CIRCUIT AND METHOD FOR DETERMINING COMPARATOR OFFSETS OF ELECTRONIC DEVICES

• US 20120319735A1
• Filed: 06/15/2011
• Published: 12/20/2012
• Est. Priority Date: 06/15/2011
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: McQuirk, Dale J., Nagda, Miten H.
• Granted Patent: US 8,624,653 B2
• Time in Patent Office: Days
• US Class Current: 327/73
• CPC Class Codes: G01R 31/31703 Comparison aspects, e.g. signature analysis, comparators concerning scan tests G01R31/318566; concerning testers G01R31/3193

Abstract

A device includes a comparator, and a selection circuit coupled to the inputs of the comparator. The selection circuit receives reference voltages and a variable voltage. In a normal operation mode, the selection circuit provides the variable voltage and a selected reference voltage to the comparator and the comparator provides an indication based on the variable voltage. In a test mode, the selection circuit provides a first selected reference voltage and a second selected reference voltage to the comparator for determining a switching offset voltage of the comparator.

Claims

1. A method for operating a comparator, the method comprising:

in a first mode of operation, selectively providing one of a plurality of reference voltages to a first input of a first comparator, the first comparator including an output to provide an indication of a comparison of a variable voltage received at a second input of the first comparator with the selectively provided one of the plurality of reference voltages provided at the first input; and

in a second mode of operation, selectively providing a first one of the plurality of reference voltages to the first input of the first comparator and a second one of the plurality of reference voltages to the second input of the first comparator to determine a switching offset voltage of the first comparator.

2. The method of claim 1, wherein selectively providing the first one of and the second one of the plurality of reference voltages comprises:

providing successive reference voltages of the plurality of reference voltages to the first and second inputs of the first comparator to determine the first one of and the second one of the plurality of reference voltages.

3. The method of claim 2, where successively providing reference voltages comprises selectively providing the first one of the plurality of reference voltages to the second input of the first comparator and the second one of the plurality of reference voltages to the first input of the first comparator prior to selectively providing the first one of the plurality of reference voltages to the first input and the second one of the plurality of reference voltages to the second input.

4. The method of claim 1, wherein determining the switching offset voltage of the first comparator further comprises determining a voltage difference between the first reference voltage and the second reference voltage.

5. The method of claim 1, wherein during the first mode of operation, an output of the first comparator drives an input of a voltage regulator to regulate the variable voltage.

6. The method of claim 5, further comprising:

in the second mode of operation, isolating the output of the first comparator from the input of the voltage regulator.

7. The method of claim 1, further comprising:

in the second mode of operation, determining a switching offset voltage of a second comparator, wherein the determining a switching offset of the second comparator includes selectively providing the first one of the plurality of reference voltages to a first input of the second comparator and the second one of the plurality of reference voltages to a second input of the second comparator.

8. The method of claim 1, further comprising:

in the second mode of operation, determining a switching offset voltage of a second comparator, wherein the determining a switching offset of the second comparator includes selectively providing the first one of the plurality of reference voltages to a first input of the second comparator and a third one of the plurality of reference voltages to a second input of the second comparator.

9. The method of claim 1, further comprising:

in the second mode of operation, determining a switching offset of a second comparator, wherein the determining a switching offset of the second comparator includes selectively providing a third one of the plurality of reference voltages to a first input of the second comparator and a fourth one of the plurality of reference voltages to a second input of the second comparator.

10. The method of claim 1, wherein selectively providing the first reference voltage and the second reference voltage is in response to a test routine of a built-in self test processor of an integrated circuit.

11. A method for determining a switching voltage offset of a comparator, the method comprising:

providing a first reference voltage to a first input of the comparator and a second reference voltage to a second input of the comparator; and

responsive to being unable to determine the switching voltage offset of the comparator based upon the first and second reference voltages, providing the first reference voltage to the second input of the comparator and the second reference voltage to the first input of the comparator.

12. The method of claim 11, wherein providing the first reference voltage and the second reference voltage is controlled a built-in self test processor.

13. The method of claim 11, further comprising:

determining a switching offset voltage for the comparator based on a voltage difference between the first and second reference voltages.

14. The method of claim 13, further comprising:

after providing the first reference voltage to the second input of the comparator and the second reference voltage to the first input of the comparator, providing a third reference voltage to the second input of the comparator and the second reference voltage to the first input.

15. The method of claim 15, further comprising:

after providing the third reference voltage to the second input of the comparator and the second reference voltage to the first input, providing the third reference voltage to the first input of the comparator and the second reference voltage to the second input of the comparator.

16. A device comprising:

a comparator comprising a first input, a second input, and an output;

a selection circuit, including a first output coupled to the first input and a second output coupled to the second input, the selection circuit including a first plurality of inputs, each of the first plurality of inputs coupled to a receive a reference voltage of a corresponding plurality of reference voltages, the selection circuit including a third input coupled to receive a variable voltage, wherein during a first mode of operation, the selection circuit provides the variable voltage to the first input and provides a selected voltage of the plurality of voltages to the second input, wherein the comparator provides at its output an indication of a comparison of the variable voltage and the selected voltage;

wherein during a second mode of operation, the selection circuit provides a first selected voltage of the plurality of reference voltages to the first input and a second selected voltage of the plurality of reference voltages to the second input for determining a switching offset voltage of the comparator.

17. The device of claim 16, wherein during the second mode of operation, the selection circuit selectively couples different inputs of the first plurality of inputs to the first input to provide different reference voltages prior to providing the first selected voltage to the first input and the second selected voltage to the second input.

18. The device of claim 16, wherein during the second mode of operation, the selection circuit selectively provides the first selected voltage to the second input and the second selected voltage to the first input, prior to providing the first selected voltage to the first input and the second selected voltage to the second input.

19. The device of claim 16, wherein the selection circuit determines the switching offset voltage as a voltage difference between the first selected voltage and the second selected voltage.

20. The device of claim 16, wherein:

during the first mode of operation, the output drives an input of a voltage regulator to regulate the variable voltage; and

the device further comprising a switch coupled to the output of the comparator to isolate the output of the comparator the input of the voltage regulator, wherein the switch is open during the second mode.