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 between a first electrode and a second electrode, comprising:
a switching circuit connected to the first electrode, controlled to change a voltage level of the first electrode; a transconductance amplifier mirror circuit including a first output port and a second output port, the first output port being controlled to connect to the second electrode, the transconductance amplifier mirror circuit being operative to maintain a voltage level of the first output port at a reference voltage, wherein when the voltage level of the first output port decreases, 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 a voltage level of the second 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.