Capacitive sensing apparatus and methods

Abstract

One or more waveform generators impose an input waveform across touch sensor components. Phase shift detection logic measures a phase shift between the input waveform and an output waveform component associated with each waveform generator appearing across a touch sensor component. Amplitude ratio detection logic measures an output-to-input waveform magnitude ratio associated with each waveform generator. Translator logic converts the phase shift(s) and optionally the output-to-input waveform magnitude ratio(s) to capacitance values. Validation logic compares the resulting capacitance values to each other to determine consistency and validity during a particular waveform sampling time. The phase shift detection logic and the amplitude ratio detection logic are optionally implemented with discrete Fourier transform logic which includes narrow-band filtering to exclude electromagnetic interference frequency components from touch sensor signal measurements.

1 . A capacitive touch detection apparatus, comprising:
 a periodic waveform generator coupled across a series-connected resistive-capacitive (“RC”) network, the RC network to include a capacitive touch element C of variable capacitance C_TOUCH and a resistor R, C_TOUCH being a function of a proximity of a dielectric mass to C, the periodic waveform generator to generate a periodic voltage waveform of frequency F and to impose the periodic voltage waveform across the RC network;   a phase shift detector with a first input coupled across the RC network to receive the periodic voltage waveform and a second input communicatively coupled across a selected one of C or R to receive a decreased magnitude, phase-shifted version of the periodic voltage waveform appearing across the selected one of C or R, the phase shift detector to measure a phase shift φ_DIFF between the periodic voltage waveform and the decreased magnitude, phase-shifted version of the periodic voltage waveform; and   a phase shift to capacitance translator coupled to an output of the phase shift detector to convert φ_DIFF to a first measure of C_TOUCH based upon φ_DIFF (“C_TOUCH(φ_DIFF)”) as C_TOUCH(φ_DIFF)=(tan φ_DIFF)/(2*π*ƒ*R).   
     
     
         2 . The capacitive touch detection apparatus of  claim 1 , the periodic waveform generator selected from one of a sine wave generator, a triangular wave generator, a square wave generator, and a pulse wave generator. 
     
     
         3 . The capacitive touch detection apparatus of  claim 1 , further comprising:
 an amplitude ratio detector with a first input coupled across the RC network to receive the periodic voltage waveform and a second input communicatively coupled across the selected one of C or R to receive the decreased magnitude, phase-shifted version of the periodic voltage waveform, the amplitude ratio detector to measure an amplitude of the periodic voltage waveform and an amplitude of the decreased magnitude, phase-shifted version of the periodic voltage waveform and to determine a ratio (“A_RATIO”) of the amplitude of the decreased magnitude, phase-shifted version of the periodic voltage waveform to the amplitude of the periodic voltage waveform.   
     
     
         4 . The capacitive touch detection apparatus of  claim 3 , further comprising:
 an amplitude ratio to capacitance translator coupled to the amplitude ratio detector to convert A_RATIO to a second measure of C_TOUCH based upon A_RATIO (“C_TOUCH(A_RATIO)”) as C_TOUCH(A_RATIO)=[(1−A_RATIO**2)]**½/(2*π*ƒ*R*A_RATIO).   
     
     
         5 . The capacitive touch detection apparatus of  claim 3 , further comprising:
 an amplifier input-coupled across the selected one of C or R, an output of the amplifier coupled to at least one of the second input of the phase shift detector or the second input of the amplitude ratio detector, the amplifier to reduce impedance loading of the selected one of C or R by the phase shift detector, the amplitude ratio detector, or both.   
     
     
         6 . The capacitive touch detection apparatus of  claim 5 , further comprising:
 C_TOUCH validation logic coupled to the phase shift to capacitance translator and to the amplitude ratio to capacitance translator to receive C_TOUCH(φ_DIFF) and C_TOUCH(A_RATIO), to determine a difference between C_TOUCH(φ_DIFF) and C_TOUCH(A_RATIO), to determine whether the difference is greater than a maximum selected difference (“C_TOUCH_MAX_DIFF”), to output a value of C_TOUCH (“C_TOUCH_OUT) as a function of at least one of C_TOUCH(φ_DIFF) or C_TOUCH(A_RATIO) if the difference is less than or equal to C_TOUCH_MAX_DIFF, and to output an invalidity indication if the difference is greater than C_TOUCH_MAX_DIFF; and   a register coupled to the C_TOUCH validation logic to store the value of C_TOUCH_MAX_DIFF.   
     
