Method for acquiring fingerprints
AssigneeIdemia Identity & Security France
InventorJoël-Yann Fourre
Life of this patent
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Abstract
Method for acquiring a fingerprint, performed by a device comprising an active thermal sensor when it is electrically supplied at a distance by a terminal, said sensor comprising a plurality of pixels, each pixel comprising a pyroelectric capacitor which, when it is subjected to a variation in temperature, generates electrical charges, each pixel being associated with a heating element adapted for heating said pixel and being connected to a reading circuit able to measure the electrical charges generated by said capacitor. The method relies on a taking into account of the heating element received by each pixel of said sensor (33, 34) in order to determine when said pixel is able to provide (36) a signal that can be used for generating information representing a part of a fingerprint.
Claims8
A method for acquiring information representing a fingerprint performed by a device comprising an active thermal sensor on which a body part carrying a fingerprint is placed at the time of a presentation at a distance of said device in front of a reading terminal producing an electromagnetic field able to generate an electrical supply in said device, said sensor comprising a plurality of pixels, each pixel comprising a thermosensitive element able to convert a variation in temperature into a variation in a parameter representing a measurable electrical property of said thermosensitive element, referred to as an electrical parameter, each pixel being associated with a heating element adapted for heating said pixel and being connected to a reading circuit able to measure the variations in said electrical parameter, the method comprising:
- for each pixel:
- initiating a heating-activation phase comprising:
- performing a first reinitialisation of the reading circuit connected to said pixel;
- and activating a heating of said pixel by the heating element corresponding to said pixel;
- ending the first reinitialisation after a predetermined heating period;
- ending the heating by the heating element when a heating energy produced in the pixel by said heating element reaches a predetermined heating energy;
- measuring a first item of information representing variations in the electrical parameter of said pixel after a predetermined waiting period, the first item of information corresponding to a period, referred to as an integration period, lying between the end of the first initiation and the end of the predetermined waiting period;
- performing a second reinitialisation of the reading circuit connected to said pixel;
- measuring, without heating by the heating element, a second item of information representing variations in the electrical parameter of said pixel after a period equal to the integration period following the end of the second reinitialisation;
- and
- calculating a third item of information representing variations in the electrical parameter of said pixel in the form of a difference between said first and said second item of information;
- the information representing the fingerprint being obtained from the third item of information calculated for each pixel.
A device comprising an active thermal sensor allowing acquisition of information representing a fingerprint when a body part carrying a fingerprint is placed on said thermal sensor, said device being adapted for being electrically supplied at a distance by a reading terminal producing an electromagnetic field, said sensor comprising a plurality of pixels, each pixel comprising a thermosensitive element able to convert a variation in temperature into a variation in a parameter representing a measurable electrical property of said thermosensitive element, referred to as an electrical parameter, each pixel being associated with a heating element adapted for heating said pixel and being connected to a reading circuit able to measure the variations in said electrical parameter, the device being configured to:
- for each pixel:
- initiate a heating-activation phase comprising:
- performing a first reinitialisation of the reading circuit connected to said pixel;
- and activating a heating of said pixel by the heating element corresponding to said pixel;
- end the first reinitialisation after a predetermined heating period;
- end the heating by the heating element when a heating energy produced in the pixel by said heating element reaches a predetermined heating energy;
- measure a first item of information representing variations in the electrical parameter of said pixel after a predetermined waiting period, the first item of information corresponding to a period, referred to as an integration period, lying between the end of the first initiation and the end of the predetermined waiting period;
- perform a second reinitialisation of the reading circuit connected to said pixel;
- measure, without heating by the heating element, a second item of information representing variations in the electrical parameter of said pixel after a period equal to the integration period following the end of the second reinitialisation;
- and
- calculate a third item of information representing variations in the electrical parameter of said pixel in the form of a difference between said first and said second item of information;
- the information representing the fingerprint being obtained from the third item of information calculated for each pixel.
Dependencies are inferred from the claim text.