Object position detector

Abstract

An object proximity sensor includes a capacitive touch-sensitive transducer including row conductive lines insulated from column conductive lines to from a matrix. An insulating layer is disposed over the matrix and has a thickness selected to achieve significant capacitive coupling between an object placed on its surface and the matrix. Circuitry first drives each of the row conductive lines to a fixed voltage and then simultaneously injects a known amount of charge onto each of the row conductive lines, and then senses for each row conductive line a row-sense voltage created by the known amount of charge injected onto each of the row conductive lines, and, simultaneous with injected the known amount of charge, changes the voltage on all of the column conductive lines in the same direction as the row-sense voltage by an amount no greater than about twice the difference between the fixed voltage and an average of all row-sense voltage in the transducer. Circuitry first drives each of the column conductive lines to a fixed voltage and then simultaneously injects a known amount of charge onto each of the column conductive lines, and then senses for each column conductive line a column-sense voltage created by the known amount of charge injected onto each of the column conductive lines, and, simultaneous with injecting the known amount of charge, changes the voltage on all of the row conductive lines in the same direction as the column-sense voltages by an amount no greater than about twice the difference between the fixed voltage and an average of all column-sense voltages in the transducer. A set of object-sensed electrical signals related to all of the row-sense voltages and all of the column-sense voltages is produced.