Capacitive sensor filtering apparatus, method, and system

A capacitive sensor apparatus comprising:

• a sensor electrode;
• and
• a control circuit electrically connected to the sensor electrode, the control circuit configured to:
• periodically excite the sensor electrode and thereby periodically generate an electric field about the sensor electrode and a capacitance between the sensor electrode and a reference potential;
• periodically determine in the time domain values of capacitance between the sensor electrode and the reference potential;
• continuously transform a rolling sample of the periodically-determined values of capacitance from the time domain to a plurality of data signals in the sequency domain using a Walsh-Hadamard Transform, each of the data signals in a corresponding sequency bin resulting from the Walsh-Hadamard Transform and each of the data signals comprising values related to capacitance for corresponding samples of the rolling sample;
• analyze in the sequency domain at least one of the plurality of data signals in the corresponding sequency bin;
• and
• determine whether a touch event has occurred based on the analysis of the at least one of the plurality of data signals in the corresponding sequency bin,
• wherein the rolling sample is an n-point rolling sample including a current sample and n−1 samples immediately preceding the current sample,
• wherein the n−1 samples includes a last sample, wherein n=2x and x is an integer greater than or equal to 2,
• wherein n is an integer corresponding to a size of a Walsh matrix used in performance of the Walsh-Hadamard Transform, and
• wherein performance of the Walsh-Hadamard Transform yields n sequency bins numbered 0 through n−1.