Patent ID: 11961321
Assignee: TOUCH BIOMETRIX LIMITED
Field: Computer technology (Electrical engineering)
Classification: CPC G | IPC G

Claim 13:
14. A method of operating a biometric skin contact sensor comprising an array of sensor pixels, wherein each sensor pixel comprises: (i) a capacitive sensing electrode for accumulating a charge in response to proximity of a conductive object to be sensed, (ii) a reference capacitor, and (iii) a sense voltage-controlled impedance, VCI, having a control terminal connected to a connection node between the capacitive sensing electrode and the reference capacitor, and wherein the sense VCI is arranged to have an impedance controlled by its control terminal voltage, wherein the method comprises:
resetting a charge on the reference capacitor to a selected value;
providing a one way conduction path between a bias voltage and a control terminal of the sense VCI so that the control terminal voltage is at a floor value;
applying a select voltage to the pixel after the control terminal voltage of the sense VCI has been set to the floor value, so that the control terminal voltage of the sense VCI indicates the proximity of the conductive object to be sensed.