Mitigation of parasitic capacitance in self capacitance touch sensing

Abstract

Self capacitance touch circuits to cancel the effects of parasitic capacitance in a touch sensitive device are disclosed. One circuit can generate a parasitic capacitance cancelation signal that can be injected into touch sensing circuitry to cancel the parasitic capacitance. Another circuit can adjust the phase and magnitude of the parasitic capacitance cancelation signal based on characteristics of channels in the touch sensing circuitry so as to fine tune the parasitic capacitance cancelations. Another circuit can drive a guard plate and touch panel electrodes so as to cancel the parasitic capacitances between the panel and the plate and between the electrodes.

What is claimed is: 
     
         1 . A touch sensing system, comprising:
 sensing circuitry configured to receive a touch signal from one or more touch electrodes of a touch sensor panel, wherein the sensing circuitry comprises:
 a first buffer configured to receive the touch signal and output a first output signal; and 
 a second buffer configured to receive the first output signal and output a second output signal as an output signal of the sensing circuitry, 
   wherein the first buffer and the second buffer are configured to operate with one or more supply voltages that are below a voltage level of the touch signal.   
     
     
         2 . The touch sensing system of  claim 1 , wherein the first buffer is a differential pair input buffer, a first input of the first buffer is the touch signal, and a second input of the first buffer is a touch stimulation signal. 
     
     
         3 . The touch sensing system of  claim 2 , wherein the touch signal, the touch stimulation signal, and the second output signal are common-mode adjusted signals. 
     
     
         4 . The touch sensing system of  claim 1 , wherein the touch signal and the second output signal are common-mode adjusted signals. 
     
     
         5 . The touch sensing system of  claim 1 , wherein the first buffer and the second buffer are configured to operate with a shared supply voltage. 
     
     
         6 . The touch sensing system of  claim 1 , wherein the first buffer is configured to operate with a first voltage supply and the second buffer is configured to operate with a second voltage supply, different from the first voltage supply. 
     
     
         7 . The touch sensing system of  claim 1 , wherein the first buffer has a common-mode input range above a voltage supply of the first buffer. 
     
     
         8 . The touch sensing system of  claim 1 , wherein a voltage supply voltage of the first buffer is less than a voltage of the touch signal. 
     
     
         9 . The touch sensing system of  claim 2 , wherein a voltage supply voltage of the first buffer is less than a voltage of the touch signal. 
     
     
         10 . The touch sensing system of  claim 7 , wherein the voltage supply voltage of the first buffer is less than a voltage of a touch stimulation signal. 
     
     
         11 . The touch sensing system of  claim 1 , wherein a common-mode input range of the first buffer includes a voltage of the touch signal. 
     
     
         12 . The touch sensing system of  claim 1 , wherein:
 the first buffer is configured to operate with a boosted supply voltage when the voltage level of the touch signal is above or equal to a second supply voltage of the second buffer.   
     
     
         13 . A method of operating a touch sensing system, the method comprising:
 receiving, by sensing circuitry, a touch signal from one or more touch electrodes of a touch sensor panel, including receiving, by a first buffer of the sensing circuitry, the touch signal;   outputting, by the first buffer, a first output signal;   receiving, by a second buffer of the sensing circuitry, the first output signal;   outputting, by the second buffer, a second output signal as an output signal of the sensing circuitry; and   operating the first buffer and the second buffer with one or more supply voltages that are below a voltage level of the touch signal.   
     
     
         14 . A non-transitory computer-readable storage medium including instructions, which when executed by a processor of a touch sensing system, cause the touch sensing system to perform a method comprising:
 receiving, by sensing circuitry, a touch signal from one or more touch electrodes of a touch sensor panel, including receiving, by a first buffer of the sensing circuitry, the touch signal;   outputting, by the first buffer, a first output signal;   receiving, by a second buffer of the sensing circuitry, the first output signal;   outputting, by the second buffer, a second output signal as an output signal of the sensing circuitry; and   operating the first buffer and the second buffer with one or more supply voltages that are below a voltage level of the touch signal.