Fingerprint sensing system
AssigneeNXP B.V.
InventorThomas Suwald
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Abstract
It is described an arrangement (560, 660, 760) for fingerprint sensing/verification, comprising: a sensor system (100) comprising plural sensor capacitors (101), each sensor capacitor including a central electrode (103) and a peripheral electrode (105) annularly surrounding the central electrode and being connected to a ground potential; wherein changes of the electric fields between each of the central electrode and the peripheral electrode of the plural sensor capacitors upon positioning a finger (317) close to the sensor system is used to detect the fingerprint.
Claims10
Arrangement for fingerprint sensing/verification, comprising:
- a sensor system comprising plural sensor capacitors, each sensor capacitor including
- a central electrode
- a peripheral electrode annularly surrounding the central electrode and being connected to a ground potential;
- and
- a readout system adapted to selectively generate an output signal indicative of a capacity of each of the plural sensor capacitors, the readout system comprising a capacitance-to-voltage converter adapted to convert a capacity of each of the plural sensor capacitors to a voltage proportional to the capacity, the capacitance-to-voltage converter comprising a sample capacitor connectable to an output terminal of an operational amplifier to sample an output voltage of the readout capacitor, an analog-to-digital converter for converting the voltage of the sample capacitor to a numerical value, wherein the analog-to-digital converter has a non-linear conversion characteristic and wherein a reference voltage and/or capacity of a readout capacitor is computer controllable;
- wherein changes of the electric fields between each of the central electrode and the peripheral electrode of the plural sensor capacitors upon positioning a finger close to the sensor system is used to detect the fingerprint topology,
- wherein a change of the electric field changes a capacity of the respective sensor capacitor.
Method of fingerprint sensing/verification, comprising:
- using a sensor system comprising plural sensor capacitors, each sensor capacitor including
- a central electrode
- a peripheral electrode annularly surrounding the central electrode and being connected to a ground potential;
- and
- an image cache having a capacity of between 16 kB and 128 kB;
- the method comprising:
- positioning a finger close to the sensor system, thereby
- changing electric fields between each of the central electrode and the peripheral electrode of the plural sensor capacitors;
- detecting the changes in the electric fields thereby sensing the fingerprint in an overview area of the finger at a low resolution, and
- identifying, in the overview area, detail-rich sub areas including at least one ridge ending and/or ridge island and/or ridge bifurcation and/or ridge crossing and/or a ridge-flow feature;
- detecting fingerprint features in the sub areas at a high resolution, a sum of the sizes of the sub areas between 20% and 50% of a size of the overview area, wherein identifying the detail-rich sub areas comprises converting the low resolution representation into a frequency/wavelet domain and calculating a Haar wavelet transform and analyzing its frequency content, and
- wherein a change of the electric field changes a capacity of the respective sensor capacitor.
Dependencies are inferred from the claim text.