Reducing sleep current in a capacitance sensing system
AssigneeCypress Semiconductor Corporation
InventorDavid G. Wright
Life of this patent
Estimating the term…
Abstract
An apparatus and method of measuring a collective capacitance on a group of capacitive sense elements from at least one of rows or columns of a capacitance sense array when in a first mode, and individually measuring capacitances on each of the rows and columns when in a second mode.
Claims18
A capacitance sensing device comprising:
- a first capacitance sensing electrode;
- a second capacitance sensing electrode;
- a capacitance measurement circuit coupled to the first capacitance sensing electrode and the second capacitance sensing electrode through a selection circuit, the capacitance measurement circuit for converting a first capacitance on the first capacitance sensing electrode to a first digital value and for converting a second capacitance on the second capacitance sensing electrode to a second digital value in a first mode and for converting the first capacitance on the first capacitance sensing electrode and the second capacitance on the second capacitance sensing electrode to a third digital value in a second mode, the third digital value representative of a combined capacitance of the first and second capacitance sensing electrodes;
- and
- a processor coupled to the capacitance measurement circuit and for:
- determining an activation state for the first and second capacitance sensing electrodes by a conductive object in the first mode,
- providing control signals to the selection circuit for operation of the capacitance measurement circuit in the second mode,
- performing a baseline measurement operation for the combined capacitance of the first and second capacitance sensing electrodes when the first and second capacitance sensing electrodes are not activated by the conductive object,
- determining an activation state for the first and second capacitance sensing electrodes by a conductive object in the second mode, and
- placing the capacitance sensing device into a reduced power mode if the first and second sensing electrodes are not activated by the conductive object in either the first mode or the second mode.
A capacitance measurement circuit coupled to a first capacitance sensing electrode and a second capacitance sensing electrode through a selection circuit, the capacitance measurement circuit for converting a first capacitance on the first capacitance sensing electrode to a first digital value and for converting a second capacitance on the second capacitance sensing electrode to a second digital value in a first mode and for converting the first capacitance on the first capacitance sensing electrode and the second capacitance on the second capacitance sensing electrode to a third digital value in a second mode, the third digital value representative of a combined capacitance of the first and second capacitance sensing electrodes, wherein the third digital value, if less than a threshold causes a controller coupled to the capacitance measurement circuit to enter a low power state.
Dependencies are inferred from the claim text.