Smartcard including a fingerprint sensor
A smartcard includes a fingerprint sensor and a detector circuit comprising at least first and second electrodes that are insulated from each other and that form an open circuit. The first electrode and the second electrode is arranged in such a manner that. When a user applies a first finger on the fingerprint sensor and uses a second finger to grip the smartcard, the first finger contacts the first electrode and the second finger contacts the second electrode so as to form a loop that closes the open circuit. The detector circuit further comprises a filter circuit connected to the first electrode and to the second electrode, a generator arranged to generate first signals across the terminals of the filter circuit, and processor means arranged to acquire second signals and, from the second signals, to detect whether the first and second fingers include a fake finger.
1. A smartcard comprising:
a fingerprint sensor; and
a detector circuit comprising:
at least a first electrode and a second electrode, the first electrode being insulated from the second electrode, forming an open circuit in the detector circuit, the first electrode and the second electrode being arranged in such a manner that, when a user applies a first finger on the fingerprint sensor, the first finger is in contact with the first electrode and when the user applies a second finger on the second electrode a loop is formed that closes the open circuit,
a filter circuit connected to the first electrode and to the second electrode;
a generator arranged to generate first signals across terminals of the filter circuit; and
processor means arranged to acquire second signals from one of the first electrode and second electrode and, from the second signals, to detect whether the first finger and the second finger include a fake finger.
2. The smartcard according to claim 1 , wherein the first electrode is a bezel of the fingerprint sensor.
3. The smartcard according to claim 1 , wherein the first electrode is formed on an acquisition surface of the fingerprint sensor.
4. The smartcard according to claim 1 , wherein the first electrode and the second electrode are located on two opposite faces of the smartcard.
5. The smartcard according to claim 1 , wherein the first signals comprise sinusoidal signals, each having a distinct emission frequency, the processor means being arranged to acquire a respective second signal for each emission frequency.
6. The smartcard according to claim 5 , wherein the processor means are arranged to determine a voltage representative of each second signal so as to obtain a voltage signal as a function of emission frequency.
7. The smartcard according to claim 6 , wherein the processor means are arranged to differentiate the voltage signal as a function of emission frequency in order to obtain a differentiated signal, and to compare the differentiated signal with first reference data stored in a memory of the smartcard.
8. The smartcard according to claim 7 , wherein the first reference data comes from reference curves that are obtained prior to or during fabrication of the smartcard by taking measurements on real human fingers.
9. The smartcard according to claim 8 , wherein the first reference data comprises the coefficients of interpolation functions for the reference curves.
10. The smartcard according to claim 8 , wherein the first reference data comprises remarkable points of the reference curves.
11. The smartcard according to claim 5 , wherein the processor means are arranged to estimate a phase shift for each second signal in order to produce a phase shift signal as a function of emission frequency, and to compare the phase shift signal with second reference data stored in a memory of the smartcard.
12. The smartcard according to claim 1 , wherein the first signals are single-frequency signals.