Proximity detection using an antenna and directional coupler switch
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.
1. 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 through a return loss bridge coupled between the antenna and a directional coupler switch operable to switch between a plurality of ports, wherein the directional coupler switch comprises at least a first port coupled with an RF subsystem;
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.
2. The method according to claim 1 , further comprising the steps of: measuring a capacitance value of the antenna through a capacitance measurement device coupled with a second port of the directional coupler switch;
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.
3. The method according to claim 1 , further comprising the step of reducing transmit power of the radio frequency device when detecting proximity of the object to the antenna.
4. The method according to claim 1 , said method further comprising the steps of:
controlling a switching device to decouple the antenna from a radio frequency subsystem and couple the antenna with the capacitance measurement device;
controlling the capacitance measurement device to measure 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.
5. The method according to claim 4 , 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.
6. The method according to claim 4 , further comprising the step of reducing transmit power of the radio frequency device when detecting proximity of the object to the antenna.
7. A mobile device with proximity detection functionality, comprising: a digital processor,
an antenna,
a return loss bridge or voltage standing wave bridge coupled between the antenna and a directional coupler switch, wherein the return loss bridge or voltage standing wave bridge comprises a processor interface coupled with the digital processor,
wherein the digital processor is operable to measure a reflected voltage standing wave value of the antenna, to determine 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 to detect proximity of user operating the mobile device to the antenna when the reflected voltage standing wave value of the antenna has changed by at least a certain value.
8. The mobile device according to claim 7 , wherein the return loss bridge provides a reflected power measurement.
9. The mobile device according to claim 7 , wherein the voltage standing wave ratio bridge provides a reflected voltage standing wave measurement.
10. The mobile device according to claim 7 , wherein the device directional coupler switch is controlled by the digital processor for coupling the antenna with a radio frequency (RF) system, wherein the device directional coupler switch comprises:
a first connection for coupling an output of the return loss bridge or voltage standing wave bridge to a directional coupler switch arranged within the device directional coupler;
a second connection for coupling the RF system to the output of the return loss bridge or voltage standing wave bridge through the directional coupler switch; and
a third connection for coupling the output of the return loss bridge or voltage standing wave bridge to a capacitance measurement device through the directional coupler switch,
wherein the digital processor is further operable to measure a capacitance value of the antenna through the capacitance measurement device when said directional coupler switch is controlled to couple the antenna with the capacitance measurement device and further to determine whether the measured capacitance value of the antenna has changed from a previous measurement of a capacitance value of the antenna, and to detect proximity of an object to the antenna when the capacitive value of the antenna has changed by at least a certain value.
11. The mobile device according to claim 10 , wherein the directional coupler switch is a three position switch.
12. The mobile device according to claim 10 , wherein the capacitive measurement device comprises a charge time measurement unit (CTMU).
13. The mobile device according to claim 10 , wherein the capacitive measurement device comprises a capacitive voltage divider (CVD) circuit.
14. The mobile device according to claim 10 , wherein the capacitive measurement device comprises an oscillator and frequency discriminator circuit.
15. A radio frequency device, comprising: a digital processor;
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;
a return loss bridge or voltage standing wave bridge coupled between the antenna and a directional coupler, wherein the return loss bridge is coupled with the digital processor and wherein the directional coupler comprises
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 digital processor is operable to select either said second, third or fourth connection and to measure a reflected voltage standing wave value of the antenna, to determine 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 to detect proximity of an object to the antenna when the reflected voltage standing wave value of the antenna has changed by at least a certain value.
16. The radio frequency device according to claim 15 , wherein the processor is further operable to measure a capacitance value of the antenna through the capacitance measurement device when said directional coupler switch is controlled to couple the antenna with the capacitance measurement device and further to determine whether the measured capacitance value of the antenna has changed from a previous measurement of a capacitance value of the antenna, and to detect proximity of an object to the antenna when the capacitive value of the antenna has changed by at least a certain value.
17. The radio frequency device according to claim 15 , wherein the voltage standing wave ratio bridge provides a reflected voltage standing wave measurement.
18. The radio frequency device according to claim 15 , wherein the directional coupler switch is a three position switch.