Capacitance to code converter with sigma-delta modulator

摘要

An apparatus and method of converting a capacitance measured on a sensor element to a digital value. The apparatus may include a matrix-scanning device including drive lines and sense lines. A sense element is located at an intersection of one of the drive lines and one of the sense lines. The apparatus also includes a modulation circuit coupled to the drive lines and the sense lines, and a switching circuit having first switches controlled by a clock. The modulation circuit is configured to measure a mutual capacitance on the sense element and to convert the measured mutual capacitance to a first digital value. The modulation circuit is configured to measure a self-capacitance on at least one of the drive lines and to convert the measured self-capacitance to a second digital value.

主权项

1. A method comprising:
measuring a mutual capacitance on a sense element of a matrix-scanning device using a modulation circuit, wherein the matrix-scanning device comprises a plurality of drive lines and a plurality of sense lines and the sense element is located at an intersection of one of the plurality of drive lines and one of the plurality of sense lines, wherein the measuring the mutual capacitance comprises:
applying a drive signal to the one of the plurality of drive lines using an excitation source; andsensing, by the modulation circuit, the drive signal on the one of the plurality of sense lines to measure the mutual capacitance of the sense element; and switching the sense element to be coupled and decoupled to a capacitor of the modulation circuit using a first plurality of switches, wherein the first plurality of switches are controlled by a clock; converting the mutual capacitance measured on the sense element to a first digital value; measuring a self-capacitance on at least one of the plurality of drive lines; switching the at least one of the plurality of drive lines to be coupled and decoupled to the capacitor using a second plurality of switches, wherein the second plurality of switches are controlled by the clock; and converting the self-capacitance measured on the at least one of the plurality of drive lines to a second digital value.