Digital measurement circuit and system using a grounded capacitive sensor
US6700392B2 · kind B2 · utility
Inventor
Key dates
| Filing date | Jan 31, 2002 |
| Grant date | Mar 2, 2004 |
| Priority date | — |
| Expiry date | Feb 15, 2022 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R27/2605
- WIPO fieldMeasurement
- WIPO sectorInstruments
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 cir…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.