Synchronous demodulation with precision track-and-hold circuit

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.