Telegraphy – Systems – Position coordinate determination for writing
Patent
1989-07-20
1990-05-01
Schreyer, Stafford D.
Telegraphy
Systems
Position coordinate determination for writing
340706, G08C 2100
Patent
active
049220616
ABSTRACT:
A capacitive touch panel system (10) having a faceplate (14) with an electrically conductive layer (20) of a consistent resistivity employs a position measurement apparatus (12) to generate an address signal indicative of a position (46) on the faceplate in contact with a stylus (48). The position measurement apparatus includes a position measurement signal source (56) that generates a square-wave measurement signal of a frequency that varies in a substantially random manner. The position measurement signal is applied to a first pair of opposed electrodes (36) and (40) and a second pair of opposed electrodes (38) and (42) positioned along respective side margins (26, 30, 28, and 32) of the faceplate. The resistivity of the conductive layer establishes effective resistances of R.sub.x and R.sub.y between the respective first and second pairs of electrodes. Position measurement subcircuits (54a-54d) are locked-in with the random measurement signal frequencies to measure currents drawn through the electrodes whenever the stylus contacts the conductive layer, thereby to form an address signal indicative of the location at which the stylus contacts the faceplate. The random measurement signal frequencies reduce the susceptibility of the position measurement apparatus to electromagnetic noise and distributes over a relatively broad bandwidth the electromagnetic noise generated by the position measurement apparatus.
REFERENCES:
patent: 4476463 (1984-10-01), Ng et al.
patent: 4680430 (1987-07-01), Yoshikawa et al.
patent: 4698460 (1987-10-01), Krein et al.
patent: 4698461 (1987-10-01), Meadows et al.
patent: 4707845 (1987-11-01), Krein et al.
McCoy Roger J.
Meadows R. David
Meininger Mark M.
Schreyer Stafford D.
Tektronix Inc.
Winkelman John D.
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