Proximity sensing based on antenna impedance variation

DETAILED DESCRIPTION The present invention provides a simple system and method for proximity detection representing a desirable alternative to the capacitive and other sensing systems and methods referred to above.
More particularly, the present invention provides a system and method for detecting the presence of a hand or other body part based on changes in antenna impedance caused by the proximity of a hand or body part.
Such changes in antenna impedance affect the amount of RF signal energy that the antenna reflects back into a transmission line connecting the antenna to a RF signal generator.
Among other benefits, the present invention offers a potentially simpler and more economic manner of detecting presence of a user that, when used with wireless devices, can avoid or reduce the need for separate sensing components.
In one embodiment, the proximity detection system includes a RF signal source.
A transmission pathway connects the RF source to an antenna.
A directional coupler has a main line electrically connected to the transmission pathway, as well as a coupled line.
The directional coupler produces a signal on the coupled line in response to changes in antenna and transmission line impedance mismatching caused by the presence of an object or body portion.
A signal detector is in electrical communication with the coupled line, and responds to signals produced in the coupled line by the main line.
The signal detector produces an output signal that is within an output range, the output range corresponding to a range of antenna-transmission line impedance mismatch.
A controller is in communication with the signal detector and configured to provide, in relation to the output signal, a state signal indicative of the presence or absence of an object or body portion.
A proximity detector according to the invention can also be incorporated into an input device having a controller that generates data signals in response to manipulation of the device by a user.
A RF signal source provides modulated RF signals for transmission of the data signals to another device, and the proximity detection is based upon the amount of the modulated RF signal that is reflected by the antenna because of impedance mismatch