Device for detecting a human body

• US 6,366,204 B1
• Filed: 01/26/2000
• Issued: 04/02/2002
• Est. Priority Date: 05/26/1998
• Status: Expired due to Fees

• Current Assignee: Valeo Securite Habitacle (Valeo SE), Valeo Securite Habiracle
• Original Assignee: Valeo Securite Habitacle (Valeo SE)
• Inventors: Zannier, Gian
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/463,467
• Time in Patent Office: 797 Days
• Field of Search: 340/561, 340/562, 340/565, 340/567, 340/825.34, 340/825.31, 340/505, 340/5.72, 340/5.2, 307/116, 307/117, 307/10.1
• US Class Current: 340/561
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit
• CPC Class Codes: H03K 17/945 Proximity switches H03K17/96 takes precedence

Abstract

A circuit for detecting presence, includes a receiver having an antenna-forming element. An oscillator receives as input the output signal from the receiver. The oscillator includes a resonant stage and an amplification stage connected to the input of the resonant stage. The oscillator is provided with a gain such the frequency of oscillation of the signal output by the oscillator is modified when an object is in the immediate proximity of the antenna-forming element of the receiver. The circuit also includes a processor for detecting a variation in the frequency of oscillation of the signal output by the oscillator and for generating an information signal representing the detection of a presence when such a frequency variation is detected.

Claims

1. A circuit for detecting presence comprising:

a receiver having an antenna-forming element;

an oscillator receiving an output signal from said receiver, said oscillator generating an output signal having a frequency of oscillation, the oscillator including a resonant stage having an input and an amplification stage coupled to the input of said resonant stage and providing said oscillator with gain such that the frequency of oscillation of the signal output by the oscillator is modified when an object is in the immediate proximity of the antenna-forming element of the receiver; and

a processor for detecting a variation in the frequency of oscillation of the signal output by the oscillator and for generating an information signal representing the detection of a presence when such a frequency variation is detected.

2. A circuit according to claim 1, wherein the amplification stage provides the oscillator with gain of the order of or greater than 10⁵, at least for a frequency lying in the range 100 Hz to 500 Hz.

3. A circuit according to claim 1, wherein an input of the amplifier stage is connected to the output of the receiver via a first resistor, and wherein the amplifier stage has at least one branch which is connected in parallel with said resistor and which comprises at least three logic inverters in cascade.

4. A circuit according to claim 3 wherein the logic inverters are amplifiers comprising inverting logic gates having push-pull type output circuits.

5. A circuit according to claim 3, wherein a second resistor is connected between the output of the receiver and the three logic inverters in cascade.

6. A circuit according to claim 5, wherein the first and second resistors have resistances such that at least the first logic inverter operates in non-saturated mode.

7. A circuit according to claim 6, wherein the non-saturated logic inverter is followed by at least one pair of saturated logic inverters.

8. A circuit according to claim 3, wherein a resistor is connected in parallel with the terminals of each of the logic inverters in cascade.

9. A circuit according to claim 1, wherein the processor includes a comparator programmed to compare a predetermined threshold value with the mean value of a signal representative of variation in the frequency of the signal output by the resonant stage.

10. A circuit according to claim 9, wherein the comparator comprises a logic inverter having an input connected to the input of said comparator via a unipolar switch, a capacitor connected between a power supply line and the input of said logic inverter, and a resistor connected in series with a second unipolar switch between the input of said logic inverter and the ground line.

11. A circuit according to claim 9 wherein the comparator includes an adaptive threshold comparator circuit (R, C, COMP).

12. A circuit according to claim 1, wherein the resonant stage comprises a logic inverter connected between the input and the output of said oscillator, and a capacitor and resistor connected in series between the output of said receiver and the output of the resonant stage.

13. A circuit according to claim 1, wherein the processor comprises an integrator connected to the output of the resonant stage.

14. A circuit according to claim 13, wherein said integrator comprises a logic inverter having an input connected to the input of said integrator via a unipolar switch, and a capacitor connected between the input of said logic inverter and a ground line.

15. A circuit according to claim 14, wherein said integrator further comprise a variable resistor connected between the input of said fifth logic inverter and said ground line.

16. A circuit according to claim 1, wherein the receiver includes a capacitive filter.

17. A circuit according to claim 1, wherein the information signal includes an interrogation signal that activates a remote device when presence is detected.

18. A circuit for detecting presence, comprising:

means for receiving an intrinsic electromagnetic field radiated by a human body;

an amplifying circuit, including an amplifying stage and a resonant stage, wherein the field received by said receiver means is injected in the resonant stage via the amplifying stage for amplification and conversion, the amplifying circuit generating a signal having at least one parameter that is correlated with the intensity of said received electromagnetic field; and

a comparator, programmed to receive said signal and to compare said parameter with a threshold value representative of the presence being detected.