Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-10-07
2001-09-25
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338400, C250S334000
Reexamination Certificate
active
06294783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared sensor and, more particularly, to a pyroelectric infrared sensor to be used in, for example, a burglar alarm or security system for the purpose of detecting a person.
2. Description of the Related Art
FIG. 11
is a circuit diagram showing the basic circuitry of an infrared sensor. The infrared sensor generally denoted by
1
has a pyroelectric element
2
. The pyroelectric element
2
has, for example, a pyroelectric substrate and electrodes formed on both surfaces of the pyroelectric substrate. An example is described below in connection with FIG.
12
. Thus, a pair of pyroelectric bodies polarized in opposite directions as indicated by arrows in
FIG. 11
are connected in series to form the pyroelectric element. A resistor or equivalent resistance is connected in parallel with the series connection of the pyroelectric elements. The pyroelectric element
2
has one terminal connected to the gate G of a field effect transistor (FET)
3
and the other terminal connected to the ground GND. The drain D and the source S of the FET
3
serve as the input and output terminals of the infrared sensor
1
.
In the operation of this infrared sensor
1
, the pyroelectric element
2
supplied with thermal energy generates pyroelectric current that is output as a voltage through an impedance transformation effected by the resistor and the FET
3
. The infrared sensor
1
is sensitive even to a very low intensity of infrared rays. The high sensitivity to small energy input, on the other hand, poses a problem in that the infrared sensor
1
is not stable against external noise. In particular, the infrared sensor
1
is liable to be affected by RF noise of frequencies ranging from 100 MHz to 2 GHz, resulting in malfunction. In order to eliminate such RF noise, Japanese Laid-Open Patent Publication No. 60-125530 discloses a circuit in which capacitors are connected between the drain D of the FET
3
and the ground GND and between the source S and the ground GND of the FET
3
.
In general, an infrared sensor of the kind described can have a structure as illustrated in FIG.
12
. The infrared sensor
1
has a stem
4
that serves also as a case. The stem
4
has a disk-shaped metallic base
4
a
and three terminals
4
b,
4
c
and
4
d
extending from the metallic base
4
a
. The terminal
4
d
of these three terminals
4
b,
4
c,
4
d
is electrically connected to the metallic base
4
a
, while other terminals
4
b,
4
c
are insulated from the metallic base
4
a
. These terminals
4
b,
4
c,
4
d
are formed so as to project upward above the metallic base
4
a.
A substrate
5
rests on the metallic base
4
a
. Pattern electrodes
6
a,
6
b,
6
c
and
6
d
are formed on the upper surface of the substrate
5
. Holes are formed in the portions of the substrate
5
where the pattern electrodes
6
a,
6
b,
6
c
are formed, and the aforesaid terminals
4
a
,
4
b,
4
c
are received in these holes. The grounding terminal
4
d
is connected to the pattern electrode
6
a,
while the electrodes
4
b
and
4
c
are respectively connected to the pattern electrodes
6
b
and
6
c.
To the pattern electrode
6
d
is connected the gate G of the FET
3
, while the pattern electrodes
6
b,
6
c
are connected to the drain D and the source S of the FET
3
. Capacitors
7
are connected, respectively, between the pattern electrodes
6
a
and
6
b
and between the pattern electrodes
6
a
and
6
c.
A pyroelectric element
2
is connected to the pattern electrodes
6
a
and
6
d,
through supports
8
made of an electrically conductive material. The described structure is capped with a cap
9
that has an infrared-transmissive filter.
In this infrared sensor
1
, RF noise is removed by the capacitors
7
connected between the drain D of the FET
3
and the ground GND and between the source S of the FET
3
and the ground GND, whereby malfunctioning attributable to the RF noise is suppressed.
However, resistance and inductance are generated in the pattern electrodes and terminals on the substrate. Similarly, resistance and inductance are formed also in the grounding terminal, between the metallic base and the substrate. Consequently, the infrared sensor
1
has a circuit as shown in
FIG. 13
that fails to stably remove RF noise due to resistance and inductance generated in the pattern electrodes and the terminals.
It is also to be noted that reduction in size of the substrate is not easy because of the necessity of providing the capacitors on the substrate. Moreover, the use of the capacitors raises the cost. For these reasons, the anti-noise measure employing capacitors can be used only for certain types of products that tolerate high price.
For the foregoing reasons, there is a need for an inexpensive infrared sensor that can stably remove RF noise and that is easy to miniaturize.
SUMMARY OF THE INVENTION
The present invention is directed to an infrared sensor which satisfies the aforementioned need. The infrared sensor comprises: a stem having a metallic base serving as a ground and a terminal extending from the metallic base; a substrate disposed on the metallic base; a field effect transistor attached to the substrate; a pyroelectric element connected between the gate of the field effect transistor and the ground; and a capacitor connected between ground and either or both of the drain terminal and the source terminal of the field effect transistor. One of the electrodes of the capacitor is directly connected to the metallic base of the stem, while the other electrode of the capacitor is directly connected to the respective terminal by a conductive bonding material.
In this infrared sensor, the arrangement may be such that one of the electrodes of the capacitor is connected to a flat surface portion of the metallic base and the other electrode of the capacitor is connected to the terminal, and the capacitor is disposed at a vertical lateral face presented by the substrate.
The capacitor may also be disposed in a hole or recess formed in the substrate.
The infrared sensor may further comprise an insulating spacer provided between the metallic base and the substrate.
The arrangement also may be such that a protuberance is formed on the metallic base of the stem, and wherein the one of the electrodes of the capacitor is connected to the protuberance while the other electrode of the capacitor is connected to the terminal, at the upper side of the substrate.
The direct connection between one of the electrodes of the capacitor and the metallic base serves to reduce the influence of resistance and inductance generated in the portion of the grounding terminal between the substrate and the metallic base. The direct connection between the other electrode of the capacitor and the terminal by the conductive bonding material serves to reduce the influence of resistance and inductance generated in pattern electrodes. The resistance and inductance generated in the terminal connected to the other electrode of the capacitor forms, together with the capacitance of the capacitor connected in parallel therewith, a tank circuit which effectively accumulates RF noise.
The direct connection between one of the electrodes of the capacitor and the metallic base eliminates the necessity of laying a pattern electrode over a substantial length on the substrate from the capacitor electrode to the terminal that is necessary in the known art, thus contributing to a reduction in the size of the substrate. This facilitates miniaturization of the infrared sensor, and thus offers a reduction in the price of the infrared sensor.
For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
REFERENCES:
patent: 4626687 (1986-12-01), Nara et al.
patent: 5352895 (1994-10-01), Inoue
patent: 19616549 (1997-09-01), None
patent: 0145457 (1985-06-01), None
patent: 0362
Hannaher Constantine
Israel Andrew
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
LandOfFree
Infrared sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Infrared sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Infrared sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491740