Capacitive sensor circuit
US5498914A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 30, 1994 |
| Grant date | Mar 12, 1996 |
| Priority date | — |
| Expiry date | Jun 30, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH03K17/955
- WIPO fieldBasic communication processes
- WIPO sectorElectrical engineering
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.