Self-test circuit and method for testing a microsensor

• US 20040187555A1
• Filed: 03/27/2003
• Published: 09/30/2004
• Est. Priority Date: 03/27/2003
• Status: Active Grant

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Zarabadi, Seyed R.
• Granted Patent: US 6,918,282 B2
• Time in Patent Office: Days
• US Class Current: 73/1.37
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: Y10T 29/49 Method of mechanical manufacture

Abstract

A test circuit and method provide testing of a capacitive type microsensor. The method includes applying a first signal having a first voltage potential to an input of a microsensor during a non-test operating mode. The method also includes applying a second voltage signal having a second voltage potential different than the first voltage potential during a test mode. The second voltage potential induces a net differential electrostatic force in the microsensor. The method further includes the steps of monitoring an output signal of the microsensor, comparing the output signal to an expected value when the microsensor is in the test mode, and determining if the microsensor is functioning properly as a function of the comparison.

Claims

1. A method of testing a capacitive-type microsensor, said method comprising the steps of:

applying a first signal having a first voltage potential to an input of a microsensor during a non-test operating mode;

applying a second voltage signal having a second voltage potential different than the first voltage potential during a test mode, wherein the second voltage potential induces a change in electrostatic force in the microsensor as compared to the first voltage potential and the microsensor generates an output signal;

monitoring the output signal of the microsensor;

comparing the output signal to an expected value when the microsensor is in the test mode; and

determining if the microsensor is functioning properly as a function of the comparison.

2. The method as defined in claim 1 further comprising the steps of measuring gain of the microsensor and adjusting a gain factor based on the measured gain.

3. The method as defined in claim 2, wherein the step of adjusting the gain factor comprises electronically trimming microsensor circuitry.

4. The method as defined in claim 1 further comprising the steps of:

generating the first signal as a first alternating waveform signal having high and low voltage potentials; and

generating the second signal as a second alternating waveform signal having high and low voltage potentials.

5. The method as defined in claim 4, wherein the first and second alternating wave signals comprise square wave signals.

6. The method as defined in claim 4, wherein the high and low voltage potentials of the first attenuating waveform signal are offset in voltage from the high and low voltage potentials of the second alternating waveform signal.

7. The method as defined in claim 1 further comprising the steps of receiving an input voltage from a voltage source and dividing the input voltage into the first and second voltage potentials via a resistor divider network.

8. The method as defined in claim 1 further comprising the step of setting a flag if the microsensor is determined not to be functioning properly.

9. The method as defined in claim 1, wherein the microsensor comprises variable capacitors comprising fixed capacitive plates and movable capacitive plates arranged to form a capacitive device.

10. The method as defined in claim 1, wherein the microsensor comprises a capacitive type accelerometer.

11. A test circuit for testing operation of a microsensor having a capacitive-type sensing arrangement, said test circuit comprising:

voltage selection circuitry for selecting one of a first voltage signal and a second voltage signal, wherein the second voltage signal has voltage offset from the first voltage signal;

output circuitry for applying the first voltage signal to an input to a microsensor during a non-test mode of operation, and applying the second voltage signal to the input of the microsensor during a test mode to induce a change in electrostatic force in the microsensor;

an input for receiving an output signal generated by the microsensor;

a comparator for comparing the output signal of the microsensor to an expected value during the test mode; and

a controller for determining whether the microsensor functions properly based on the comparison.

12. The test circuit as defined in claim 11, wherein the controller further measures gain of the microsensor and adjusts a gain factor based on the measured gain.

13. The test circuit as defined in claim 12 further comprising electronic trimming circuitry for adjusting the gain factor.

14. The test circuit as defined in claim 11, wherein the controller determines if the measured sensor output signal is within an acceptable range of the expected value.

15. The test circuit as defined in claim 11, wherein the controller sets a flag if the test circuit determines that the microsensor is not functioning properly.

16. The test circuit as defined in claim 11 further comprising a resistor divider network for dividing a power supply voltage into a plurality of voltage potentials including a first voltage potential of the first voltage signal and a second voltage potential of the second voltage signal.

17. The test circuit as defined in claim 11, wherein the first and second voltage signals comprise alternating wave signals.

18. The test circuit as defined in claim 17, wherein the first voltage signal comprises a first alternating signal having high and low voltage potentials and the second voltage signal comprises a second alternating signal having high and- low voltage potentials, and wherein the high and low voltage potentials of the first alternating signal are offset from the high and low voltage potentials of the second alternating circuit.

19. The test circuit as defined in claim 17, wherein the first and second alternating wave signals comprise square wave signals.

20. The test circuit as defined in claim 11, wherein the microsensor comprises a capacitive type accelerometer.