     
         7 . A capacitive touch detection apparatus, comprising:
 at least one periodic waveform generator coupled across a series-connected resistive-capacitive (“RC”) network, the RC network to include a capacitive touch element C of variable capacitance C_TOUCH and a resistor R, C_TOUCH being a function of a proximity of a dielectric mass to C, each periodic waveform generator to generate a periodic voltage waveform of frequency F1, F2 . . . or FN of a known amplitude (“A_INPUT_F1”, “A_INPUT_F2” . . . or “A_INPUT_FN”) and a known phase value (“φ_INPUT_F1”, “φ_INPUT_F2” . . . or “φ_INPUT_FN”) and to impose a sum (“F_SUM”) of the periodic voltage waveforms across the RC network;   an analog-to-digital converter (“ADC”) communicatively coupled across a selected one of C or R to receive and to periodically sample a decreased magnitude, phase-shifted version of F_SUM appearing across the selected one of C or R according to a first sampling periodicity associated with the periodic voltage waveform of frequency F1, a second sampling periodicity associated with the periodic voltage waveform of frequency F2 . . . and an Nth sampling periodicity associated with the periodic voltage waveform of frequency FN and to output a numerical magnitude value corresponding to each periodic sample;   a discrete Fourier transform (“DFT”) logic module corresponding to each periodic waveform generator communicatively coupled to the ADC, each DFT logic module to perform DFT operations on a set of numerical magnitude values sampled according to the first sampling periodicity, the second sampling periodicity . . . or the Nth sampling periodicity from at least a portion of a cycle of the decreased magnitude, phase-shifted version of F_SUM, each DFT logic module to generate a real numerical output value (“I_OUT_F1”, “I_OUT_F2” . . . or “I_OUT_FN”) and an imaginary numerical output value (“Q_OUT_F1”, “Q_OUT_F2” . . . or “Q_OUT_FN”) for each set of numerical magnitude sample values;   at least one phase shift logic module, each phase shift logic module coupled to a corresponding DFT logic module to receive the I_OUT value and the Q_OUT value from the corresponding DFT logic module and to determine a phase shift (“φ_DIFF_F1”, “φ_DIFF_F2” . . . or “φ_DIFF_FN”) between the periodic voltage waveform of frequency F1, F2 . . . or FN associated with the corresponding DFT logic module and the decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN associated with the corresponding DFT logic module; and   at least one phase shift to capacitance translator, each phase shift to capacitance translator coupled to a corresponding phase shift logic module to determine a potential value of C_TOUCH “C_TOUCH(φ_DIFF_F1)”, “C_TOUCH(φ_DIFF_F2)” . . . or “C_TOUCH(φ_DIFF_FN)” corresponding to the phase shift between the periodic voltage waveform of frequency F1, F2 . . . or FN and the corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as C_TOUCH(φ_DIFF_F1)=(tan φ_DIFF_F1)/(2*π*F1*R), C_TOUCH(φ_DIFF_F2)=(tan φ_DIFF_F2)/(2*π*F2*R) . . . and C_TOUCH(φ_DIFF_FN)=(tan φ_DIFF_FN)/(2*π*FN*R), respectively.   
     
     
         8 . The capacitive touch detection apparatus of  claim 7 , each DFT logic module a single bin (“SB”) DFT logic module. 
     
     
         9 . The capacitive touch detection apparatus of  claim 7 , further comprising:
 at least one sample value table, each sample value table coupled to the ADC to store a corresponding set of numerical magnitude values sampled according to the first sampling periodicity, the second sampling periodicity . . . or the Nth sampling periodicity.   
     
