Self test of MEMS accelerometer with ASICS integrated capacitors

• US 9,488,693 B2
• Filed: 01/16/2013
• Issued: 11/08/2016
• Est. Priority Date: 04/04/2012
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Semiconductor Corporation (ON Semiconductor Corporation)
• Inventors: Kleks, Jonathan Adam, Opris, Ion, Seng, Justin
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): RHODES-VIVOUR, TEMILADE S
• Application Number:
  US13/742,994
• Publication Number:
  US 20130265070A1
• Time in Patent Office: 1,392 Days
• Field of Search: 324/750.3
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 7/008 MEMS characterised by an electronic circuit specially adapted for controlling or driving the same B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0868 using self-test structures integrated into the microstructure
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 31/3187 Built-in tests
• CPC Class Codes: G06F 2101/00 Indexing scheme relating to the type of digital function generated
• CPC Class Codes: H01L 21/00 Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
• CPC Class Codes: H01L 2223/00 Details relating to semiconductor or other solid state devices covered by the group H01L23/00

Abstract

An apparatus comprises a micro-electromechanical system (MEMS) sensor including a first capacitive element and a second capacitive element and an integrated circuit (IC). The IC includes a switch network circuit and a capacitance measurement circuit. The switch network circuit is configured to electrically decouple the first capacitive element of the MEMS sensor from a first input of the IC and electrically couple the second capacitive element to a second input of the IC. The capacitance measurement circuit can be configured to measure capacitance of the second capacitive element of the MEMS sensor during application of a first electrical signal to the decoupled first capacitive element.

Claims

1. An apparatus comprising:

a micro-electromechanical system (MEMS) sensor including a first MEMS capacitive element and a second MEMS capacitive element; and

an integrated circuit (IC), including;

a switch network circuit configured to electrically decouple the first MEMS capacitive element of the MEMS sensor from a first input of the IC and electrically couple the second MEMS capacitive element to a second input of the IC; and

a capacitance measurement circuit configured to measure capacitance of the second MEMS capacitive element of the MEMS sensor during application of a first electrical signal to the decoupled first capacitive element; and

a test circuit configured to apply a first square wave signal to the first decoupled MEMS capacitive element and apply a second square wave signal to an external circuit node common to the first MEMS capacitive element and the second MEN S capacitive element,

wherein the capacitance measurement circuit is configured to measure the capacitance of the second MEMS capacitive element during application of the first and second square wave signals.

2. The apparatus of claim 1,

wherein the switch network is configured to electrically decouple the second MEMS capacitive element of the MEMS sensor from the IC and electrically couple the first MEMS capacitive element to the IC, and

wherein the capacitance measurement circuit is configured to measure capacitance of the first MEMS capacitive element of the MEMS sensor during application of a second electrical signal to the decoupled second MEMS capacitive element.

3. The apparatus of claim 1,

wherein the second square wave signal has a phase opposite a phase of the first square wave signal.

4. The apparatus of claim 1,

wherein the second square wave signal is in phase with the first square wave signal, and.

5. The apparatus of claim 1, wherein the capacitance measurement circuit includes a differential input analog to digital converter (ADC) circuit configured to produce a digital value representative of capacitance of the second MEMS capacitive element.

6. The apparatus of claim 5,

wherein the IC includes a self test capacitor pair,

wherein the switch network circuit is configured to:

electrically couple the second MEMS capacitive element of the MEMS sensor to a first input of the ADC circuit; and

configure the self test capacitor pair as a capacitance-to-voltage sensor internal to the IC and electrically couple the self test capacitor pair to a second input of the ADC circuit.

7. The apparatus of claim 5,

wherein the IC includes at least one offset capacitor configured to cancel any common mode offset of the ADC circuit;

wherein the switch network circuit is configured to electrically couple the second MEMS capacitive element and the offset capacitor to the first input of the differential input ADC circuit during measurement of the second MEMS capacitive element.

8. The apparatus of claim 5, wherein the ADC circuit is a differential input sigma-delta ADC circuit.

9. The apparatus of claim 1,

wherein the switch network circuit is configured to operate in a test mode and in a normal mode,

wherein in the test mode the switch network is configured to electrically decouple at least one of the first MEMS capacitive element or the second MEMS capacitive from the IC,

wherein in the normal mode the switch network circuit is configured to couple the first and second MEMS capacitive elements of the MEMS sensor as a first capacitive element pair, and

wherein the first capacitive element pair is configured to change capacitance in response to acceleration in a first direction.

10. The apparatus of claim 1, wherein the IC includes a capacitance-to-voltage sensor circuit.

11. The apparatus of claim 1, wherein the MEMS sensor includes an accelerometer.

12. A method comprising:

electrically decoupling a first MEMS capacitive element of an MEMS sensor from an IC;

applying a first electrical signal to the decoupled MEMS capacitive element; and

measuring capacitance of a second MEMS capacitive element of the MEMS sensor during application of the first electrical signal,

wherein the first and second MEMS capacitive elements are measured during a test mode,

wherein, in a normal operating mode, the first and second MEMS capacitive elements comprise a first capacitive element pair and are configured to change capacitance in response to acceleration in a first direction,

wherein, in the normal operating mode, any common mode voltage is canceled using at least one offset capacitor, and

wherein, during the test mode, the offset capacitor and the second MEMS capacitive element are electrically coupled to the first input of the differential input ADC circuit during measurement of the second MEMS capacitive element.

13. The method of claim 12, including:

electrically decoupling the second MEMS capacitive element of the MEMS sensor from the IC;

applying a second electrical signal to the second capacitive element; and

measuring capacitance of the first capacitive element of the MEMS sensor during application of the second electrical signal.

14. The method of claim 13,

wherein applying a first electrical signal includes applying a first square wave signal to the first MEMS capacitive element,

wherein measuring capacitance of the second MEMS capacitive element includes applying a second square wave signal to an external node common to the first MEMS capacitive element and the second MEMS capacitive element,

wherein capacitance of the second MEMS capacitive element is measured during application of the first and second square wave signals, and

wherein the second square wave signal has a phase opposite a phase of the first square wave signal.

15. The method of claim 13,

wherein applying a first electrical signal includes applying a first square wave signal to the first MEMS capacitive element,

wherein measuring capacitance of the second MEMS capacitive element includes applying a second square wave signal to an external node common to the first MEMS capacitive element and the second MEMS capacitive element,

wherein capacitance of the second MEMS capacitive element is measured during application of the first and second square wave signals, and

wherein the second square wave signal is in phase with the first square wave signal.

16. The method of claim 12, wherein measuring capacitance of the second MEMS capacitive element includes producing a digital value representative of capacitance of the second MEMS capacitive element using a differential input sigma-delta analog-to-digital converter (ADC) circuit.

17. The method of claim 12, wherein measuring the capacitance of the second MEMS capacitive element includes:

electrically coupling the second MEMS capacitive element to a first input of a differential input ADC circuit; and

electrically coupling a self test capacitor pair, internal to the IC, to a second input of the ADC circuit, wherein the self test capacitor pair forms a charge-to-voltage sensor internal to the IC.

18. The method of claim 12, wherein measuring capacitance of a second MEMS capacitive element of the MEMS sensor includes measuring capacitance of a second MEMS capacitive element of an acceleration-to-capacitance MEMS sensor.