct light signals 5 towards the reception portion 1. The reception portion 1 is constituted by a photosensor 6, an amplification circuit, a detection circuit, a waveform shaping circuit, etc. The photosensor 6 is constituted by a photodiode and includes a sensor chip (photodiode chip) 7. The photosensor 6 is disposed rearwards of the light receiving window 3. The shield casing 2 is made of electrically conductive material and has a shape of rectangular parallelepiped. In order to shield the reception portion 1 from noises produced through electrostatic induction or electromagnetic induction inside and outside the remote-control apparatus, the reception portion 1 is accommodated in the shield casing 2. The convex surface of the light receiving window 3 has a hemispherical shape. A plurality of the circular holes 4 are formed on the light receiving window 3 so as to be distributed radially with the vertex of the hemispherical surface of the light receiving window 3 as the center. Each of the holes 4 is of such a diameter of, for example, 1.2 mm as to sufficiently reduce entry of noises into the shield casing 2 and the number of the holes 4 is set to such a value as to secure a necessary amount of the light signals 5 for the reception portion 1. Moreover, opposite sidewalls 4a of each of the holes 4 are formed in a direction perpendicular to the hemispherical surface of the light receiving window 3 so as to be directed towards the photosensor 6 of the reception portion 1. In the above described arrangement of the photodetector K1, the light signals 5 of near infrared rays transmitted from a remote-control transmitter pass through the holes 4 of the light receiving window 3 into the shield casing 2 and are converted into electric signals by the sensor chip 7 of the photosensor 6 so as to be outputted to a signal decoding circuit via the amplification circuit, the detection circuit, etc. At this time, entry of noises into the shield casing 2 occurs more readily as diameter of the holes 4 is increased. On the contrary, shielding effects of the shield casing 2 against noises are enhanced as diameter of the holes 4 is reduced. In the photodetector K1, since a plurality of the holes 4 are formed on the light receiving window 3, a necessary amount of the light signals 5 for the reception portion 1 can be passed through the holes 4 and shielding effects of the shield casing 2 against noises can be improved. Meanwhile, in the photodetector K1, the light receiving window 3 is formed convexly. In addition, the holes 4 are formed on the whole surface of the light receiving window 3 and the opposite sidewalls 4a of each of the holes 4 are formed in the direction perpendicular to the hemispherical surface of the light receiving window 3 so as to be directed towards the photosensor 6. Therefore, in the photodetector K1, even if diameter of the holes 4 is small, even the light signals 5 travelling obliquely relative to the front face 8 of the shield casing 2 can be received by the photosensor 6. As described above, in the photodetector K1, since reduction of areas of the holes 4 effective against the light signals 5 proceeding obliquely relative to the front face 8 of the shield casing 2 can be restricted, reduction of amount of the light signals 5 to be inputted to the photosensor 6 is lessened, so that a region enabling remote control can be expanded extraordinarily through improvement of its directivity characteristics. Therefore, in the light receiving window 3 of the photodetector K1, the optical signals proceeding obliquely relative to the front face of the shield casing 2 can be supplied to the photosensor 6 with a small loss and the reception portion 1 can be sufficiently shielded from external noises, so that remote control of the remote-control apparatus can be performed stably. Meanwhile, the photodetector of the present invention is not restricted to that of the above embodiment but can be modified variously. For example, as shown in Fig. 8, the light receiving window 3 is not restricted to the hemispherical shape but can be formed into a shape of a polygonal pyramid in a photodetector K2 according to a second embodiment of the present invention. Meanwhile, as shown in Fig. 9, each of the holes 4 of the light receiving window 3 is not restricted to circular shape but can be replaced by an elongated opening extending radially with the vertex of the convex surface of the light receiving window 3 as its center in a photodetector K3 according to a third embodiment of the present invention. Furthermore, as shown in Fig. 10, the opposite sidewalls 4a of each of the holes 4 are not so restricted as to be formed in the direction perpendicular to the hemispherical surface of the light receiving window 3 