Capacitive proximity sensor in a mobile device and method of limiting radiation absorption

Abstract

A proximity sensor for detecting proximity of a body portion to a mobile device, comprising: a plurality of capacitive sensing electrodes for detecting said body portion, an electronic processing circuit arranged for measuring the capacities of said capacitive sensing electrodes and for generating a proximity signal based on the capacities so measured, wherein the capacitive sensing electrodes are connected together by one or more capacitive elements, and at least one capacitive sensing electrode is connectable to a radio circuit of said mobile device so as to constitute a radiofrequency antenna of said mobile device.

1 - 13 . (canceled) 
     
     
         14 . A connected portable device having a RF interface connected to an antenna for data transmission and reception in a radio band, wherein the antenna has a first section and a second section capacitively connected together, a multichannel proximity detector with a first input channel reading the capacity of the first section and a second input channel reading the capacity of the second section, wherein the first input channel and the second input channel have different sensitivities, and the multichannel proximity detector is arranged to generate a proximity signal based on the capacity of the first section and on the capacity of the second section indicating a body part of an user approaching the antenna. 
     
     
         15 . The connected portable device of  claim 14 , wherein the first section is first side of the antenna, the second section is on a second side of the antenna, a RF field emitted by the antenna is more intense at the first side than at the second side, and the sensitivity of the second channel is lower than the side of the first channel. 
     
     
         16 . The connected portable device of  claim 14 , configured to determine a power reduction of the RF interface upon detection of a proximity from the proximity detector, wherein the power reduction has a level determined according to which section has detected a proximity. 
     
     
         17 . The connected portable devices of  claim 14 , wherein the first section and second section are connected to said multichannel proximity detector by inductive elements. 
     
     
         18 . The connected portable devices of  claim 14 , wherein the multichannel proximity detector is arranged to reject events characterized by a change of the capacitance seen by any one of the first section and second section with a speed exceeding a given threshold value. 
     
     
         19 . The connected portable devices of  claim 14 , wherein the multichannel proximity detector is arranged to accept events characterized by a change of the capacitance seen by any one of the first section and second section from a first essentially constant value to a second essentially constant value. 
     
     
         20 . The connected portable devices of  claim 14 , wherein the multichannel proximity detector is arranged to generate a proximity value based on a weighted sum of the capacities, or of the variations of capacitance of the first section and second section. 
     
     
         21 . The connected portable devices of  claim 14 , wherein the antenna has further sections in addition to the first section and second section, and the multichannel proximity detector has a corresponding number of channels. 
     
     
         22 . The connected portable device of  claim 14 , wherein the radio band is in the UHF spectrum, in particular in a band of the UHF spectrum assigned to cellular phone services, Wi-Fi, or Bluetooth, and the multichannel proximity detector operates in a band of frequency below the radio band.