Wireless Electronic Device With Calibrated Reflectometer

• US 20160097833A1
• Filed: 10/03/2014
• Published: 04/07/2016
• Est. Priority Date: 10/03/2014
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Han, Liang, Mow, Matthew A., Biedka, Thomas E., Pascolini, Mattia, Tsai, Ming-Ju, Judkins, James G., Lee, Victor, Schlub, Robert W.
• Granted Patent: US 9,594,147 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 29/0878 Sensors; antennas; probes; detectors wave guide measuring sections G01R1/24
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence
• CPC Class Codes: H01Q 1/243 with built-in antennas
• CPC Class Codes: H01Q 13/10 Resonant slot antennas
• CPC Class Codes: H01Q 9/42 with folded element, the folded parts being spaced apart a small fraction of the operating wavelength
• CPC Class Codes: H04B 17/103 Reflected power, e.g. return loss
• CPC Class Codes: H04B 17/14 of the whole transmission and reception path, e.g. self-test loop-back

Abstract

An electronic device may have control circuitry that uses a reflectometer to measure antenna impedance during operation. The reflectometer may have a directional coupler that is coupled between radio-frequency transceiver circuitry and an antenna. A calibration circuit may be coupled between the directional coupler and the antenna. The calibration circuit may have a first port coupled to the antenna, a second port coupled to the directional coupler, and a third port that is coupled to a calibration resistance. The reflectometer may have terminations of identical impedance that are coupled to ground. Switching circuitry in the reflectometer may be used to route signals from the directional coupler to a feedback receiver for measurement by the control circuitry or to ground through the terminations. Calibrated antenna reflection coefficient measurements may be used in dynamically adjusting the antenna.

Claims

1. An electronic device, comprising:

radio-frequency transceiver circuitry;

an antenna;

a transmission line path that couples the antenna to the radio-frequency transceiver circuitry;

a reflectometer coupled in the transmission line path between the antenna and the radio-frequency transceiver circuitry; and

a calibration circuit coupled between the reflectometer and the antenna.

2. The electronic device defined in claim 1 wherein the reflectometer comprises:

a feedback receiver;

first and second terminations of identical impedance that are coupled to ground;

a directional coupler; and

switching circuitry that is used in routing signals from the directional coupler to the feedback receiver and to ground.

3. The electronic device defined in claim 2 wherein the first and second terminations are characterized by a reflection coefficient and wherein the electronic device comprises control circuitry that stores the reflection coefficient to calibrate the reflectometer.

4. The electronic device defined in claim 3 wherein the calibration circuit has a first state in which a calibration resistance is switched into use and is coupled to the reflectometer and a second state in which the calibration resistance is switched out of use and the antenna is coupled to the reflectometer and wherein the reflection coefficient is determined by the control circuitry using forward path and reverse path measurements made using the directional coupler, the switching circuitry, and the feedback receiver.

5. The electronic device defined in claim 4 wherein the calibration circuit comprises a 50 ohm resistor that provides the calibration resistance.

6. The electronic device defined in claim 5 wherein the calibration circuit further comprises a switch controlled by the control circuitry that selectively couples the reflectometer to one of:

the 50 ohm resistor and the antenna.

7. The electronic device defined in claim 5 wherein the antenna comprises an inverted-F antenna resonating element.

8. The electronic device defined in claim 7 further comprising peripheral conductive housing structures, wherein the inverted-F antenna resonating element is formed from the peripheral conductive housing structures.

9. The electronic device defined in claim 4 wherein the calibration circuit comprises a switch connector.

10. The electronic device defined in claim 3 wherein the antenna comprises a hybrid inverted-F slot antenna.

11. The electronic device defined in claim 3 wherein the control circuitry is configured to calibrate the reflectometer and store the reflection coefficient by gathering both forward path measurements and reverse path measurements with the reflectometer.

12. A method of operating an electronic device having radio-frequency transceiver circuitry coupled to an antenna with a transmission line path, comprising:

with control circuitry in the electronic device, controlling a reflectometer interposed in the transmission line path to gather a calibrated reflection coefficient measurement for the antenna; and

taking action with the control circuitry based on the calibrated reflection coefficient measurement for the antenna.

13. The method defined in claim 12 wherein taking action with the control circuitry comprises adjusting the antenna.

14. The method defined in claim 13 wherein the reflectometer comprises a feedback receiver, first and second terminations of identical impedance f that are coupled to ground, a directional coupler, and switching circuitry that is used in routing signals from the directional coupler to the feedback receiver and to ground and wherein controlling the reflectometer comprises controlling the switching circuitry while measuring signals with the feedback receiver.

15. The method defined in claim 14 wherein a calibration circuit is coupled between the reflectometer and the antenna, the method further comprising:

transmitting and receiving signals with radio-frequency transceiver and the antenna while the calibration circuit couples the directional coupler to the antenna.

16. The method defined in claim 15 further comprising:

performing calibration operations for the reflectometer by transmitting and receiving signals with the radio-frequency transceiver while the calibration circuit couples the directional coupler to a calibration resistor.

17. The method defined in claim 16 wherein the antenna has an inverted-F antenna resonating element separated from an antenna ground by a gap and has adjustable circuitry that bridges the gap and wherein adjusting the antenna comprises tuning the antenna by adjusting the adjustable circuitry.

18. An electronic device, comprising:

a housing;

control circuitry in the housing;

radio-frequency transceiver circuitry;

an antenna;

a transmission line path that couples the antenna to the radio-frequency transceiver circuitry;

a reflectometer coupled in the transmission line path between the antenna and the radio-frequency transceiver circuitry, wherein the reflectometer is controlled by the control circuitry; and

a calibration circuit coupled between the reflectometer and the antenna.

19. The electronic device defined in claim 18 wherein the reflectometer comprises:

first and second terminations of identical impedance that are coupled to ground;

a directional coupler; and

switching circuitry that coupled between the directional coupler and the first and second terminations, wherein the switching circuitry is controlled by the control circuitry.

20. The electronic device defined in claim 19 wherein the antenna includes adjustable circuitry that is adjusted by the control circuitry based on calibrated reflection coefficient measurements made on the antenna with the reflectometer.

21. The electronic device defined in claim 20 wherein the calibration circuit comprises:

a calibration resistor; and

a switch having a first port coupled to the antenna, a second port coupled to the reflectometer, and a third port coupled to the calibration resistor.

22. The electronic device defined in claim 21 wherein the control circuitry stores a reflection coefficient for the terminations and wherein the electronic device housing comprises peripheral conductive structures that form part of the antenna.