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Capacitive Keyboard FET Sense Circuit

IP.com Disclosure Number: IPCOM000053533D
Original Publication Date: 1981-Oct-01
Included in the Prior Art Database: 2005-Feb-12

Publishing Venue

IBM

Related People

Authors:
Crabtree, EG Sublette, JM Thomas, DR [+details]

Abstract

The circuit shown uses an on-chip reference capacitance for digital sensing of the status of a capacitive keyboard. A signal of one polarity shift is produced when the keyboard is operated, and a signal of the opposite polarity shift is produced when the key is unoperated. To optimize the response, the exact reference capacitance is selected digitally. The digital input may be found in a power-on sequence.