Capacitive fingerprint sensor with adjustable gain
US6538456B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Jan 11, 2000 |
| Grant date | Mar 25, 2003 |
| Priority date | — |
| Expiry date | Jan 11, 2020 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG07C9/37
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The present invention relates to a fingerprint sensing device comprising a planar array of closely-spaced capacitive sense elements. When a finger is placed in close proximity to the sensing device, the capacitive sense elements measure a capacitance between the finger and a single capacitor plate in each sense element. This is accomplished by precharging each capacitor plate, and then using a known current source to remove a fixed amount of charge from each capacitor plate. The measured capacitance varies as a function of the distance between the capacitor plate and the finger surface. Thus, a capacitance measurement allows the distance between the capacitor plate and the finger surface to be determined. Distance measurements across the array of sense elements are combined to produce a representation of the pattern of ridges on the finger surface which comprise a fingerprint. After a fingerprint is acquired, the quality of the fingerprint is evaluated, and if necessary, a gain parameter for the sense elements is iteratively adjusted until a satisfactory fingerprint is acquired.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.