To provide a capacitance detecting circuit and a method, and a finger print sensor, which improve S/N ratios by reducing the effects of disturbance noise, and detect a very small capacitance value Cs and a capacitance change value ΔCs of a sensor element constituted of row wires and column wires with sufficient sensitivity.
The capacitance detecting circuit comprises: a PN code generating means for detecting changes in the capacitance of a capacitance sensor of a matrix shape constituted by crossing the column wires across a plurality of the row wires, changing the phase of a created PN code in time-series order, and outputting a row drive signal; a row wire drive means for selecting and driving a plurality of row wires corresponding to the row drive signal; a capacitance detecting means connected to the column wires for outputting a detection voltage acquired by converting the sum of changes in the capacitance of intersection parts corresponding to the selected row wires into a voltage; and a decoding arithmetic circuit for decoding a data string of the detected voltage time-serially outputted from the capacitance detecting means by prescribed computations on the basis of the PN code and separating a voltage corresponding to a change in the capacitance of each intersection part.
COPYRIGHT: (C)2005,JPO&NCIPI
Junichi Saito
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Masatake Shiga
Tadashi Takahashi
Hideyuki Sugiura
Suzuki Mitsuyoshi
Yasuhiko Murayama
Tadao Takashiba