BIOMETRIC SKIN CONTACT SENSOR AND METHOD OF OPERATING A BIOMETRIC SKIN CONTACT SENSOR

A biometric skin contact sensor comprising an array of sensor pixels, wherein each sensor pixel comprises: a capacitive sensing electrode for accumulating a charge in response to proximity of a conductive object to be sensed; a reference capacitor connected to the capacitive sensing electrode; a sense voltage-controlled impedance, VCI, having a control terminal connected to a connection between the capacitive sensing electrode and the reference capacitor, the sense VCI having an impedance controlled by its control terminal voltage, and wherein the pixel is arranged so that, in response to a select voltage being applied to the pixel, the control terminal voltage of the sense VCI indicates the proximity of the conductive object to be sensed; and biasing circuitry comprising a one-way conduction path from a bias voltage connection to the control terminal of the sense VCI so that current flows from the bias voltage towards the control terminal of the sense VCI in response to the control terminal voltage of the sense VCI dropping below a floor value.