Methods for calibrating over-the-air path loss in over-the-air radio-frequency test systems

• US 8,660,812 B2
• Filed: 02/25/2011
• Issued: 02/25/2014
• Est. Priority Date: 06/04/2010
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Gregg, Justin, Takeya, Tomoki, Donovan, David A.
• Primary Examiner(s): Breene, John E
• Assistant Examiner(s): Zhang, Ruihua
• Application Number:
  US13/035,026
• Publication Number:
  US 20120221277A1
• Time in Patent Office: 1,096 Days
• Field of Search: 702/106, 455/67.11, 455/67.12, 455/115.1, 455/226.1, 340/7.41, 340/7.44
• US Class Current: 702/106
• CPC Class Codes: H04B 17/104 of other parameters, e.g. DC offset, delay or propagation times
• CPC Class Codes: H04B 17/11 for calibration
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 17/318 Received signal strength

Abstract

Calibration equipment for calibrating multiple test stations in a test system is provided. Each test station may include a test unit, a test chamber with an over-the-air antenna, and a radio-frequency (RF) cable that connects the test unit to the test chamber. Reference devices under test (DUTs) may be used to calibrate uplink and downlink path loss (e.g., OTA path loss, RF cable path loss, and variations of the test unit) associated with each test station. The reference DUTs may calibrate each test station at desired frequencies to generate a path loss table. Once calibrated, the test chambers may be used during production testing to test factory DUTs. During production testing, the transmit/receive power efficiency of each factory DUT may be calculated based on values in the path loss table to determine whether a particular production DUT is a passing or failing DUT according to pass/fail criteria.

Claims

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

calibrating a master test chamber that is different than the test chamber using a golden reference device under test that includes storage circuitry and that is placed within the master test chamber;

calibrating the reference device under test in the calibrated master test chamber to obtain a reference offset; and

with the reference device under test, calibrating the test chamber by computing a path loss based on the reference offset.

2. The method defined in claim 1, wherein computing the path loss based on the reference offset comprises computing an uplink path loss for the test chamber.

3. The method defined in claim 1, wherein computing the path loss based on the reference offset comprises computing a downlink path loss for the test chamber.

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

storing the reference offset in the reference device under test; and

with a test host, retrieving the reference offset from the reference device under test to compute the path loss.

5. The method defined in claim 1, wherein the test station is connected to computing equipment, the method further comprising:

storing the reference offset on a database that is stored on the computing equipment; and

with a test host, retrieving the reference offset from the database to compute the path loss.

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

with the test station, testing a plurality of production devices under test.

7. The method defined in claim 1, wherein the path loss comprises an over-the-air path loss and wherein calibrating the master test chamber with the golden reference device under test comprises measuring an over-the-air path loss value associated with the master test chamber.

8. A method for performing over-the-air wireless testing on a factory device under test with a test station, wherein the test station includes a test chamber having an over-the-air antenna, a test unit, and a radio-frequency cable that connects the over-the-air antenna to the test unit, wherein the test station is connected to computing equipment, and wherein the computing equipment stores a path loss table, the method comprising:

with a plurality of reference devices under test, calibrating the test station;

with the test host, computing path loss values for the path loss table based on measurements taken from the plurality of reference devices under test;

directing the factory device under test to transmit radio-frequency signals to the over-the-air antenna;

with the test unit, measuring a test unit power level while the factory device under test is transmitting the radio-frequency signals to the over-the-air antenna; and

with a test host, computing a transmit power level for the factory device under test based on the test unit power level and an average uplink path loss value computed using measured uplink path loss values in the path loss table.

9. The method defined in claim 8, further comprising:

with the test unit, transmitting radio-frequency signals through the over-the-air antenna to the factory device under test;

in response to the radio-frequency signals transmitted from the test unit, transmitting wireless information to the test unit with the factory device under test; and

with the test host, computing a receive power level for the factory device under test based on the wireless information and an average downlink path loss value computed using measured downlink path loss values in the path loss table.

10. The method defined in claim 9, wherein transmitting the wireless information to the test unit with the factory device under test comprises transmitting a received signal strength indicator to the test unit with the factory device under test.

11. The method defined in claim 8, wherein each reference device under test has a respective reference offset and wherein computing the path loss values for the path loss table based on the measurements taken from the plurality of reference devices under test comprises computing uplink and downlink path loss values while taking into account the reference offset of each reference device under test.

12. The method defined in claim 11, further comprising:

calibrating each of the plurality of reference devices under test in a master test chamber to determine their respective reference offset.

13. A method of calibrating a test station with a plurality of reference devices, wherein the test station includes a slave 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 golden reference device that includes storage circuitry, calibrating a master test chamber by taking wireless signal measurements in the master test chamber;

calibrating the plurality of reference devices in the master test chamber; and

with the plurality of reference devices, calibrating the slave test chamber by computing a slave test chamber path loss.

14. The method defined in claim 13, wherein calibrating the plurality of reference devices in the master test chamber comprises computing reference offset values for each of the plurality of reference devices.

15. The method defined in claim 14, wherein calibrating the slave test chamber comprises computing an average uplink path loss based on the reference offset values.

16. The method defined in claim 14, wherein calibrating the slave test chamber comprises computing an average downlink path loss based on the reference offset values.

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

testing a plurality of factory devices in the slave test chamber.

18. The method defined in claim 13, further comprising, wherein calibrating the master test chamber comprises making over-the-air path loss measurements using an antenna in the golden reference device.