Patent ID: 9562937
Date: 2017-02-07
CPC Classifications: G01D,G01R,G06F,H03F

Claim:
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.