A plurality of capacitive touch pad sensors are multiplexed to the input of a common charge transfer analog-to-digital converter (CTAD) under the control of a control logic circuit. The no-touch digital output of each touch pad is stored in a memory. The touch pads are then sequentially ...http://www.google.es/patents/US4145748?utm_source=gb-gplus-sharePatente US4145748 - Self-optimizing touch pad sensor circuit
