Control method and electronic stylus for touch input to a capacitive touchpad module

Abstract

An electronic stylus emits an excitation signal to apply to a trace of a capacitive touchpad module near a touch point when the electronic stylus touches the capacitive touchpad module, so as to change a waveform of a charging/discharging signal in the trace, and depending on the waveform variation, the capacitive touchpad module can identify the touch point.

What is claimed is: 
     
         1 . A control method for an apparatus including an electronic stylus and a capacitive touchpad module for touch input, the control method comprising the steps of:
 (A) generating an excitation signal having a constant phase difference from a charging/discharging signal in a trace of the capacitive touchpad module;   (B) supplying the excitation signal to a tip of the electronic stylus;   (C) emitting the excitation signal by the tip to apply to the trace of the capacitive touchpad module near a touch point when the tip touches the capacitive touchpad module, so as to change a waveform of the charging/discharging signal in the trace; and   (D) sensing the touch point according to an amplitude of the waveform.   
     
     
         2 . The control method of  claim 1 , wherein the step A comprises the step of setting a frequency of the excitation signal equal to an integral multiple of a frequency of the charging/discharging signal. 
     
     
         3 . The control method of  claim 1 , wherein the step A comprises the step of setting a frequency of the excitation signal equal to a frequency of the charging/discharging signal and a duty ratio of the excitation signal equal to 50%. 
     
     
         4 . The control method of  claim 1 , wherein the step A comprises the step of operating an oscillation circuit to generate the excitation signal. 
     
     
         5 . The control method of  claim 1 , wherein the step A comprises the steps of:
 detecting the charging/discharging signal from the trace to generate a detection signal;   up-converting the detection signal to generate a high-frequency signal;   transmitting the high-frequency signal to the electronic stylus; and   receiving and down-converting the high-frequency signal to generate the excitation signal.   
     
     
         6 . The control method of  claim 1 , wherein the step A comprises the steps of:
 detecting the charging/discharging signal from the trace to generate a detection signal;   modulating the detection signal to generate a modulated carrier signal;   transmitting the modulated carrier signal to the electronic stylus; and   receiving and demodulating the modulated carrier signal to generate the excitation signal.   
     
     
         7 . The control method of  claim 1 , wherein the step B comprises the steps of:
 detecting the charging/discharging signal from the trace to generate a detection signal which is related to a phase and a frequency of the charging/discharging signal;   embedding data representing the detection signal into a carrier signal;   transmitting the carrier signal to the electronic stylus;   extracting the data from the carrier signal; and   generating the excitation signal according to the extracted data.   
     
     
         8 . An electronic stylus for touch input to a capacitive touchpad module, comprising:
 an oscillation circuit generating an excitation signal having a constant phase difference from the charging/discharging signal;   a power circuit connected to the oscillation circuit, providing a supply voltage for the oscillation circuit; and   a tip connected to the oscillation circuit, emitting the excitation signal to apply to a trace of the capacitive touchpad module near a touch point when the electronic stylus touches the capacitive touchpad module, so as to change a waveform of a charging/discharging signal in the trace.   
     
     
         9 . The electronic stylus of  claim 8 , wherein the oscillation circuit comprises:
 a boost circuit connected to the power circuit, boosting the supply voltage to generate a boosted voltage; and   a quartz oscillator connected to the boost circuit, driven by the boosted voltage to generate the excitation signal.   
     
     
         10 . The electronic stylus of  claim 8 , wherein the power circuit generates the supply voltage according to a radio frequency signal transmitted from the capacitive touchpad module. 
     
     
         11 . The electronic stylus of  claim 8 , wherein the power circuit transforms a magnetic force into the supply voltage. 
     
     
         12 . The electronic stylus of  claim 8 , wherein the power circuit comprises a battery providing the supply voltage. 
     
     
         13 . The electronic stylus of  claim 8 , further comprising a switch being turned on or off to control whether or not to emit the excitation signal. 
     
     
         14 . The electronic stylus of  claim 8 , wherein the tip comprises a metal. 
     
     
         15 . The electronic stylus of  claim 8 , wherein the tip comprises a flexible conductor. 
     
     
         16 . The electronic stylus of  claim 8 , wherein the tip comprises a metal wrapped by a nonconductor. 
     
     
         17 . The electronic stylus of  claim 8 , further comprising:
 a metal wrapping around the tip;   a first insulator wrapping around the metal for shielding against ambient interference; and   a second insulator between the tip and the metal for separating the tip from the metal.   
     
     
         18 . The electronic stylus of  claim 8 , wherein the excitation signal has a frequency equal to an integral multiple of a frequency of the charging/discharging signal. 
     
     
         19 . The electronic stylus of  claim 8 , wherein the excitation signal has a frequency equal to a frequency of the charging/discharging signal and a duty ratio of 50%.