CIRCUIT AND METHOD FOR SENSING A CAPACITANCE

摘要

A transconductance amplifier mirror circuit is connected to an electrode for sensing the capacitance of the electrode with reference to ground, or the capacitance between the electrode and another electrode. A voltage level change is produced on the electrode connected to the transconductance amplifier mirror circuit to cause the transconductance amplifier mirror circuit to supply charges to or drain charges from a charge calculation circuit. The charge amount variation is converted to a signal for calculating the sensed capacitance.

主权项

1. A circuit for sensing a capacitance of an electrode with reference to ground, comprising:
a switching circuit connected to the electrode, controlled to change a voltage level of the electrode; a transconductance amplifier mirror circuit including a first output port and a second output port, operative to maintain a voltage level of the first output port at a reference voltage; a sensing switch connected between the electrode and the first output port of the transconductance amplifier mirror circuit, controlled to connect the first output port to the electrode, wherein when the voltage level of the electrode is lower than the reference voltage and the sensing switch is turned on, the transconductance amplifier mirror circuit supplies a first amount of charges to the first output port and a second amount of charges to the second output port responsive to a difference between the voltage level of the electrode and the reference voltage; and a charge calculation circuit connected to the second output port of the transconductance amplifier mirror circuit, operative to generate a sensed signal responsive to the second amount of charges; wherein the second amount of charges is proportional to the first amount of charges.