Methods of testing wireless devices in over-the-air radio-frequency test systems without path loss characterization

• US 8,706,044 B2
• Filed: 08/31/2010
• Issued: 04/22/2014
• Est. Priority Date: 08/31/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chang, Thomas W., Syed, Adil, Donovan, David A.
• Primary Examiner(s): Pan, Yuwen
• Assistant Examiner(s): AYOTUNDE, AYODEJI O
• Application Number:
  US12/872,963
• Publication Number:
  US 20120052816A1
• Time in Patent Office: 1,330 Days
• Field of Search: 455/67.11, 455/67.12, 455/67.14
• US Class Current: 455/67.11
• CPC Class Codes: H04W 24/06 Testing, supervising or monitoring using simulated traffic

Abstract

A method for testing wireless devices under test (DUTs) in a wireless test station is provided. Each test station may include a test unit, a test chamber with an antenna, and a radio-frequency (RF) cable that connects the test unit to the test chamber. Reference DUTs may be used to calibrate each test station to compute a corrected linear equation based on a nominal path loss value. Over-the-air (OTA) path loss of each test station may not be directly measured. Once calibrated, the test chambers may be used during product testing to test factory DUTs to determine whether a particular factory DUT satisfies pass/fail criteria. During product testing, measured output power levels may be compared with expected output power levels computed using the corrected linear equation. The amount of error between the measured and expected output power levels will determine whether a production DUT satisfies the pass/fail criteria.

Claims

1. A method of calibrating a wireless test station, wherein the wireless test station includes a test chamber having an antenna, a test unit, and a radio-frequency cable that connects the antenna to the test unit, the method comprising:

with a test host, computing a linear function, wherein the linear function provides an expected output power value as its output by receiving a requested output power value as its input;

with the test host, directing a reference device under test to produce radio-frequency signals at a first requested output power level during a first time period; and

with the test host, directing the reference device under test to produce radio-frequency signals at a second requested output power level during a second time period.

2. The method defined in claim 1, further comprising:

with the test unit, measuring a first measured output power level while the reference device under test is transmitting the radio-frequency signals at the first requested output power level during the first time period to obtain a first data point; and

with the test unit, measuring a second measured output power level while the reference device under test is transmitting the radio-frequency signals at the second requested output power level during the second time period to obtain a second data point.

3. The method defined in claim 2, further comprising:

adjusting the first and second data points based on a nominal path loss value to obtain first and second adjusted data points.

4. The method defined in claim 3, wherein a line passes through the first and second adjusted data points, the method further comprising:

with the test host, computing a given slope of the line.

5. The method defined in claim 4, further comprising:

with the test host, computing a corrected slope by calculating the reciprocal of the given slope, wherein the linear function has a slope that is equal to the corrected slope.

6. The method defined in claim 3, wherein a line passes through the first and second adjusted data points, the method further comprising:

with the test host, computing a given offset between the line and an ideal characteristic line, wherein the ideal characteristic line has a slope that is equal to one.

7. The method defined in claim 6, further comprising:

with the test host, computing a corrected offset by calculating a negative version of the given offset, wherein the linear function has an offset that is equal to the corrected offset.

8. The method defined in claim 6, wherein computing the given offset between the line that passes through the first and second adjusted data points and the ideal characteristic line comprises computing the given offset corresponding to a desired requested output power level, and wherein the desired requested output power level is equal to an average of the first requested output power level and the second requested output power level.

9. The method defined in claim 2, further comprising:

calibrating the wireless test station with additional reference devices under test to ensure accuracy of the linear function.

10. A method of calibrating test equipment for testing devices under test, comprising:

with the test equipment, configuring a reference device under test to produce signals at different requested output power levels;

with the test equipment, measuring output power levels while the reference device under test is producing the signals at the different requested output power levels; and

with the test equipment, computing a corrected linear equation based on the measured output power levels.

11. The method defined in claim 10, wherein computing the corrected linear equation takes into account a nominal path loss value.

12. The method defined in claim 10, wherein computing the corrected linear equation comprises computing a corrected slope and a corrected offset for the corrected linear equation.

13. The method defined in claim 10, further comprising:

with the test equipment, adjusting the measured output power levels based on a nominal path loss value to obtain first and second adjusted data values.

14. The method defined in claim 13, wherein a line passes through the first and second adjusted data points, the method further comprising:

with the test equipment, computing a given slope of the line.

15. The method defined in claim 14, further comprising:

with the test equipment, computing a corrected slope by calculating the reciprocal of the given slope, wherein the corrected linear equation has a slope that is equal to the corrected slope.

16. The method defined in claim 14, further comprising:

with the test equipment, computing a given offset between the line and another line with a slope of one.

17. The method defined in claim 16, further comprising:

with the test equipment, computing a corrected offset for the corrected linear equation by calculating a negative version of the given offset.

18. The method defined in claim 17, wherein computing the given offset between the line that passes through the first and second adjusted data points and the another line comprises computing the given offset corresponding to a desired requested output power level, and wherein the desired requested output power level is equal to an average of the different requested output power levels.

19. The method defined in claim 10, further comprising:

calibrating the test equipment with additional reference devices under test to ensure accuracy of the corrected linear equation.