Optical receiver

Details Optical receiver Optical receiver

1998-02-24

2001-03-27

Chan, Jason (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200, C257S458000, C257S461000

Reexamination Certificate

active

06208447

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention generally relates to optical receivers and it particularly pertains to the technology of optical receivers for use in optical remote control receivers operable to perform conversion of optical signals transmitted from the optical remote controller into electrical signals.
A typical optical remote control receiver is made up of an optical receiver, such as a photodiode (PD), operable to convert an optical signal into an electric current, and a peripheral circuit operable to convert a photocurrent produced in the optical receiver when light falls thereupon into a signal distinguishable by a logic circuit such as microcomputer.
Generally speaking, as the distance between the optical receiver and the transmitter, i.e., the receiving distance, increases, the optical receiver receives weaker light. Stated another way, as the photodetection sensitivity of an optical remote control receiver increases, its receiving range likewise increases. Conversely, as the photodetection sensitivity decreases, the receiving range likewise decreases. The long receiving range provides some advantages. For example, one advantage is that the transmitter may reduce its optical signal output for the electric battery to last for a longer time. Another advantage is that improvements in handling can be made.
Accordingly, there have been strong demands in the market for optical remote control receivers having a receiving range of 10 meters or more. Demand for high-performance optical receivers superior in photodetection sensitivity is therefore high.
Optical remote control receivers generally have domestic uses, which means that their photodetection sensitivity is greatly affected by the existence of electromagnetic noise from, for example, fluorescent lamps. In other words, the optical remote control receiver receives electromagnetic noise in addition to optical signals transmitted from a transmitter. The received optical signals are lost in the noise, leading to a drop of the photodetection sensitivity.
With a view to getting rid of such unwanted electromagnetic noise, various approaches have been made to optical receivers.
For example, Japanese Patent Application Laying Open Gazette No. 6-69409 shows a technique that the entirety of an optical receiver is shielded from electromagnetic noise by a metallic shell. Japanese Patent Application Laying Open Gazette No. 6-291356 shows a technique that a light-transmissive conductive film is formed on the surface of a light receiving section. Japanese Patent Application Laying Open Gazette No. 2-275680 shows a technique that the entire light receiving surface of a photodiode is shielded by a diffused region. Japanese Utility Model Application Laying Open Gazette No. 4-40553 shows a technique that only an area of the light receiving surface in the vicinity of a noise source is shielded by a diffused layer.
The above-listed prior art techniques are problematic in the following aspects. The technique of shielding the entirety of an optical receiver from electromagnetic noise is unattractive in the aspect of dimensions as well as in the aspect of costs. The technique of forming a light-transmissive conductive film on the light receiving surface is not attractive, either, for the reason that although the conductive film is a trans illuminous film its transmission rate is not 100%. Accordingly, there exist limits of improving the sensitivity of photodetection. Preferable dimensions, costs, and photodetection sensitivity would be best achieved by the technique of shielding a light receiving surface by a diffused layer.
Even such a technique is problematic. Although the technique may achieve a reduction of the effect of electromagnetic noise, such achievement will not much contribute to providing an improved photodetection sensitivity. It is hard to provide a receiving range in excess of 10 meters. Additionally, it is almost impossible to locate an electromagnetic noise source in general homes, and it is therefore practically impossible to shield only a near-noise source area of the light receiving surface by diffused layer.
Having conducted examinations based on experiments, the inventors of the present invention discovered that there occurs spontaneous noise in optical receivers due to the contact of a light receiving layer and a diffused layer used to shield the light receiving layer. Such spontaneous noise is a new bar to improvement in the optical receiver photodetection sensitivity.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an optical receiver superior to conventional ones in photodetection sensitivity and capable of providing a longer receiving range for optical remote control receivers.
The present invention provides an optical receiver comprising:
a semiconductor substrate of one conductivity type; and
a light receiving section which is an impurity region of opposite conductivity type formed in an upper surface area of said semiconductor substrate;
said optical receiver further comprising:
a first shield section which is an impurity region of said one conductivity type formed in an upper surface area of said light receiving section for providing protection against electromagnetic noise;
wherein said shield section is formed in such a way as to provide a partial covering of the upper surface of said light receiving section for preventing an excessive occurrence of spontaneous noise due to contact with said light receiving section.
In accordance with the present invention, the first shield section partially covers the surface of the light receiving section in order to prevent an excessive occurrence of spontaneous noise caused by contact with the light receiving section. As a result of such arrangement, spontaneous noise is not produced to such an extent that it becomes a bar to improving the sensitivity of photodetection of optical receivers. An improved photodetection sensitivity is achieved. The receiving range of optical remote control receivers can be increased. This allows a transmitter to reduce its output for the electric battery to last for a longer time and makes improvements in handling.
In the foregoing optical receiver, it is preferred that a second shield section of an impurity region of the one conductivity type is formed around the light receiving section in the semiconductor substrate upper surface area.
As a result of such arrangement, electromagnetic noise incident on upper surface areas of the semiconductor substrate other than the light receiving section upper surface can be shielded by the second shield section.
It is preferred that the first and second shield sections are electrically connected with each other.
Such arrangement eliminates the need for providing a shield electrode for connecting the first shield section to ground on the first shield section, which allows the shield electrode to be formed on the second shield section. As a result, the upper surface of the light receiving section is not light-shielded. The upper surface of the light receiving section is effectively used as a light receiving surface.
It is preferred that the second shield section has a lateral shield portion which is formed deeper than the light receiving section.
As a result of such arrangement, electromagnetic noise incident on the sideface of the light receiving section can be cut off by the lateral shield portion formed deeper than the light receiving section.
It is preferred that a contact layer which is an impurity region of the one conductive type is formed in a lower surface of the semiconductor substrate, wherein almost all of the lower surface of the semiconductor substrate is bonded to a lead with a conductive adhesive.
As a result of such arrangement, electromagnetic noise incident upon the lower surface of the semiconductor substrate is positively cut off by the lead.
It is preferred that at least a lower part of the sideface of the semiconductor substrate is covered with the conductive adhesive.
As a result of such arrangement, electromagnetic noise incident upo

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