Multi-tone stimulus capacitive sensing

Abstract

A capacitive touch sensing system with transmit electrodes and receive electrodes positioned to have mutual capacitances at electrode intersections called nodes. The capacitance at nodes deviate when touched. The system estimates a touch position by: generating a multi-tone drive signal for the drive electrode comprising a first drive sinusoidal signal having a first frequency and a second drive sinusoidal signal having a second frequency; driving the drive electrode with the multi-tone drive signal; sensing with the sense electrode a multi-tone-drive sense signal; frequency discriminating the multi-tone-drive sense signal to estimate a first multi-tone-drive sense signal characteristic for the first frequency and to estimate a second multi-tone-drive sense signal characteristic for the second frequency; combining the first multi-tone-drive sense signal characteristic and the second multi-tone-drive sense signal characteristic; and determining a deviation of the combined first and second multi-tone-drive sense signal characteristic.

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