Synchronous demodulation with precision track-and-hold circuit

• US 20060097780A1
• Filed: 11/11/2004
• Published: 05/11/2006
• Est. Priority Date: 11/11/2004
• Status: Active Grant

• Current Assignee: Delphi Technologies Ip Limited (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Griffin, Dennis P., Fultz, William W., Noland, George J.
• Granted Patent: US 7,384,066 B2
• Time in Patent Office: Days
• US Class Current: 329/313
• CPC Class Codes: B60R 21/01512 Passenger detection systems
• CPC Class Codes: G01R 19/04 Measuring peak values or amplitude or envelope of ac or of pulses

Abstract

A synchronous demodulation circuit uses a digitally controlled track-and-hold circuit to capture the peak amplitude of a rectified signal. A microcontroller controls the track-and-hold circuit. In particular, the microcontroller controls a hold mode of the track-and-hold circuit to capture the peak amplitude of the rectified signal.

Claims

1. A synchronous demodulation circuit arrangement comprising:

a sensor interface circuit coupled to receive a sensor signal, the sensor interface circuit associated with a propagation delay;

a microcontroller configured to generate a microcontroller timing signal and to adjust timing of the microcontroller timing signal as a function of the propagation delay; and

a track-and-hold circuit arrangement coupled to receive the sensor signal and responsive to the microcontroller timing signal, the track-and-hold circuit arrangement configured to periodically sample the sensor signal;

wherein the microcontroller is configured to detect a peak amplitude of the sensor signal and generate a hold control signal in response to the detected peak amplitude and the track-and-hold circuit arrangement is configured to output a peak indication signal in response to the hold control signal.

2. The synchronous demodulation circuit arrangement of claim 1, wherein the sensor interface circuit is configured to process the sensor signal before the sensor signal is sampled by the track-and-hold circuit arrangement.

3. The synchronous demodulation circuit arrangement of claim 1, wherein the sensor interface circuit comprises at least one of a rectifier arrangement, an amplifier, and a bandpass filter.

4. The synchronous demodulation circuit arrangement of claim 1, wherein the track-and-hold circuit arrangement comprises a plurality of switches.

5. The synchronous demodulation circuit arrangement of claim 4, wherein the switches comprise MOSFET analog switches.

6. The synchronous demodulation circuit arrangement of claim 4, wherein the track-and-hold circuit arrangement further comprises a hold capacitor.

7. The synchronous demodulation circuit arrangement of claim 1, wherein the microcontroller is configured to

command the track-and-hold circuit to sample a sensor drive clock signal at predetermined time intervals;

detect a peak amplitude of the sensor drive clock signal; and

adjust timing of the microcontroller timing signal in response to detecting the peak amplitude of the sensor drive clock signal.

8. The synchronous demodulation circuit arrangement of claim 1, wherein the microcontroller comprises a memory configured to store data for adjusting the timing of the microcontroller timing signal.

9. An occupant detection system comprising:

a sensor configured to generate a sensor signal in response to sensing a vehicle occupant;

a sensor interface circuit coupled to receive the sensor signal, the sensor interface circuit associated with a propagation delay;

a microcontroller configured to generate a microcontroller timing signal and to adjust timing of the microcontroller timing signal as a function of the propagation delay; and

a track-and-hold circuit arrangement coupled to receive the sensor signal and responsive to the microcontroller timing signal, the track-and-hold circuit arrangement configured to periodically sample the sensor signal;

wherein the microcontroller is configured to detect a peak amplitude of the sensor signal and generate a hold control signal in response to the detected peak amplitude and the track-and-hold circuit arrangement is configured to output a peak indication signal in response to the hold control signal.

10. The occupant detection system of claim 9, wherein the sensor interface circuit is configured to process the sensor signal before the sensor signal is sampled by the track-and-hold circuit arrangement.

11. The occupant detection system of claim 9, wherein the sensor interface circuit comprises at least one of a rectifier arrangement, an amplifier, and a bandpass filter.

12. The occupant detection system of claim 9, wherein the track-and-hold circuit arrangement comprises a plurality of MOSFET analog switches.

