Infrared-rays detector

• US 6,313,462 B1
• Filed: 02/25/1999
• Issued: 11/06/2001
• Est. Priority Date: 02/27/1998
• Status: Expired due to Term

• Current Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Works Ltd (Panasonic Holdings Corporation)
• Inventors: Takada, Yuji, Matsuda, Hiroshi, Hatatani, Teruki
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): GAGLIARDI, ALBERT J
• Application Number:
  US09/257,509
• Time in Patent Office: 985 Days
• Field of Search: 250/338.1, 250/338.3, 250/338.2, 250/339.14, 250/342, 250/221, 340/567
• US Class Current: 250/338.3
• CPC Class Codes: G01J 5/14 Electrical features thereof
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: G01J 5/30 Electrical features thereof
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors

Abstract

In an infrared-rays detector, a pyroelectric element detects existence or movement of a human body, and the output signal of the pyroelectric element is converted to a voltage signal. Then, the voltage signal is subjected to waveform analysis. Then, a detection signal is outputted only when a waveform generated by a human body is detected by the waveform analysis. For example, the voltage signal is amplified at two different frequency ranges, and the amplified signals are used for discriminating a signal due to a human body. Then, a noise such as a popcorn noise of the pyroelectric element is prevented to be detected erroneously as generated by a human body.

Claims

1. An infrared-rays detector comprising:

a pyroelectric element which intermittently outputs a first current characteristic of noise caused by ambient conditions, and which outputs a second current different from the first current in the presence of a human body;

a current-to-voltage converter which converts current from said pyroelectric element to a voltage signal, said current-to-voltage converter intermittently outputting a first waveform corresponding to said first current, and outputting a second waveform corresponding to said second current and different from said first waveform in the presence of a human body; and

a signal processor which performs waveform analysis on the voltage signal received from said current-to-voltage converter and outputs a detection signal when the second waveform generated by a human body is detected by the waveform analysis but does not output a detection signal when the first waveform is detected by the waveform analysis.

2. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

an amplifier which amplifies the voltage signal received from said current-to-voltage converter;

a frequency analyzer which performs frequency analysis on an output signal of said amplifier; and

a decision circuit which detects a waveform generated by a human body based on frequency components obtained by said frequency analyzer.

3. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

a first amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range;

a second amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range different from that of said first amplifier; and

a dicision circuit which detects the waveform generated by a human body according to a ratio of amplitude levels of output signals of said first and second amplifiers.

4. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

a first amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range;

a second amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range different from that of said first amplifier;

a first comparator which compares an output signal of said first amplifier with a first threshold level;

a second comparator which compares an output signal of said second amplifier with a second threshold level; and

a decision circuit which detects the waveform generated by a human body according to comparison signals of said first and second comparators.

5. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

an amplifier which amplifies the voltage signal received from said current-to-voltage converter;

a frequency analyzer which performs frequency analysis on an output signal of said amplifier;

a decision circuit which detects the waveform generated by a human body according to time dependence of a result of the frequency analysis by said frequency analyzer.

6. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

an amplifier which amplifies the voltage signal received from said current-to-voltage converter;

a comparator which compares an output signal of said 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 said comparator detects that an output of said amplifier exceeds the threshold level.

7. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

a first amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range;

a second amplifier which amplifies the voltage signal received from said current-to-voltage converter in a frequency range different from that of said first amplifier;

a first comparator which compares an output signal of said first amplifier with a first threshold level;

a second comparator which compares an output signal of said second amplifier with a second threshold level; and

a decision circuit which measures pulse widths of output signals of said first and second comparators and detects the waveform generated by a human body according to the two pulse widths.

8. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

an amplifier which amplifies the voltage signal received from said current-to-voltage converter; and

a decision circuit which measures a rise time of an output signal of said amplifier and detects the waveform generated by a human body according to the rise time.

9. The infrared-rays detector according to claim 1, wherein said signal processor comprises:

a first amplifier which amplifies the voltage signal received from said 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 said first amplifier with a predetermined threshold to output the detection signal;

a second amplifier which amplifies the voltage signal received from said 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 said second amplifier with a threshold value to output a popcorn detection signal; and

a controller which controls at least one of said current-to-voltage converter, said first amplifier, said output circuit, said second amplifier and said popcorn noise detector to prevent that said controller outputs the detection signal when the popcorn detection signal is received from said popcorn noise detector.

10. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said current-to-voltage converter for a first predetermined time and a gain of said first amplifier for a second predetermined time longer than the first one when the popcorn detection signal is received from said popcorn noise detector.

11. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said current-to-voltage converter for a first predetermined time and prevents for said output circuit to provide an output signal for a second predetermined time longer than the first one when the popcorn detection signal is received from said popcorn noise detector.

12. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said first amplifier for a first predetermined time and prevents for said output circuit to provide an output signal for a second predetermined time longer than the first one when the popcorn detection signal is received from said popcorn noise detector.

13. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said current-to-voltage converter for a first predetermined time and a gain of said first amplifier for a second predetermined time longer than the first one and prevents for said output circuit to provide an output signal for a third predetermined time longer than the second one when the popcorn detection signal is received from said popcorn noise detector.

14. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said current-to-voltage converter for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

15. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said first amplifier for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

16. The infrared-rays detector according to claim 9, wherein said controller decreases an output signal of said output circuit for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

17. The infrared-rays detector according to claim 9, wherein said controller prevents for said first amplifier to receive an input signal for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

18. The infrared-rays detector according to claim 9, wherein said controller decreases a sensitivity to detect a popcorn signal for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

19. The infrared-rays detector according to claim 9, wherein said controller decreases a gain of said second amplifier for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

20. The infrared-rays detector according to claim 9, wherein said controller decreases a sensitivity to detect a popcorn signal by increasing a threshold of said popcorn detector for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

21. The infrared-rays detector according to claim 9. wherein said controller controls said output circuit to output a signal different from the output signal of said first voltage amplifier for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.

22. The infrared-rays detector according to claim 21, wherein the infrared-rays detector is fabricated as an integrated circuit, and the signal different from the output signal of said first voltage amplifier is a reference electric potential.

23. The infrared-rays detector according to claim 21, wherein the signal different from the output signal of said first voltage amplifier is a ground potential in a circuit of the infrared-rays detector.

24. The infrared-rays detector according to claim 21, further comprising an external electric source for driving the infrared-rays detector, wherein the signal different from the output signal of said first voltage amplifier is a potential supplied by the external electric source to said controller.

25. The infrared-rays detector according to claim 21, further comprising an oscillator, wherein an output signal of said oscillator is supplied to said controller and the signal different from the detection signal is the output voltage of said oscillator.

26. The infrared-rays detector according to claim 21, wherein said controller comprises a switch for suppplying the detection signal, and an output signal of said switch has high impedance for a predetermined time when the popcorn detection signal is received from said popcorn noise detector.