| 摘要 |
A capacitance-to-voltage interface circuit is utilized to obtain a voltage corresponding to a detected capacitance differential, which may be associated with the operation of a capacitive sensing cell. The interface circuit includes a capacitive sensing cell, an operational amplifier adapted for selective coupling to the capacitive sensing cell, a feedback capacitor for the operational amplifier, a load capacitor for the operational amplifier, and a switching architecture associated with the capacitive sensing cell, the operational amplifier, the feedback capacitor, and the load capacitor. During use, the switching architecture reconfigures the capacitance-to-voltage interface circuit for operation in a plurality of different phases. The different operational phases enable the single operational amplifier to be used for both capacitance-to-voltage conversion and voltage amplification. |
| 主权项 |
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 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; wherein the capacitance-to-voltage interface circuit is configurable 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; andwhen 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. |
