Time-averaged proximity sensor
A proximity sensor for a portable connected wireless device generating an immediate proximity status signal (PROXSTAT, 310 ) that becomes active when a part of a user's body is close to the proximity sensor, an averaging unit ( 259 ) that may include a FIFO buffer, averaging the immediate proximity status flag in a predetermined time window, and a decision unit generating a time-averaged proximity status flag ( 350 ) based on an averaged value of the immediate proximity status flag in the time window, for example when the averaged value exceeds a predetermined threshold. In embodiments, the sensor is configured to switch temporarily and repeatedly the time-averaged proximity status flag to an inactive state when the value of the averaged or accumulated value yields an active state of the time-averaged proximity status flag. This feature improves the connectivity when the sensor is used to limit the RF emission of mobile devices.
1 . A capacitive proximity sensor in a portable connected wireless device that includes a radio transmitter, the capacitive proximity sensor comprising a processing circuit configured to acquire a capacitance of a sense electrode and subtract drift and noise contributions from the capacitance and generate a digital variable that indicates that the sense electrode has detected a part of a user's body, an averaging unit including a FIFO buffer that is periodically supplied, following an update rate, with values of the digital variable, wherein the averaging unit is configured to produce an average value by averaging or accumulating values of the digital variable in the FIFO buffer within a time window that has a length of more than one minute, wherein the length of the time window is determined by a depth of the FIFO buffer and by the update rate, and a decision unit setting a time-averaged proximity status flag in an active state when the average value exceeds a predetermined threshold, wherein the capacitive proximity sensor is configured to reduce a power of the radio transmitter in response to the active state of the time-averaged proximity status flag, the averaging unit comprising an input logic gate configured to inhibit supplying of the values of the digital variable to the FIFO buffer when the average value exceeds the predetermined threshold.
2 . The capacitive proximity sensor of claim 1 , arranged to generate a combined proximity status flag that results from a logic operation on the digital variable and on the time-averaged proximity status flag.
3 . The capacitive proximity sensor of claim 2 , wherein the logic operation is selectable from: a logic OR; a logic AND.
4 . The capacitive proximity sensor of claim 1 , the averaging unit including a FIFO buffer with a selectable length.
5 . The capacitive proximity sensor of claim 1 , including a logic circuit configured to inhibit the transmission of further values of the digital variable to the averaging unit if the time-averaged proximity status flag is active, whereby the average value sinks below the predetermined threshold, the time-averaged proximity flag is set in an inactive state, the power of the radio transmitter is temporarily increased and further values of the digital variable are allowed into the averaging unit, causing the average value to exceed the predetermined threshold, the time-averaged proximity flag to be set in the active state and the power to be reduced again.
6 . The capacitive proximity sensor of claim 1 , the sense electrode being also an antenna of the radio transmitter emitting radio waves.
7 . The capacitive proximity sensor of claim 1 , the digital variable being a binary variable or a multi-bit variable.
8 . A portable connected wireless device comprising:
a radio transmitter,
a processing circuit configured to acquire a capacitance of a sense electrode and subtract drift and noise contributions from the capacitance and generate a digital variable that indicates that the sense electrode has detected a part of a user's body based on the capacitance of the sense electrode,
an averaging unit including a FIFO buffer that is periodically supplied, following an update rate, with values of the digital variable, wherein the averaging unit is configured to produce an average value by averaging or accumulating all the values of the digital variable in the FIFO buffer within a time window that has a length of more than one minute, wherein the length of the time window is determined by a depth of the FIFO buffer and by the update rate,
a decision unit setting a time-averaged proximity status flag in an active state when the average value exceeds a predetermined threshold, wherein the decision unit is configured to reduce a power of the radio transmitter in response to the active state of the time-averaged proximity status flag, the averaging unit comprises an input logic gate configured to inhibit supplying of the values of the digital variable to the FIFO buffer when the average value exceeds the predetermined threshold.
9 . The portable connected wireless device of claim 8 , including a logic circuit configured to inhibit the transmission of further values of the digital variable to the averaging unit if the average value exceeds the predetermined threshold, whereby the average value sinks below the predetermined threshold and the power of the radio transmitter is temporarily increased and further values of the digital variable counter are allowed into the averaging unit causing the average value to exceed the predetermined threshold and the power to be reduced again.
10 . The capacitive proximity sensor of claim 1 , wherein the input logic gate causes an increase in the power of the radio transmitter when a part of a user's body is detected by the sense electrode.