     
         10 . The capacitive touch detection apparatus of  claim 7 , each phase shift logic module further comprising:
 an output phase calculator to determine an output phase value (“φ_OUTPUT_F1”, “φ_OUTPUT_F2” . . . or “φ_OUTPUT_FN”) associated with a corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as φ_OUTPUT_F1=arctan 2(I_OUT_F1,Q_OUT_F1), φ_OUTPUT_F2=arctan 2(I_OUT_F2,Q_OUT_F2) . . . and φ_OUTPUT_FN=arctan 2(I_OUT_FN,Q_OUT_FN1), respectively;   an input phase register to store the known input phase value φ_INPUT_F1, φ_INPUT_F2 . . . or φ_INPUT_FN associated with the corresponding periodic voltage waveform of frequency F1, F2 . . . or FN; and   a phase shift calculator coupled to the output phase calculator and to the input phase register to calculate the phase shift φ_DIFF_F1, φ_DIFF_F2 . . . or φ_DIFF_FN as φ_DIFF_F1=(φ_OUTPUT_F1)−(φ_INPUT_F1), φ_DIFF_F2=(φ_OUTPUT_F2)−(φ_INPUT_F2), and φ_DIFF_FN=(φ_OUTPUT_FN)−(φ_INPUT_FN), respectively.   
     
     
         11 . The capacitive touch detection apparatus of  claim 7 , further comprising:
 C_TOUCH validation logic coupled to each phase shift to capacitance translator to compare at least two of the potential values C_TOUCH(φ_DIFF_F1), C_TOUCH(φ_DIFF_F2) . . . and C_TOUCH(φ_DIFF_FN), to determine whether a difference between the potential values of C_TOUCH is greater than a selected value C_TOUCH_MAX_DIFFERENCE, to output a numerical average of the potential values of C_TOUCH as C_TOUCH_OUT if the difference between the potential values of C_TOUCH is not greater than the selected value C_TOUCH_MAX_DIFFERENCE, and to output an invalidity flag C_TOUCH_MEASUREMENT_INVALID if the difference between the potential values of C_TOUCH is greater than the selected value C_TOUCH_MAX_DIFFERENCE; and   a register coupled to the C_TOUCH validation logic to contain the selected value C_TOUCH_MAX_DIFFERENCE.   
     
     
         12 . The capacitive touch detection apparatus of  claim 7 , further comprising:
 at least one amplitude ratio logic module, each amplitude ratio logic module coupled to a corresponding DFT logic module to receive the I_OUT value and the Q_OUT value from the corresponding DFT logic module and to determine an amplitude ratio (“AR_F1”, AR_F2” . . . or “AR_FN”) of the decreased magnitude, phase-shifted version of the periodic voltage waveform associated with the corresponding DFT logic module to the periodic voltage waveform associated with the corresponding DFT logic module; and   at least one amplitude ratio to capacitance translator coupled to a corresponding amplitude ratio logic module to determine a potential value of C_TOUCH “C_TOUCH(AR_F1)”, “C_TOUCH(AR_F2)” . . . or “C_TOUCH(AR_FN)” corresponding to an amplitude ratio of the corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN to the periodic voltage waveform of frequency F1, F2 . . . or FN as C_TOUCH(AR_F1)=[(1−AR_F1**2)]**½/(2*π*F1*R*AR_F1), C_TOUCH(AR_F2)=[(1−AR_F2**2)]**½/(2*π*F2*R*AR_F2) . . . and C_TOUCH(AR_FN)=[(1−AR_FN**2)]**½/(2*π*FN*R*AR_FN), respectively.   
     
     
         13 . The capacitive touch detection apparatus of  claim 12 , each amplitude ratio logic module further comprising:
 an output amplitude calculator to determine an output amplitude value (“A_OUTPUT_F1”, “A_OUTPUT_F2” . . . or “A_OUTPUT_FN”) associated with a corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as A_OUTPUT_F1=sqrt[(I_OUT_F1)**2+(Q_OUT_F1)**2], A_OUTPUT_F2=sqrt[(I_OUT_F2)**2+(Q_OUT_F2)**2] . . . and A_OUTPUT_FN=sqrt[(I_OUT_FN)**2+(Q_OUT_FN)**2], respectively;   an input amplitude register to store the constant input amplitude value A_INPUT_F1, A_INPUT_F2 . . . or A_INPUT_FN associated with the corresponding periodic voltage waveform of frequency F1, F2 . . . or FN; and   an amplitude ratio calculator coupled to the output amplitude calculator and to the input amplitude register to determine an amplitude ratio (“AR_F1”, “AR_F2” . . . or “AR_FN”) of the corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN to the periodic voltage waveform of frequency F1, F2 . . . or FN as AR_F=A_OUTPUT_F1/A_INPUT_F1, AR_F2=A_OUTPUT_F2/A_INPUT_F2 . . . and AR_FN=A_OUTPUT_FN/A_INPUT_FN, respectively.   
     
