CIRCUIT AND METHOD FOR PRESSURE SENSOR TESTING

• US 20110023577A1
• Filed: 07/31/2009
• Published: 02/03/2011
• Est. Priority Date: 07/31/2009
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Dawson, Chad S.
• Granted Patent: US 8,245,562 B2
• Time in Patent Office: Days
• US Class Current: 73/1.57
• CPC Class Codes: G01L 27/007 Malfunction diagnosis, i.e. diagnosing a sensor defect

Abstract

A method for testing a pressure sensor having a first node and a second node includes coupling the first node to a first input of an amplifier and coupling a reference voltage to a second input of the amplifier; applying a transfer function to an output of the amplifier to provide a first output voltage that is based on a difference in voltage between the first node and the reference voltage; coupling the reference voltage to the first input and coupling the second node to the second input; obtaining a second output voltage at the output of the amplifier; and determining, based on the first and second output voltages, whether the pressure sensor passed or failed. During normal operation, the first node is coupled to the first input and the second node to the second input, and a second transfer function is applied to the output of the amplifier.

Claims

1. A method for testing a pressure sensor having a first node and a second node, the method comprising:

coupling the first node to a first input of an amplifier and coupling a reference voltage to a second input of the amplifier;

applying a transfer function to an output of the amplifier to provide a first output voltage that is based on a difference in voltage between the first node and the reference voltage;

coupling the reference voltage to the first input of the amplifier and coupling the second node to the second input of the amplifier;

obtaining a second output voltage at the output of the amplifier; and

determining, based on the first output voltage and the second output voltage, whether the pressure sensor passed or failed.

2. The method of claim 1, wherein the step of determining comprises:

comparing the first output voltage with the second output voltage to determine whether the pressure sensor passed or failed.

3. The method of claim 1, wherein the step of determining comprises:

determining an error between the first output voltage and the second output voltage; and

determining whether the pressure sensor passed or failed based on the error.

4. The method of claim 1, wherein, during normal operation, the method further comprises:

coupling the first node to a first input of an amplifier and the second node to a second input of the amplifier; and

applying a second transfer function to the output of the amplifier to provide a third output voltage that is based on a difference in voltage between the first node and the second node of the pressure sensor.

5. The method of claim 1, further comprising:

characterizing the first node of the pressure sensor by coupling the first node to the first input of an amplifier and coupling the reference voltage to a second input of the amplifier and obtaining a first plurality of data points under different conditions;

characterizing the second node of the pressure sensor by coupling the reference voltage to the first input of the amplifier and coupling the second node to the second input of the amplifier and obtaining a second plurality of data points under different conditions;

determining the transfer function based on the first and second plurality of data points; and

storing the transfer function.

6. The method of claim 1, wherein the steps of coupling the first node, applying, coupling the reference voltage, obtaining, and determining are performed in response to a signal which indicates entry into a test mode of the pressure sensor.

7. A method for testing a pressure sensor having a first node and a second node, the method comprising:

during normal operation, coupling the first node to a first input of an amplifier, the second node to a second input of the amplifier and applying a first transfer function to an output of the amplifier to provide a first output voltage that is based on a difference in voltage between the first node and the second node of the pressure sensor; and

during a test mode;

coupling the first node to the first input of the amplifier and coupling a reference voltage to the second input of the amplifier;

applying a second transfer function to the output of the amplifier to provide a second output voltage that is based on a difference in voltage between the first node and the reference voltage;

coupling the reference voltage to the first input of the amplifier and coupling the second node to the second input of the amplifier;

obtaining a third output voltage at the output of the amplifier;

determining an error between the second output voltage and the third output voltage; and

determining whether the pressure sensor passed or failed based on the error.

8. The method of claim 7, further comprising:

receiving a test mode indicator to indicate when to enter the test mode.

9. The method of claim 7, further comprising:

characterizing the first node of the pressure sensor by coupling the first node to the first input of an amplifier and coupling the reference voltage to a second input of the amplifier and obtaining a first plurality of data points under different conditions;

characterizing the second node of the pressure sensor by coupling the reference voltage to the first input of the amplifier and coupling the second node to the second input of the amplifier and obtaining a second plurality of data points under different conditions;

determining the second transfer function based on the first and second plurality of data points; and

storing the second transfer function.

10. The method of claim 9, further comprising:

characterizing the pressure sensor by coupling the first node to the first input of an amplifier and coupling the second node to the second input of the amplifier and obtaining a third plurality of data points under different conditions;

determining the first transfer function based on the third plurality of data points; and

storing the first transfer function.

11. A pressure sensing circuit comprising:

a pressure sensor having a first node and a second node;

an amplifier having a first input, a second input, and an output;

transfer function circuitry coupled to the output of the amplifier, wherein the transfer function circuitry applies a first transfer function to the output of the amplifier to provide a first output voltage;

control circuitry which, in response to a test mode indicator indicating entry into test mode;

causes the first node of the pressure sensor to be coupled to the first input of the amplifier, a reference voltage to be coupled to the second input of the amplifier during, and the transfer function circuitry to apply the first transfer function to provide the first output voltage, and

causes the reference voltage to be coupled to the first input of the amplifier and the second node of the pressure sensor to be coupled to the second input of the amplifier, wherein the output of the amplifier provides a second output voltage; and

error detection circuitry, which, in response to the test mode indicator indicating entry into test mode, determines an error between the first output voltage and the second output voltage, and, based on the error, provides a pass/fail indicator which indicates whether the pressure sensor passes or fails.

12. The pressure sensing circuit of claim 11, wherein the transfer function circuitry applies a second transfer function to the output of the amplifier to provide a third output voltage.

13. The pressure sensing circuit of claim 12, wherein the control circuitry, in response to the test mode indicator indicating normal operation, causes the first node of the pressure sensor to be coupled to the first input of the amplifier, the second node of the pressure sensor to be coupled to the second input of the amplifier, and the transfer function circuitry to apply the second transfer function to provide the third output voltage.

14. The pressure sensing circuit of claim 12, further comprising:

storage circuitry coupled to the transfer function circuitry and the control circuitry which stores coefficients of the first transfer function and coefficients of the second transfer function.

15. The pressure sensing circuit of claim 14, wherein the coefficients of the first transfer function and the coefficients of the second transfer function are determined and stored into the storage circuitry during manufacture of the pressure sensing circuit.

16. The pressure sensing circuit of claim 11, further comprising:

storage circuitry coupled to the transfer function circuitry and the control circuitry which stores coefficients of the first transfer function.

17. The pressure sensing circuit of claim 11, further comprising:

a first switch having a first terminal coupled to the first node, a second terminal coupled to a reference voltage, and a third terminal coupled to the first input of the amplifier, wherein the first switch, in response to a first switch control signal, either couples the first terminal to the third terminal or the second terminal to the third terminal; and

a second switch having a first terminal coupled to the second node, a second terminal coupled to the reference voltage, and a third terminal coupled to the second input of the amplifier, wherein the second switch, in response to a second switch control signal, either couples the first terminal to the third terminal or the second terminal to the third terminal.

18. The pressure sensing circuit of claim 17, wherein the control circuitry generates each of the first and second switch control signals in response to the test mode indicator.

19. The pressure sensing circuit of claim 11, wherein the pressure sensor comprises a wheatstone bridge.

20. The pressure sensing circuit of claim 19, wherein the wheatstone bridge comprises a first piezoelectric device coupled between a first voltage supply and the first node, a second piezoelectric device coupled between the first voltage supply and the second node, a third piezoelectric device coupled between the second node and a second voltage supply, and a fourth piezoelectric device coupled between the first node and the second voltage supply.