Proximity Detection Using an Antenna and Directional Coupler Switch

• US 20130210477A1
• Filed: 02/12/2013
• Published: 08/15/2013
• Est. Priority Date: 02/15/2012
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Peter, Dieter
• Granted Patent: US 9,144,051 B2
• Time in Patent Office: Days
• US Class Current: 455/522
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H01Q 1/50 Structural association of antennas with earthing switches, lead-in devices or lightning protectors
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H04B 1/3838 Arrangements for reducing RF exposure to the user, e.g. by changing the shape of the transceiver while in use
• CPC Class Codes: H04B 17/103 Reflected power, e.g. return loss
• CPC Class Codes: H04W 52/18 TPC being performed according to specific parameters
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Detection of an increase in a mismatch of an antenna of a radio frequency (RF) device and/or a change in a capacitance value of the antenna indicates proximity of a body to the antenna. Upon detection of proximity of a body to the antenna, reduction of transmit power of the RF device may be done to meet Specific Absorption Rate (SAR) level regulations.

Claims

1. A directional coupler for coupling an antenna with a radio frequency (RF) system, comprising:

a first connection for coupling the antenna to a directional coupler switch arranged within the directional coupler;

a second connection for coupling the RF system to the antenna through the directional coupler switch; and

a third connection for coupling the antenna to a capacitance measurement device through the directional coupler switch, wherein the capacitance measurement device measures capacitance values of the antenna.

2. The directional coupler according to claim 1, further comprising a return loss bridge coupled between the directional coupler switch and the first connection.

3. The directional coupler according to claim 2, wherein the return loss bridge provides a reflected power measurement.

4. The directional coupler according to claim 1, further comprising a voltage standing wave ratio bridge coupled between the directional coupler switch and the first connection.

5. The directional coupler according to claim 4, wherein the voltage standing wave ratio bridge provides a reflected voltage standing wave measurement.

6. The directional coupler according to claim 1, wherein the directional coupler switch is a three position switch.

7. The directional coupler according to claim 1, wherein the capacitive measurement device comprises a charge time measurement unit (CTMU).

8. The directional coupler according to claim 1, wherein the capacitive measurement device comprises a capacitive voltage divider (CVD) circuit.

9. The directional coupler according to claim 1, wherein the capacitive measurement device comprises an oscillator and frequency discriminator circuit.

10. The directional coupler according to claim 1, further comprising a microcontroller coupled to and controlling the directional coupler switch.

11. A radio frequency device, comprising:

a radio frequency subsystem;

a power amplifier coupled to the radio frequency subsystem;

a low noise amplifier coupled to the radio frequency subsystem;

an antenna; and

a directional coupler comprising

a first connection for coupling the antenna to a directional coupler switch arranged within the directional coupler;

a second connection for coupling the power amplifier to the antenna through the directional coupler switch;

a third connection for coupling the low noise amplifier to the antenna through the directional coupler switch; and

a fourth connection for coupling the antenna to a capacitance measurement device through the directional coupler switch, wherein the capacitance measurement device measures capacitance values of the antenna.

12. The radio frequency device according to claim 11, further comprising a return loss bridge coupled between the directional coupler switch and the first connection.

13. The radio frequency device according to claim 12, wherein the return loss bridge provides a reflected power measurement.

14. The radio frequency device according to claim 11, further comprising a voltage standing wave ratio bridge coupled between the directional coupler switch and the first connection.

15. The radio frequency device according to claim 14, wherein the voltage standing wave ratio bridge provides a reflected voltage standing wave measurement.

16. The radio frequency device according to claim 11, wherein the directional coupler switch is a three position switch.

17. A method for determining proximity of a object to an antenna of a radio frequency device, said method comprising the steps of:

measuring a capacitance value of the antenna;

determining whether the measured capacitance value of the antenna has changed from a previous measurement of a capacitance value of the antenna; and

detecting proximity of the object to the antenna when the capacitive value of the antenna has changed by at least a certain value.

18. The method according to claim 17, further comprising the steps of:

measuring a reflected voltage standing wave value of the antenna;

determining whether the reflected voltage standing wave value of the antenna has changed from a previous measurement of a reflected voltage standing wave value of the antenna; and

detecting proximity of the object to the antenna when the reflected voltage standing wave value of the antenna has changed by at least a certain value.

19. The method according to claim 17, further comprising the step of reducing transmit power of the radio frequency device when detecting proximity of the object to the antenna.

20. A method for determining proximity of a object to an antenna of a radio frequency device, said method comprising the steps of:

measuring a reflected voltage standing wave value of the antenna;

determining whether the reflected voltage standing wave value of the antenna has changed from a previous measurement of a reflected voltage standing wave value of the antenna; and

detecting proximity of the object to the antenna when the reflected voltage standing wave value of the antenna has changed by at least a certain value.

21. The method according to claim 20, further comprising the steps of:

measuring a capacitance value of the antenna;

determining whether the measured capacitance value of the antenna has changed from a previous measurement of a capacitance value of the antenna; and

detecting proximity of the object to the antenna when the capacitive value of the antenna has changed by at least a certain value.

22. The method according to claim 20, further comprising the step of reducing transmit power of the radio frequency device when detecting proximity of the object to the antenna.