Capacitive sensing isolation using reversed biased diodes

• US 7,521,940 B2
• Filed: 01/26/2007
• Issued: 04/21/2009
• Est. Priority Date: 01/26/2006
• Status: Expired due to Fees

• Current Assignee: TK Holdings Incorporated (Ningbo Junsheng Investment Group Co., Ltd.)
• Original Assignee: TK Holdings Incorporated (Ningbo Junsheng Investment Group Co., Ltd.)
• Inventors: Koch, Stu, Maguire, Phil
• Primary Examiner(s): Nguyen; Vincent Q
• Application Number:
  US11/698,275
• Publication Number:
  US 20070208529A1
• Time in Patent Office: 816 Days
• Field of Search: 324/658, 324/661, 324/672, 324/76.11
• US Class Current: 324/661
• CPC Class Codes: B60N 2/002 Seats provided with an occupancy detection means mounted therein or thereon detection means responsive to presence or absence of children B60N2/266
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• CPC Class Codes: B60R 21/0154 in combination with seat heating
• CPC Class Codes: G01D 21/02 Measuring two or more variables by means not covered by a single other subclass
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01G 19/4142 for controlling activation of safety devices, e.g. airbag systems electrical circuits for triggering safety arrangements in case of vehicle accidents B60R21/015
• CPC Class Codes: G01G 7/06 by electrostatic action
• CPC Class Codes: G01L 1/144 with associated circuitry G01L1/146 and G01L1/148 take precedence

Abstract

A capacitive sensor is provided. The capacitive sensor includes a sensor/heat pad for outputting a sensing signal, a first diode coupled to a first node of the sensor/heat pad, a second diode coupled to a second node of the sensor/heat pad, a first transistor coupled to the first diode and a second transistor coupled to the second diode. During a sensing mode, the first and second transistors are opened and a reverse-biased signal is applied to the first diode and the second diode so that the sensor/heat pad is isolated from the first and second transistors.

Claims

1. A sensor, comprising:

a sensor/heat pad for outputting a sensing signal;

a first diode coupled to a first node of the sensor/heat pad;

a second diode coupled to a second node of the sensor/heat pad;

a first transistor coupled to the first diode; and

a second transistor coupled to the second diode, wherein during a sensing mode, the first and second transistors are opened and a reverse-biased signal is applied to the first diode and the second diode so that the sensor/heat pad is isolated from the first and second transistors.

2. A sensor as claimed in claim 1, further comprising:

a power source coupled to the first transistor and wherein the second transistor is coupled to ground.

3. A sensor as claimed in claim 2, wherein during a heating mode, the first and second transistors are closed and a current flows from the power source to ground.

4. A sensor as claimed in claim 1, wherein the sensing signal is sinusoidal.

5. A sensor as claimed in claim 1, wherein during the sensing mode a buffered sensing signal with a DC offset less than the sensing signal is applied to the first diode.

6. A sensor as claimed in claim 1, wherein during the sensing mode a buffered sensing signal with a DC offset greater than the sensing signal is applied to the second diode.

7. A sensor as claimed in claim 1, further comprising a reference circuit for measuring the affects of temperature on the sensing signal due to the characteristics of the first and second diodes and outputting a reference sensing measurement that can be used to adjust the sensing signal.

8. A sensor as claimed in claim 7, wherein the reference circuit further comprises:

a set of reverse biased diodes positioned in close proximity to the first diode and the second diode; and

a reference capacitor coupled to the set of reverse biased diodes.

9. A sensor as claimed in claim 1, wherein the first transistor and second transistor are field effect transistors (FETs).

10. A method for sensing an occupant in a seat comprising:

providing a sensor/heat pad for outputting a sensing signal;

coupling a first diode to a first node of the sensor/heat pad;

coupling a second diode to a second node of the sensor/heat pad;

coupling a first transistor to the first diode;

coupling a second transistor to the second diode; and

during a sensing mode, opening the first and second transistors and applying a reverse-biased signal to the first diode and the second diode so that the sensor/heat pad is isolated from the first and second transistor.

11. A method for sensing an occupant in a seat as claimed in claim 10, further comprising:

coupling a power source to the first transistor; and

coupling the second transistor to ground.

12. A method for sensing an occupant in a seat as claimed in claim 11, comprising:

during a heating mode, closing the first and second transistors; and

enabling the power source so that a current flows from the power source to ground.

13. A method for sensing an occupant in a seat as claimed in claim 10, further comprising:

providing a reference circuit for measuring the affects of temperature on the sensing signal due to the characteristics of the first and second diodes; and

outputting a reference sensing measurement that can be used to adjust the sensing signal.

14. An occupant sensor for sensing an occupant in a seat, comprising:

a sensor/heat pad for outputting a sensing signal;

a first diode coupled to a first node of the sensor/heat pad;

a second diode coupled to a second node of the sensor/heat pad;

a first transistor coupled to the first diode; and

a second transistor coupled to the second diode, wherein during a sensing mode, the first and second transistors are opened and a reverse-biased signal is applied to the first diode and the second diode so that the sensor/heat pad is isolated from the first and second transistors.

15. A sensor, comprising:

a conductor used to sense at high frequencies and conduct current at low frequencies;

a first diode coupled to a first node of the conductor;

a second diode coupled to a second node of the conductor;

a first transistor coupled to the first diode; and

a second transistor coupled to the second diode, wherein during a sensing mode, the first and second transistors are opened and a driven shield signal is applied to the first diode and the second diode so that the conductor is isolated from the first and second transistors.

16. A sensor as claimed in claim 15, further comprising:

a power source coupled to the first transistor and wherein the second transistor is coupled to ground.

17. A sensor as claimed in claim 16, wherein during a heating mode, the first and second transistors are closed and a current flows from the power source to ground.

18. A sensor as claimed in claim 15, wherein the sensing signal is sinusoidal.

19. A sensor as claimed in claim 15, wherein the conductor is a wire.

20. A sensor as claimed in claim 15, wherein during the sensing mode a buffered sensing signal with a DC offset less than the sensing signal is applied to the first diode.

21. A sensor as claimed in claim 15, wherein during the sensing mode a buffered sensing signal with a DC offset greater than the sensing signal is applied to the second diode.

22. A sensor, comprising:

a sensor/heat pad;

a first diode coupled to a first node of the sensor/heat pad;

a second diode coupled to a second node of the sensor/heat pad;

a first transistor coupled to the first diode; and

a second transistor coupled to the second diode, wherein during a sensing mode, the first and second transistors are opened and a driven shield signal is applied to the first diode and the second diode so that the sensor/heat pad is isolated from the first and second transistors.