but can be formed, in parallel with each other, in a direction perpendicular to the front face 8 of the shield casing 2 in a photodetector K4 according to a fourth embodiment of the present invention. In the photodetector K4, the holes 4 can be machined more easily than the photodetector K1. Referring finally to Fig. 11, there is shown a photodetector K5 according to a fifth embodiment of the present invention. In the photodetector K5, a plurality of the holes 4 are formed along a circular base of the hemispherical surface of the light receiving window 3 and a pair of semicircular openings 10 separated from each other by a rib 11 are formed at the vertex of the hemispherical surface of the light receiving window 3. Since other constructions of the photodetector K5 are similar to those of the photodetector K1, description thereof is abbreviated for the sake of brevity. In addition, the light receiving window 3 is not necessarily required to be formed integrally with the shield casing 2 but can also be provided separately from the shield casing 2. As is clear from the foregoing, in the photodetector of the present invention, the light receiving window confronting the reception portion is convexly formed on the shield casing and a plurality of the holes are so formed on the surface of the light receiving window as to direct the light signals towards the reception portion. Accordingly, in accordance with the present invention, shielding effects of the shield casing against noises produced inside and outside the remote-control apparatus are enhanced and a wide remote-control region can be obtained through improvement of directivity characteristics. Furthermore, in accordance with the present invention, since shielding effects of the shield casing against noises are enhanced, the reception portion can be disposed in close vicinity to the noise sources, thus resulting in saving of space required for the remote-control apparatus. Moreover, in accordance with the present invention, since the light receiving window is obtained by machining the shield casing itself, such an excellent effect as reduction of production cost of the photodetector can be achieved.

Claims: A photodetector (K1-K5) including a reception portion (1) and a shield casing (2) for electromagnetic shielding of said reception portion (1) comprising: a light receiving window (3) formed on said shield casing (2) convexly in a direction away from said reception portion (1) so as to face said reception portion (1); and a plurality of holes (4) formed on the surface of said light receiving window (3) to direct light signals (5) towards said reception portion (1). A photodetector (K1, K3-K5) as claimed in Claim 1, wherein the convex surface of said light receiving window (3) has a hemispherical shape. A photodetector (K1, K4, K5) as claimed in Claim 2, wherein each of said holes (4) has a circular shape. A photodetector (K1, K5) as claimed in Claim 2, wherein said holes (4) are formed in a direction perpendicular to the hemispherical surface of said light receiving window (3). A photodetector (K1, K5) as claimed in Claim 3, wherein said holes (4) are formed in a direction perpendicular to the hemispherical surface of said light receiving window (3). A photodetector (K2, K3) as claimed in Claim 1, wherein the convex surface of said light receiving window (3) has the shape of a polygonal pyramid. A photodetector (K3) as claimed in Claim 2, wherein each of said holes (4) is constituted by an elongated opening extending radially from the vertex of the hemispherical surface of said light receiving window (3). A photodetector (K3) as claimed in Claim 6, wherein each of said holes (4) is constituted by an elongated opening extending radially from the vertex of the polygonal pyramid of said light receiving window (3). A photodetector (K4) as claimed in Claim 2, wherein said light receiving window (3) is formed on a face (8) of said shield casing (2) and said holes (4) are formed in a direction perpendicular to said face (8) of said shield casing (2). A photodetector (K4) as claimed in Claim 3, wherein said light receiving window (3) is formed on a face (8) of said shield casing (2) and said holes (4) are formed in a direction perpendicular to said face (8) of said shield casing (2). A photodetector (K5) as claimed in Claim 3, wherein said holes (4) are formed along a circular base of the hemispherical surface of said light receiving window (3) and a pair of semicircular openings (10) are formed at a vertex of the hemispherical surface of said light receiving window (3).

Inventors: YOKOTA SHOUJI, YOKOTA, SHOUJI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1989
Main classification: H01L31
IPC codes: G11B33, H04Q9, H01L31, H04B10, H04N5