Embedded SAR based active gain capacitance measurement system and method

摘要

A system for measuring a capacitor (CSENj) precharges a CDAC (23) in a SAR converter (17) to a reference voltage (VAZ) and also precharges a first terminal (3-j) of the capacitor to another reference voltage (GND). During a measurement phase, the CDAC is coupled between an output and an input of an amplifier (31) and the capacitor also is coupled to the input of the amplifier, so as to redistribute charge between the capacitor and the CDAC. The amplifier generates an output voltage (VAMP) representing the capacitance being measured. The output voltage is stored in the CDAC. The SAR converter converts the output voltage to a digital value representing the capacitance being measured.

主权项

1. An apparatus comprising:
a capacitive touch screen panel; an active gain control circuit having:
an amplifier that is coupled to the capacitive touch screen panel;a switch that is coupled to the capacitive touch screen panel; anda first switching circuit that is coupled to the amplifier and the switch; a successive approximation register (SAR) analog-to-digital converter (ADC) having:
a capacitor bank that is coupled to the first switching circuit, wherein the capacitor bank includes a plurality of weighted capacitors that are coupled in parallel with one another between the first switching circuit and a node,wherein the node is located within the SAR ADC;a comparator that is coupled to the node;SAR logic that is coupled to the comparator; anda second switching circuit that is coupled to the first switching circuit and that is controlled by the SAR logic; and an active gain, wherein the node further comprises a first node, and wherein the capacitive touch screen panel further comprises a plurality of sensing capacitors that are arranged in an array having a plurality of rows and a plurality of columns, wherein each column is associated with at least one of a plurality of second nodes, and wherein each sensing capacitor for each column is coupled to its associated second node, wherein the first switching circuit further comprises: a plurality of first switches, wherein each first switch is coupled between at least one of the second nodes and a third node; and a plurality of second switches, wherein each second switch is coupled between the third node and at least one of the plurality of weighted capacitors, wherein the third node is part of the capacitive touch screen panel.