     
         14 . The capacitive touch detection apparatus of  claim 12 , further comprising:
 C_TOUCH validation logic coupled to each phase shift to capacitance translator and to each amplitude ratio to capacitance translator to compare at least two of the potential C_TOUCH values C_TOUCH(φ_DIFF_F1), C_TOUCH(φ_DIFF_F2) . . . C_TOUCH(φ_DIFF_FN), C_TOUCH(AR_F1), C_TOUCH(AR_F2) . . . and C_TOUCH(AR_FN), to determine whether a difference between the potential C_TOUCH values is greater than a selected value C_TOUCH_MAX_DIFFERENCE, to output a numerical average of the potential C_TOUCH values as C_TOUCH_OUT if the difference between the potential C_TOUCH values is not greater than the selected value C_TOUCH_MAX_DIFFERENCE, and to output an invalidity flag C_TOUCH_MEASUREMENT_INVALID if the difference between the potential C_TOUCH values is greater than the selected value C_TOUCH_MAX_DIFFERENCE; and   a register coupled to the C_TOUCH validation logic to contain the selected value C_TOUCH_MAX_DIFFERENCE.   
     
     
         15 . The capacitive touch detection apparatus of  claim 12 , further comprising:
 C_TOUCH validation logic coupled to each phase shift to capacitance translator and to each amplitude ratio to capacitance translator to perform weighted averaging operations on the potential C_TOUCH values C_TOUCH(φ_DIFF_F1), C_TOUCH(φ_DIFF_F2) . . . C_TOUCH(φ_DIFF_FN), C_TOUCH(AR_F1), C_TOUCH(AR_F2) . . . and C_TOUCH(AR_FN) and to output a weighted average of the potential C_TOUCH values as C_TOUCH_OUT.   
     
     
         16 . A method of capacitive touch detection, comprising:
 imposing a sum (“F_SUM”) of at least one input periodic voltage waveform of frequency F1, F2 . . . FN of a known amplitude (“A_INPUT_F1”, “A_INPUT_F2” . . . or “A_INPUT_FN”) and known phase value (“φ_INPUT_F1”, “φ_INPUT_F2” . . . or “φ_INPUT_FN”) across a series-connected resistive-capacitive (“RC”) network, the RC network to include a capacitive touch element C of variable capacitance C_TOUCH and a resistor R, C_TOUCH a function of a proximity of a dielectric mass to C;   periodically sampling a decreased magnitude, phase-shifted version of F_SUM appearing across a selected one of C or R according to a first sampling periodicity associated with the input periodic voltage waveform of frequency F1, a second sampling periodicity associated with the input periodic voltage waveform of frequency F2 . . . and an Nth sampling periodicity associated with the input periodic voltage waveform of frequency FN;   performing discrete Fourier transform (“DFT”) operations on a set of numerical magnitude values sampled according to the first sampling periodicity, the second sampling periodicity . . . or the Nth sampling periodicity from at least a portion of a cycle of the decreased magnitude, phase-shifted version of F_SUM;   generating a real numerical output value (“I_OUT_F1”, “I_OUT_F2” . . . or “I_OUT_FN”) and an imaginary numerical output value (“Q_OUT_F1”, “Q_OUT_F2” . . . or “Q_OUT_FN”) from the DFT operations for each set of numerical magnitude sample values;   determining a phase shift (“φ_DIFF_F1”, “φ_DIFF_F2” . . . or “φ_DIFF_FN”) between the periodic voltage waveform of frequency F1, F2 . . . or FN and the decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN; and   determining a potential value of C_TOUCH “C_TOUCH(φ_DIFF_F1)”, “C_TOUCH(φ_DIFF_F2)” . . . or “C_TOUCH(φ_DIFF_FN)” corresponding to the phase shift between the periodic voltage waveform of frequency F1, F2 . . . or FN and the corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as C_TOUCH(φ_DIFF_F1)=(tan φ_DIFF_F1)/(2*π*F1*R), C_TOUCH(φ_DIFF_F2)=(tan φ_DIFF_F2)/(2*π*F2*R) . . . and C_TOUCH(φ_DIFF_FN)=(tan φ_DIFF_FN)/(2*π*FN*R), respectively.   
     
