Patent ID: 8766650
Filing Date: 2014-07-01
Classification: G01D,G01P,G01R

Abstract:
1. 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, the operational amplifier having an inverting input node and a noninverting input node that receives a reference voltage; a first feedback capacitor for the operational amplifier; a first load capacitor for the operational amplifier; an offset capacitor coupled between the inverting input node and a feedback node, wherein the first feedback capacitor is coupled to the feedback node; a second feedback capacitor coupled to the feedback node; a second load capacitor for the operational amplifier; and a switching architecture associated with the capacitive sensing cell, the operational amplifier, the first feedback capacitor, and the first load capacitor; wherein the switching architecture reconfigures the capacitance-to-voltage interface circuit for operation in a plurality of different phases such that the operational amplifier is used for capacitance-to-voltage conversion and for voltage amplification; and wherein the switching architecture reconfigures the capacitance-to-voltage interface circuit into a plurality of configurations in which: when 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 are arranged 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, the capacitive sensing cell is disconnected from the operational amplifier; when 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 are thereafter switched from the reset configuration into an initial capacitance-to-voltage configuration, the capacitive sensing cell is connected to the operational amplifier; when 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 are thereafter switched from the initial capacitance-to-voltage configuration into a final capacitance-to-voltage configuration, a measured output voltage of the operational amplifier that is indicative of a measured difference in capacitance of the capacitive sensing cell is obtained; and when 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 are thereafter switched from the final capacitance-to-voltage configuration into an amplification topology, the measured output voltage of the operational amplifier is amplified into an output voltage.