An apparatus detects the approach and touch-down of an object relative to a sensor panel. The apparatus includes a digital filter for determining a first derivative of a current flow in the sensor panel and a controller determines when the first derivative reaches a maximum. In a preferred embodiment,...http://www.google.com.au/patents/US6343519?utm_source=gb-gplus-sharePatent US6343519 - Method and apparatus for touch detection based on the velocity of an object relative to a sensor panel
