Methods and sensors for multiphase scanning in the fingerprint and touch applications
Techniques for multi-phase scanning based on pseudo-random sequences in capacitive fingerprint applications are described herein. In an example embodiment, a method performed by a processing device comprises: receiving measurements that are representative of a portion of a finger on a capacitive fingerprint sensor array, where the measurements are obtained from sensor elements of the capacitive fingerprint sensor array that are scanned in a multi-phase mode based on an excitation vector generated from a pseudo-random sequence; and generating a fingerprint image for the portion of the finger based on the measurements.
1. A method comprising:
receiving, by a processing device, a plurality of measurements that is representative of a portion of a finger on a capacitive fingerprint sensor array;
wherein the plurality of measurements is obtained from sensor elements of the capacitive fingerprint sensor array in a multi-phase scan based on an excitation vector generated by applying an autocorrelation function to a pseudo-random sequence;
generating, by the processing device, a fingerprint image for the portion of the finger based on the plurality of measurements.
2. The method of claim 1 , wherein the plurality of measurements represents mutual capacitances measured at the sensor elements of the capacitive fingerprint sensor array.
3. The method of claim 1 , wherein the fingerprint image is a set of data values that represents in digital format a fingerprint for the portion of the finger.
4. The method of claim 1 , wherein the pseudo-random sequence has data elements of +1 and 1.
5. The method of claim 4 , wherein the excitation vector represents polarities of control signals applied to multiplex multiple electrodes of the sensor elements.
6. The method of claim 1 , wherein the sensor elements of the capacitive fingerprint sensor array include receive (RX) electrodes, and the method further comprises:
generating an RX excitation matrix based on the excitation vector; and
multiplexing the RX electrodes to one or more differential receivers of the processing device according to the RX excitation matrix.
7. The method of claim 6 , wherein generating the fingerprint image comprises:
generating, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generating a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the RX excitation matrix.
8. The method of claim 1 , wherein the sensor elements of the capacitive fingerprint sensor array include transmit (TX) electrodes, and the method further comprises:
generating a TX excitation matrix based on the excitation vector; and
driving the TX electrodes according to the TX excitation matrix.
9. The method of claim 8 , wherein generating the fingerprint image comprises:
generating, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generating a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the TX excitation matrix.
10. The method of claim 1 , wherein the sensor elements of the capacitive fingerprint sensor array include transmit (TX) electrodes and receive (RX) electrodes, and the method further comprises:
generating a TX excitation matrix based on the excitation vector;
generating an RX excitation matrix based on the excitation vector;
driving the TX electrodes according to the TX excitation matrix; and
multiplexing the RX electrodes to one or more differential receivers of the processing device according to the RX excitation matrix;
wherein generating the fingerprint image comprises:
generating, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generating a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the TX excitation matrix or of the RX excitation matrix.
11. A system comprising:
a capacitive fingerprint sensor array; and
a processing device coupled to the capacitive fingerprint sensor array, the processing device configured at least to:
perform a multi-phase scan of the capacitive fingerprint sensor array based on an excitation vector generated by applying an autocorrelation function to a pseudo-random sequence;
receive a plurality of measurements that represents a portion of a finger on the capacitive fingerprint sensor array; and
generate a fingerprint image for the portion of the finger based on the plurality of measurements.
12. The system of claim 11 , wherein the plurality of measurements represents mutual capacitances measured at sensor elements of the capacitive fingerprint sensor array.
13. The system of claim 11 , wherein the fingerprint image is a set of data values that represents in digital format a fingerprint for the portion of the finger.
14. The system of claim 11 , wherein the pseudo-random sequence has data elements of +1 and 1.
15. The system of claim 14 , wherein the excitation vector represents polarities of control signals applied to multiplex multiple electrodes of the capacitive fingerprint sensor array.
16. The system of claim 11 , wherein the capacitive fingerprint sensor array includes receive (RX) electrodes, and the processing device is configured to:
generate an RX excitation matrix based on the excitation vector; and
multiplex the RX electrodes to one or more differential receivers according to the RX excitation matrix.
17. The system of claim 16 wherein, to generate the fingerprint image, the processing device is configured at least to:
generate, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generate a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the RX excitation matrix.
18. The system of claim 11 , wherein the capacitive fingerprint sensor array includes transmit (TX) electrodes, and the processing device is configured to:
generate a TX excitation matrix based on the excitation vector; and
drive the TX electrodes according to the TX excitation matrix.
19. The system of claim 18 wherein, to generate the fingerprint image, the processing device is configured at least to:
generate, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generate a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the TX excitation matrix.
20. The system of claim 11 , wherein the capacitive fingerprint sensor array includes transmit (TX) electrodes and receive (RX) electrodes, and the processing device is configured to:
generate a TX excitation matrix based on the excitation vector;
generate an RX excitation matrix based on the excitation vector;
drive the TX electrodes according to the TX excitation matrix; and
multiplex the RX electrodes according to the RX excitation matrix;
wherein, to generate the fingerprint image, the processing device is configured at least to:
generate, based on the plurality of measurements, an output signal matrix with convoluted digital values; and
generate a recovered image matrix representing the fingerprint image based on a multiplication product of the output signal matrix and a transpose matrix of the TX excitation matrix or of the RX excitation matrix.