Patent ID: 8125231

Claim:
In a capacitance-to-voltage interface circuit comprising a capacitive sensing cell having a first sensing capacitor coupled in series with a second sensing capacitor, an operational amplifier adapted for selective coupling to the capacitive sensing cell and having an inverting input node and a noninverting input node that receives a reference voltage, an offset capacitor coupled between the inverting input node and a feedback node, a first feedback capacitor coupled to the feedback node, a second feedback capacitor coupled to the feedback node, a first load capacitor for the operational amplifier, and a second load capacitor for the operational amplifier, a method of performing capacitance-to-voltage conversion, the method comprising: arranging the capacitive sensing cell, the operational amplifier, the offset capacitor, the first feedback capacitor, the second feedback capacitor, the first load capacitor, and the second load capacitor into a reset configuration to reset the first feedback capacitor, the second feedback capacitor, the first load capacitor, and the second load capacitor to respective initial voltages, wherein the capacitive sensing cell is disconnected from the operational amplifier for the reset configuration; thereafter, switching from the reset configuration to arrange the capacitive sensing cell, the operational amplifier, the offset capacitor, the first feedback capacitor, the second feedback capacitor, the first load capacitor, and the second load capacitor into an initial capacitance-to-voltage configuration, wherein the capacitive sensing cell is connected to the operational amplifier for the initial capacitance-to-voltage configuration; thereafter, switching from the initial capacitance-to-voltage configuration to arrange the capacitive sensing cell, the operational amplifier, the offset capacitor, the first feedback capacitor, the second feedback capacitor, the first load capacitor, and the second load capacitor into a final capacitance-to-voltage configuration; thereafter, obtaining a measured output voltage of the operational amplifier that is indicative of a measured difference in capacitance of the capacitive sensing cell, while operating in the final capacitance-to-voltage configuration; thereafter, switching from the final capacitance-to-voltage configuration to arrange the capacitive sensing cell, the operational amplifier, the offset capacitor, the first feedback capacitor, the second feedback capacitor, the first load capacitor, and the second load capacitor into an amplification topology; and thereafter, amplifying the measured output voltage of the operational amplifier into an output voltage, while operating in the amplification topology.