04639720 is referenced by 230 patents and cites 9 patents.

A graphics input/output device contains a graphics input pad having an array of transparent capacitive pixels the capacitance characteristics of which are changed in response to the passing of a conductive-tipped stylus over the surface of the pad. This change in capacitance is sensed by sense buffers disposed along the columns of the matrix, as the rows are scanned at a prescribed scanning rate.

The sensed data is read out of the sense buffer and loaded into a RAM. An array of display pixels formed of an LCD matrix is addressed by a scan sequence control unit, and the energization of the display pixels is multiplexed with the read-out scanning of the sensed data, so as to present to the user a real time generated image of the graphics created by the stylus. As a result, it appears to the user that the stylus is actually "writing" on the display pad.

Title
Electronic sketch pad
Application Number
6/224067
Publication Number
4639720
Application Date
January 12, 1981
Publication Date
January 27, 1987
Inventor
Roger L Ritenour
Palm Bay
FL, US
James S Herstein
Satellite Beach
FL, US
William P Rympalski
Melbourne
FL, US
Agent
Antonelli Terry & Wands
Assignee
Harris Corporation
FL, US
IPC
G09G 3/00
View Original Source