Detecting sensitivity faults in capacitive sensors by using pull-in functionality

Patent metadata

Field	Value
Publication number	US-11927645-B2
Application number	US-202117463753-A
Country	US
Kind code	B2
Filing date	Sep 1, 2021
Priority date	Sep 1, 2021
Publication date	Mar 12, 2024
Grant date	Mar 12, 2024

Abstract

A capacitive sensor includes a first electrode structure; a second electrode structure that is counter to the first electrode structure, wherein the second electrode structure is movable relative to the first electrode structure and is capacitively coupled to the first electrode structure to form a capacitor having a capacitance that changes with a change in a distance between the first electrode structure and second electrode structure; a signal generator configured to apply an electrical signal at an input or at an output of the capacitor to induce a voltage transient response at the output of capacitor; and a diagnostic circuit configured to detect a fault in the capacitive sensor by measuring a time constant of the first voltage transient response and detecting the fault based on the time constant and based on whether the first electrical signal is the pull-in signal or the non-pull-in signal.

First claim

What is claimed is:

1. A capacitive sensor, comprising:
a first electrode structure;
a second electrode structure that is counter to the first electrode structure, wherein the second electrode structure is movable relative to the first electrode structure in response to an external force acting thereon, wherein the second electrode structure is capacitively coupled to the first electrode structure to form a first capacitor having a first capacitance that changes with a change in a distance between the first electrode structure and second electrode structure, wherein the first capacitance is representative of the external force,
wherein a pull-in event occurs when the first electrode structure is in direct contact with the second electrode structure causing the first capacitance to be equal to or greater than a pull-in capacitance and a non-pull-in event occurs when the first electrode structure is not in direct contact with the second electrode structure causing the first capacitance to be less than the pull-in capacitance;
a signal generator configured to apply a first electrical signal at an input or at an output of the first capacitor to induce a first voltage transient response at the output of first capacitor, wherein the first electrical signal is a pull-in signal configured to induce a pull-in event in the absence of a fault or a non-pull-in signal configured induce a non-pull-in event in the absence of a fault; and
a diagnostic circuit configured to detect a fault in the capacitive sensor by measuring a first time constant of the first voltage transient response and detecting the fault based on the first time constant and based on whether the first electrical signal is the pull-in signal or the non-pull-in signal.

2. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit is configured to compare the first time constant to a pull-in threshold value that corresponds to the pull-in capacitance,
when the first electrical signal is a pull-in signal, the diagnostic circuit is configured to detect a first fault on a first condition that the first time constant is less than the pull-in threshold value, and
when the first electrical signal is a non-pull-in signal, the diagnostic circuit is configured to detect a second fault on a second condition that the first time constant is equal to or greater than the pull-in threshold value.

3. The capacitive sensor of claim 1 , wherein:
the pull-in event causes the first capacitance to be at a maximum capacitance and a non-pull-in event causes the first capacitance to be less than the maximum capacitance,
the diagnostic circuit is configured to determine whether the first time constant corresponds to the maximum capacitance,
when the first electrical signal is a pull-in signal, the diagnostic circuit is configured to detect a first fault on a first condition that the first time constant does not correspond to the maximum capacitance, and
when the first electrical signal is a non-pull-in signal, the diagnostic circuit is configured to detect a second fault on a second condition that the first time constant corresponds to the maximum capacitance.

4. The capacitive sensor of claim 1 , wherein:
the first electrical signal, as the pull-in signal, includes a first signal step from a non-pull-in value to a pull-in value,
the first electrical signal, as the non-pull-in signal, includes a second signal step from the pull-in value to the non-pull-in value, and
the pull-in value is configured to induce the pull-in event in the absence of a fault and the non-pull-in value is configured to induce the non-pull-in event in the absence of a fault.

5. The capacitive sensor of claim 1 , wherein the first electrode structure comprises a first conductive structure and an insulating layer arranged on a surface of the first conductive structure that faces the second electrode structure, and
the second electrode structure comprises a second conductive structure.

6. The capacitive sensor of claim 1 , wherein the second electrode structure comprises a first conductive structure and an insulating layer arranged on a surface of the first conductive structure that faces the first electrode structure, and
the first electrode structure comprises a second conductive structure.

7. The capacitive sensor of claim 1 , wherein the first electrical signal causes the first capacitor to charge to a maximum voltage or to discharge to a minimum voltage.

8. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit comprises a comparator, a counter, and a fault detector,
the comparator is configured to receive an output voltage representative of the first voltage transient response and compare the output voltage to a reference threshold in order to generate a comparison result having one of two comparator values,
the counter is configured to stop counting when the comparison result changes from a first comparator value to a second comparator value and output a stopped counter value representative of the first time constant,
the fault detector is configured to compare the stopped counter value to a pull-in threshold value that corresponds to the pull-in capacitance,
when the first electrical signal is a pull-in signal, the fault detector is configured to generate a first error signal in response to the stopped counter value being less than the pull-in threshold value, and
when the first electrical signal is a non-pull-in signal, the fault detector is configured to generate a second error signal in response to the stopped counter value being equal to or greater than the pull-in threshold value.

9. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit comprises a comparator and a fault detector,
the comparator is configured to receive an output voltage representative of the first voltage transient response, and compare the output voltage to a reference threshold in order to detect the first time constant, and
the fault detector is configured to compare the first time constant to a pull-in threshold value that corresponds to the pull-in capacitance,
when the first electrical signal is a pull-in signal, the fault detector is configured to generate a first error signal in response to the first time constant being less than the pull-in threshold value, and
when the first electrical signal is a non-pull-in signal, the fault detector is configured to generate a second error signal in response to the first time constant being equal to or greater than the pull-in threshold value.

10. The capacitive sensor of claim 9 , wherein the diagnostic circuit comprises a counter configured to output a first counter value representative of the detected first time constant and the fault detector is configured to compare the first counter value to a pull-in threshold value that corresponds to the pull-in capacitance,
when the first electrical signal is a pull-in signal, the fault detector is configured to generate a first error signal in response to the first counter value being less than the pull-in threshold value, and
when the first electrical signal is a non-pull-in signal, the fault detector is configured to generate a second error signal in response to the first counter value being equal to or greater than the pull-in threshold value.

11. The capacitive sensor of claim 1 , wherein:
the diagnostic circuit is configured to compare the first time constant to a pull-in threshold value that corresponds to the pull-in capacitance,
when the first electrical signal is a pull-in signal, the diagnostic circuit is configured to generate an error signal in response to the first time constant being less than the pull-in threshold value, and
when the first e

Assignees

• Infineon Technologies Ag

Inventors

• Stoica Dan-Ioan-Dumitru
• Buffa Cesare
• Caspani Alessandro
• Crisu Constantin
• Popescu-Stroe Victor
• Winkler Bernhard

Classifications

• G01R31/64 Primary

  Testing of capacitors · CPC title

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• G01R35/00

  Testing or calibrating of apparatus covered by the other groups of this subclass · CPC title

• G01H11/06

  by electric means · CPC title

• G01L9/12

  by making use of variations in capacitance {, i.e. electric circuits therefor} · CPC title