     
         17 . The method of capacitive touch detection of  claim 16 , further comprising:
 determining an output phase value (“φ_OUTPUT_F1”, “φ_OUTPUT_F2” . . . or “φ_OUTPUT_FN”) associated with a corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as φ_OUTPUT_F1=arctan 2(I_OUT_F1,Q_OUT_F1), φ_OUTPUT_F2=arctan 2(I_OUT_F2,Q_OUT_F2) . . . and φ_OUTPUT_FN=arctan 2(I_OUT_FN,Q_OUT_FN1), respectively; and   calculating the phase shift φ_DIFF_F1, φ_DIFF_F2 . . . or φ_DIFF_FN as φ_DIFF_F1=(φ_OUTPUT_F1)−(φ_INPUT_F1), φ_DIFF_F2=(φ_OUTPUT_F2)−(φ_INPUT_F2), and φ_DIFF_FN=(φ_OUTPUT_FN)−(φ_INPUT_FN), respectively.   
     
     
         18 . The method of capacitive touch detection of  claim 16 , further comprising:
 determining an output amplitude value (“A_OUTPUT_F1”, “A_OUTPUT_F2” . . . or “A_OUTPUT_FN”) associated with a corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN as A_OUTPUT_F1=sqrt[(I_OUT_F1)**2+(Q_OUT_F1)**2], A_OUTPUT_F2=sqrt[(I_OUT_F2)**2+(Q_OUT_F2)**2] . . . and A_OUTPUT_FN=sqrt[(I_OUT_FN)**2+(Q_OUT_FN)**2], respectively;   determining an amplitude ratio (“AR_F1”, “AR_F2” . . . or “AR_FN”) of the corresponding decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN to the periodic voltage waveform of frequency F1, F2 . . . or FN as AR_F1=A_OUTPUT_F1/A_INPUT_F1, AR_F2=A_OUTPUT_F2/A_INPUT_F2 . . . and AR_FN=A_OUTPUT_FN/A_INPUT_FN, respectively; and   determining a potential value of C_TOUCH “C_TOUCH(AR_F1)”, “C_TOUCH(AR_F2)” . . . or “C_TOUCH(AR_FN)” corresponding to the amplitude ratio of the decreased magnitude, phase-shifted version of the periodic voltage waveform of frequency F1, F2 . . . or FN to the periodic voltage waveform of frequency F1, F2 . . . or FN as C_TOUCH(AR_F1)=[(1−AR_F1**2)]**½/(2*π*F1*R*AR_F1), C_TOUCH(AR_F2)=[(1−AR_F2**2)]**½/(2*π*F2*R*AR_F2) . . . and C_TOUCH(AR_FN)=[(1−AR_FN**2)]**½/(2*π*FN*R*AR_FN), respectively.   
     
     
         19 . The method of capacitive touch detection of  claim 18 , further comprising:
 comparing at least two of the C_TOUCH potential values C_TOUCH(φ_DIFF_F1), C_TOUCH(φ_DIFF_F2) . . . C_TOUCH(φ_DIFF_FN), C_TOUCH(AR_F1), C_TOUCH(AR_F2) . . . and C_TOUCH(AR_FN) to determine whether a difference between the potential values of C_TOUCH is greater than a selected value C_TOUCH_MAX_DIFFERENCE;   generating a numerical average of the potential values of C_TOUCH as C_TOUCH_OUT if the difference between the potential values of C_TOUCH is not greater than the selected value C_TOUCH_MAX_DIFFERENCE; and   generating an invalidity flag C_TOUCH_MEASUREMENT_INVALID if the difference between the potential values of C_TOUCH is greater than the selected value C_TOUCH_MAX_DIFFERENCE.   
     
     
         20 . The method of capacitive touch detection of  claim 18 , further comprising:
 performing weighted averaging operations on the C_TOUCH potential values C_TOUCH(φ_DIFF_F1), C_TOUCH(φ_DIFF_F2) . . . C_TOUCH(φ_DIFF_FN), C_TOUCH(AR_F1), C_TOUCH(AR_F2) . . . and C_TOUCH(AR_FN); and   generating a weighted average of the potential values of C_TOUCH as C_TOUCH_OUT.