Multiple capacitance measuring circuits and methods

Abstract

In capacitance measurement circuits and methods that measure capacitances at multiple locations by ramping voltage signals between reference levels, the phase of the voltage signal ramping can be controlled, for example to mitigate currents flowing between measurement locations. Such capacitance measurement circuits and methods can be utilized in touch sensor devices that determine touch position based on capacitance measurements on multiple locations on a touch surface. Controlling the phase of the voltage signal ramps can include concurrently starting the voltage signal ramps, for example by effecting a delay on at least one signal channel that has reached a voltage threshold, or by regulating all the voltage ramps according to a fixed frequency.

1 . For use in a touch sensor device that measures capacitances at a plurality of locations on a touch surface in response to a touch object coupling to the touch surface at a touch position, the capacitances being measured by applying electrical charge to the plurality of locations to ramp respective voltage signals between a first reference level and a second reference level, the method comprising:
 controlling the phase of the voltage signal ramps to mitigate currents flowing between the locations.   
   
   
       2 . The method of  claim 1 , wherein the voltage signal ramps are alternated between ramping up from the first reference level to the second reference level and ramping down from the second reference level to the first reference level, and wherein controlling the phase comprises concurrently ramping up the voltage levels and concurrently ramping down the voltage levels. 
   
   
       3 . The method of  claim 1 , wherein the voltage signals are ramped in the same direction, from the first reference level to the second reference level, with a reset back to the first reference level between each ramp, and wherein controlling the phase comprises concurrently ramping the voltage levels and concurrently resetting the voltage levels. 
   
   
       4 . The method of  claim 1 , wherein applying electrical charge to the plurality of locations includes applying a continuous current, applying a pulsed current, or applying a voltage through an impedance. 
   
   
       5 . The method of  claim 1 , wherein controlling the phase of the voltage signal ramps comprises concurrently starting the voltage signal ramps. 
   
   
       6 . The method of  claim 5 , wherein concurrently starting the voltage signal ramps comprises effecting a delay on at least one voltage signal ramp that has reached a threshold level prior to other voltage signal ramps reaching the threshold level. 
   
   
       7 . The method of  claim 6 , wherein the delay is a predetermined delay started upon the at least one voltage signal reaching the threshold level. 
   
   
       8 . The method of  claim 6 , further comprising adjusting the delay to minimize average differences among the voltage signal ramps. 
   
   
       9 . The method of  claim 5 , wherein the voltage signal ramps are regulated by a period timer that starts the voltage signal ramps at the same time according to a fixed frequency. 
   
   
       10 . The method of  claim 1 , wherein controlling the phase of the voltage signal ramps comprises determining time differentials between when respective voltage signal ramps reach a threshold level, and using the determined time differentials to adjust subsequent ramp starting times. 
   
   
       11 . The method of  claim 1 , further comprising measuring capacitances associated with each location by measuring ramp times for respective voltage signal ramps. 
   
   
       12 . The method of  claim 11 , further comprising using the measured capacitances to determine the touch position. 
   
   
       13 . A touch sensor device that measures capacitances at a plurality of locations on a touch surface in response to a touch object coupling to the touch surface at a touch position, the capacitances being measured by applying electrical charge to the plurality of locations to ramp respective voltage signals between a first reference level and a second reference level, the device comprising:
 a signal control circuit that controls the phase of the voltage signal ramps to mitigate currents flowing between the locations.   
   
   
       14 . The touch sensor device of  claim 13 , wherein the signal control circuit controls the phase by concurrently starting the voltage signal ramps. 
   
   
       15 . The touch sensor device of  claim 14 , wherein the signal control circuit concurrently starts the voltage signal ramps by effecting a delay on at least one voltage signal ramp that has reached a threshold level prior to other voltage signal ramps reaching the threshold level. 
   
   
       16 . The touch sensor device of  claim 15 , wherein the delay is a predetermined delay started upon the at least one voltage signal reaching the threshold level. 
   
   
       17 . The touch sensor device of  claim 15 , wherein the signal control circuit adjusts the delay to minimize average differences among the voltage signal ramps. 
   
   
       18 . The touch sensor device of  claim 14 , wherein the signal control circuit regulates the voltage signal ramps using a period timer that starts each voltage signal ramp at the same time according to a fixed frequency. 
   
   
       19 . The touch sensor device of  claim 13 , wherein the signal control circuit controls the phase of the voltage signal ramps by determining time differentials between when respective voltage signal ramps reach a threshold level, and using the determined time differentials to adjust subsequent ramp starting times. 
   
   
       20 . For use with a device that measures capacitances at a plurality of locations, each location associated with a capacitance measurement channel to ramp respective voltage signals on the respective capacitances, a method comprising:
 (a) concurrently initiating forward-direction voltage signal ramps on multiple channels; and   (b) effecting a delay on the forward-direction voltage signal ramp of at least one channel in response to reaching a high voltage signal threshold.   
   
   
       21 . The method of  claim 20 , further comprising:
 (c) concurrently initiating reverse-direction voltage signal ramps on the multiple channels; and   (d) effecting a delay on the reverse-direction voltage signal ramp of at least one channel in response to reaching a low voltage signal threshold.   
   
   
       22 . The method of  claim 21 , further comprising repeating steps (a) through (c) after step (d). 
   
   
       23 . The method of  claim 20 , wherein the delay is adjusted to minimize differences among forward-direction and reverse direction voltages. 
   
   
       24 . The method of  claim 20 , further comprising counting clock cycles for the multiple channels during the voltage signal ramps and correlating the number of clock cycles for a given channel with the capacitance being measured by the given channel. 
   
   
       25 . The method of  claim 24 , wherein voltage signal ramp initiation steps are synchronized with a clock cycle. 
   
   
       26 . The method of  claim 20 , wherein the delay ends upon all of the multiple channels having reached the high voltage signal threshold. 
   
   
       27 . The method of  claim 20 , wherein the delay ends after a predetermined time.