The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 12, 1996
Filed:
Jun. 30, 1994
Jan R De Boer, Drachten, NL;
U.S. Philips Corporation, New York, NY (US);
Abstract
A capacitive sensor circuit is provided which comprises: a sensor electrode (16) forming a first plate of a sensing capacitor (14) relative to a reference terminal (10), a first (2) and a second (26) inverting Schmitt trigger having the same threshold voltages. A feedback resistor (8) provides feedback from the output (6) to the input (4) of the first trigger (2), which together with the sensing capacitor (14) forms an oscillator whose frequency depends on the magnitude of the sensing capacitor (14). The input (24) of the second trigger (26) is connected to the output of the first trigger (2) via a series resistor (22) and to the reference terminal (10) via a reference capacitor (30). The resistance values of the feedback resistor (8) and the series resistor (22) are equal. A d.c. signal will appear on the output (32) of the second trigger if the capacitance of the sensing capacitor (14) is smaller than the capacitance of the reference capacitor (30) and an a.c. signal in the opposite case.