Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-02-25
2001-11-06
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C340S567000
Reexamination Certificate
active
06313462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared-rays detector for detecting infrared energy radiated from a human body in order to detect the existence or movement of a human body.
2. Description of the Prior Art
A pyroelectric element is used widely to detect infrared-rays radiated from a human body. The pyroelectric element set for each of monitor areas outputs a current in correspondence to infrared radiation. Then, in an infrared-rays detector, a current-to-voltage converter converts the current to a voltage, and a voltage amplifier amplifies the voltage. When the output voltage exceeds a predetermined level, it is decided that a human body is detected, and a detection signal which means that a human body exists or moves in the monitor area is outputted.
The infrared-rays detector is designed to have the frequency characteristic for movement of a human body, and it has a characteristic of band-pass filter having a center of transmission band at about 1 Hz. Then, the sensitivity to a human body is enhanced, and a malfunction is prevented to be caused by signals at frequencies irrelevant to movement of a human body.
However, the pyroelectric element outputs a one-shot noise called as popcorn noise disadvantageously. It is thought that the popcorn noise is ascribed to generation of unnecessary electric charges in the pyroelectric element, and the unnecessary electric charges are generated by compression or tensile stress centered at defects in materials of a pyroelectric plate or electrodes or at pitchings, microcracks or the like generated by dicing or the like, due to differences in thermal expansion coefficient in a pyroelectric plate, electrodes, a support, an adhesive agent, a circuit board or the like in the pyroelectric element.
Previously, in order to reduce the occurrence of the popcorn noise as one-shot output noise, it is proposed to optimize the materials for the support, the circuit board, the electrically conductive adhesive, or the like, or to change the structure of the pyroelectric element. However, even if such proposals are adopted, the occurrence of the popcorn noise cannot be suppressed completely in the infrared-rays detector, and a malfunction is liable to be caused by the popcorn noise.
SUMMARY OF THE INVENTION
The invention intends to solve the problems and its object is to provide an infrared-rays detector which does not operate erroneously when a popcorn noise occurs.
An infrared-rays detector according to the invention comprises a pyroelectric element, a current-to-voltage converter which converts a current from the pyroelectric element to a voltage signal, and a signal processor which performs waveform analysis on the voltage signal received from the current-to-voltage converter and outputs a detection signal only when a waveform generated by a human body is detected by the waveform analysis. The signal processor may be realized in various ways as explained below.
For example, the signal processor comprises an amplifier which amplifies the voltage signal received from the current-to-voltage converter, a frequency analyzer which performs frequency analysis on an output signal of the amplifier, and a decision circuit which detects a waveform generated by a human body based on frequency components obtained by the frequency analyzer.
For example, the signal processor comprises a first amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range, and a second amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range different from that of the first amplifier, and a decision circuit which detects the waveform generated by a human body according to a ratio of amplitude levels of output signals of the first and second amplifiers.
For example, the signal processor comprises a first amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range, a second amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range different from that of the first amplifier, and a first comparator which compares an output signal of the first amplifier with a first threshold level, a second comparator which compares an output signal of the second amplifier with a second threshold level, a decision circuit which detects the waveform generated by a human body according to comparison signals of the first and second comparators.
For example, the signal processor comprises an amplifier which amplifies the voltage signal received from the current-to-voltage converter, and a frequency analyzer which performs frequency analysis on an output signal of the amplifier, and a decision circuit which detects the waveform generated by a human body according to time dependence of a result of the frequency analysis by the frequency analyzer.
For example, the signal processor comprises an amplifier which amplifies the voltage signal received from the current-to-voltage converter, a comparator which compares an output signal of the first amplifier with a threshold level, and a decision circuit which detects the waveform generated by a human body according to a length of time when the comparator detects that an output of the amplifier exceeds the threshold level.
For example, the signal processor comprises a first amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range, a second amplifier which amplifies the voltage signal received from the current-to-voltage converter in a frequency range different from that of the first amplifier, a first comparator which compares an output signal of the first amplifier with a first threshold level, a second comparator which compares an output signal of the second amplifier with a second threshold level, a decision circuit which measures pulse widths of output signals of the first and second comparators and detects the waveform generated by a human body according to the two pulse widths.
For example, the signal processor comprises an amplifier which amplifies the voltage signal received from the current-to-voltage converter, and a decision circuit which measures a rise time of an output signal of the amplifier and detects the waveform generated by a human body according to the rise time.
For example, the signal processor comprises a first amplifier which amplifies the voltage signal received from the current-to-voltage converter with a first band-pass filter characteristic having a center of transmission band at a first frequency, an output circuit which compares an output signal of the first amplifier with a predetermined threshold to output the detection signal, a second amplifier which amplifies the voltage signal received from the current-to-voltage converter with a second band-pass filter characteristic having a center of transmission band at a second frequency higher than the first frequency, a popcorn noise detector which compares an output signal of the second amplifier with a threshold value to output a popcorn detection signal, and a controller which controls at least one of the current-to-voltage converter, the first amplifier, said output circuit, the second amplifier and the popcorn noise detector to prevent that the controller outputs the detection signal when the popcorn detection signal is received from the popcorn noise detector. For example, when the popcorn detection signal is received from the popcorn noise detector, the controller decreases a gain of the current-to-voltage converter for a predetermined time, decreases a gain of the first amplifier for a predetermined time, or the controller decreases an output signal of the output circuit for a predetermined time, decreases a gain of the second amplifier for a predetermined time, or decreases a sensitivity to detect a popcorn signal by increasing a threshold of the popcorn detector for a predetermined time. When the controller controls at least two of them, a component located i
Hatatani Teruki
Matsuda Hiroshi
Takada Yuji
Gagliardi Albert
Greenblum & Bernstein P.L.C.
Hannaher Constantine
Matsushita Electric & Works Ltd.
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