13. The occupant detection system of claim 12, wherein the track-and-hold circuit arrangement further comprises a hold capacitor.

14. The occupant detection system of claim 9, wherein the microcontroller is configured to:

command the track-and-hold circuit to sample a sensor drive clock signal at predetermined time intervals;

detect a peak amplitude of the sensor drive clock signal; and

adjust timing of the microcontroller timing signal in response to detecting the peak amplitude of the sensor drive clock signal.

15. The occupant detection system of claim 9, wherein the microcontroller comprises a memory configured to store data for adjusting the timing of the microcontroller timing signal.

16. The occupant detection system of claim 9, wherein the sensor signal comprises an alternating current signal.

17. The occupant detection system of claim 9, wherein the sensor comprises at least one of an infrared sensor and a linear variable differential transformer.

18. A method to demodulate a signal received via an interface circuit, the method comprising:

synchronizing a microcontroller to a drive signal at least in part by detecting an edge of the drive signal;

adjusting a microcontroller timing signal as a function of a propagation delay of the interface circuit;

detecting a peak amplitude of the signal received via the interface circuit;

in response to detecting the peak amplitude, generating a hold control signal as a function of the adjusted microcontroller timing signal; and

generating a peak indication signal in response to the hold control signal.

19. The method of claim 18, wherein the hold control signal is generated while an amplitude of the signal received via the interface circuit is within 1% of the peak amplitude.

20. The method of claim 18, further comprising compensating for an offset voltage.

21. The method of claim 18, further comprising:

sampling a drive clock signal at predetermined time intervals;

detecting a peak amplitude of the drive clock signal; and

adjusting the microcontroller timing signal in response to detecting the peak amplitude of the drive clock signal.

22. A method to detect a vehicle occupant, the method comprising:

generating a sensor signal in response to sensing a vehicle occupant;

providing the sensor signal to a demodulation circuit arrangement via an interface circuit;

synchronizing a microcontroller to a sensor drive signal at least in part by detecting an edge of the sensor drive signal;

adjusting a microcontroller timing signal as a function of a propagation delay of the interface circuit;

detecting a peak amplitude of the sensor signal;

in response to detecting the peak amplitude, generating a hold control signal as a function of the adjusted microcontroller timing signal; and

generating a peak indication signal in response to the hold control signal.

23. The method of claim 22, wherein the hold control signal is generated while an amplitude of the sensor signal is within 1% of the peak amplitude of the sensor signal.

24. The method of claim 22, further comprising compensating for an offset voltage.

25. The method of claim 22, further comprising:

sampling a sensor drive clock signal at predetermined time intervals;

detecting a peak amplitude of the sensor drive clock signal; and

adjusting the microcontroller timing signal in response to detecting the peak amplitude of the sensor drive clock signal.

26. The method of claim 22, wherein the sensor signal comprises an alternating current signal.

27. The method of claim 22, wherein the sensor signal is generated by an infrared sensor.

28. The method of claim 22, wherein the sensor signal is generated by a sensor comprising a linear variable differential transformer.

29. A microcontroller-readable medium having microcontroller-executable instructions that, when executed by a microcontroller, cause the microcontroller to:

synchronize the microcontroller to a drive signal at least in part by detecting an edge of the drive signal;

adjust a microcontroller timing signal as a function of a propagation delay of an interface circuit;

detect a peak amplitude of a signal received via the interface circuit; and

in response to detecting the peak amplitude, generate a hold control signal as a function of the adjusted microcontroller timing signal.

30. The microcontroller-readable medium of claim 29, wherein the hold control signal is generated while an amplitude of the signal received via the interface circuit is within 1% of the peak amplitude.

31. The microcontroller-readable medium of claim 29, further having microcontroller-executable instructions that, when executed by the microcontroller, cause the microcontroller to generate a null control signal.

32. The microcontroller-readable medium of claim 29, further having microcontroller-executable instructions that, when executed by the microcontroller, cause the microcontroller to:

sample a drive clock signal at predetermined time intervals;

detect a peak amplitude of the drive clock signal; and

adjust the microcontroller timing signal in response to detecting the peak amplitude of the drive clock signal.