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. 02, 2004
Filed:
Jan. 31, 2002
Wayne C. Haase, Sterling, MA (US);
Other;
Abstract
A circuit and system for sensing and measuring the mutual capacitance between a sensor capacitor having one grounded lead and a target and providing a direct digital output of the measured capacitance is disclosed. The circuit and system includes a relaxation oscillator coupled to a sensor capacitor and a fixed resistor. The fixed resistor and the sensor capacitor in conjunction with the relaxation oscillator provide a time varying output signal that has a period that is proportional to the mutual capacitance of the sensor capacitor and a target and resistance of the fixed resistor. The circuit and system can also include circuitry to compensate for the input capacitance of one or more amplifiers used in the relaxation oscillator. The circuit and system can also include circuitry to effectively increase the resistance of the fixed resistor by a predetermined constant. This allows a smaller resistance value for the fixed resistor to be used with the concomitant reduction in the size of the fixed resistor, which reduces the parasitic capacitance of the fixed resistor. A guard electrode can be formed coaxially surrounding the fixed resistor and coupled to an input amplifier in the circuit to further reduce the parallel parasitic capacitance of the fixed resistor. An interval timer can be coupled to the output of the relaxation oscillator to provide an accurate measurement of the period of the output signal. This value, or the frequency of the output signal, may be used by a calculation module to accurately determine the value of the mutual capacitance and the value of the measured variable. In addition, the system may include predetermined calibration signals that are used as correction values.