Capacitive proximity detection system and method
A touch screen controller system for controlling a touch screen having row conductors and column conductors includes analog-digital circuitry coupled to the row conductors and column conductors to produce digital signals representative of self capacitance changes of one of the column conductors during an element proximity scanning mode and also representative of mutual changes of the touch screen during an element location scanning mode. The analog-digital circuitry indicates the influence of an element on the self-capacitance during the element proximity scanning. Proximity-determining circuitry operates on the digital signal changes during the element proximity scanning to determine if the element is proximate to the touch screen, and also to determine if the element is a specific kind of element by comparing the digital signal changes to a predetermined data profile.
1. A system comprising:
a touch screen including columns of conductors, and
touch screen controller circuitry coupled to the touch screen, the circuitry to:
compare voltages of ones of a first set of the columns of conductors to a first threshold, ones of the columns of conductors to be included in the first set of the columns based on a level of noise associated with the system;
based on comparison of the voltages of ones of the first set of the columns of conductors with the first threshold:
identify a first one of the columns of conductors having a highest voltage; and
compare the highest voltage to a second threshold;
based on a comparison of the highest voltage to the second threshold, compare a difference between the highest voltage and a lowest voltage of the columns of conductors to a third threshold; and
based on a comparison of the difference to the third threshold:
determine the touch screen is within a threshold proximity of a face of a user; and
change a setting of the system from an out-of-proximity state to an in-proximity state.
2. The system of claim 1 , wherein the touch screen controller circuitry is disposed within a mobile phone and the touch screen controller circuitry is to operate at a sampling rate of less than 30 samples per second during proximity testing performed during an ongoing phone call.
3. The system of claim 1 , wherein the touch screen controller circuitry is to reduce a sampling rate of a proximity detect circuitry of the touch screen controller circuitry.
4. The system of claim 1 , wherein the touch screen controller circuitry is to introduce hysteresis to maintain the status as in-proximity when the touch screen is no longer in-proximity of the face for an amount of time before the touch screen controller circuitry changes the status to the out-of-proximity state.
5. A method to determine a proximity of a face of a user to a touch screen, the method comprising:
when, as determined by touch screen controller circuitry, (i) voltages of ones of a first set of a plurality of columns of conductors of a touch screen are determined to meet a first threshold, and (ii) a highest voltage of a plurality of voltages corresponding respectively to ones of the plurality of columns of conductors is determined to meet a second threshold, performing, with the touch screen controller circuitry, a comparison of a difference between the highest voltage and a lowest voltage of the plurality of voltages to a third threshold, ones of the plurality of columns of conductors to be included in the first set of the plurality of columns of conductors based on a level of noise associated with the system;
when the difference between the highest voltage and the lowest voltage meets the third threshold, determining the touch screen is within a threshold proximity of the face of the user; and
changing a setting of the touch screen controller circuitry from an out-of-proximity state to an in-proximity state.
6. The method of claim 5 , wherein the touch screen controller circuitry and the touch screen are disposed in a mobile phone and the method includes reducing a sampling rate of a proximity detect circuitry of the touch screen controller circuitry during an ongoing phone call.
7. The method of claim 5 , wherein the method includes, causing the touch screen controller circuitry to operate at a sampling rate of less than 30 samples per second during proximity testing performed during an ongoing phone call.
8. The method of claim 5 , further including, when the touch screen is no longer in-proximity of the face, maintaining the proximity status as in-proximity for a duration of time before changing the proximity status to the out-of-proximity state.
9. The method of claim 8 , further including introducing hysteresis to maintain the status of the proximity testing circuit as in-proximity for the duration of time.
10. The method of claim 5 , further including energizing the plurality of the columns of conductors.