Position measurement apparatus for capacitive touch panel system

Patent 4853498 Issued on August 1, 1989. Estimated Expiration Date:

June 13, 2008. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.

Abstract Claims Description Full Text

Patent References

Display device having unpatterned touch detection
Patent #: 4476463
Issued on: 10/09/1984
Inventor: Ng , et al.

Touch panel with automatic nulling Patent #: 4707845
Issued on: 11/17/1987
Inventor: Krein , et al.

Inventors

Assignee

Tektronix, Inc.

Application

No. 07/205896 filed on 06/13/1988

US Classes:

345/174, Including impedance detection345/179Stylus

Examiners

Primary: Schreyer, Stafford D.

Attorney, Agent or Firm

International Class

G06F 3/033 (20060101)

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 (62) that generates a square-wave measurement signal of substantially constant frequency and a preselected magnitude. 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 Rx and Ry between the respective first and second pairs of electrodes. Position measurement subcircuits (60a-60d) 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.