Methods and sensors for multiphase scanning in the fingerprint and touch applications

1. A method comprising:

a processing device receiving 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, that are scanned in a fully-differential multi-phase mode;

the processing device generating 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 from 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 visually represents in digital format a fingerprint for the portion of the finger.

4. The method of claim 1 , wherein generating the fingerprint image comprises the processing device generating an excitation matrix that represents polarities of control signals applied to multiplex multiple electrodes of the sensor elements and an output signal matrix that represents the plurality of measurements.

5. The method of claim 1 , wherein the sensor elements of the capacitive fingerprint sensor array include transmit (TX) electrodes, and wherein the processing device generating the fingerprint image comprises:

generating a TX excitation matrix and reducing the TX excitation matrix by one row and one column;

generating an output signal matrix based on the plurality of measurements, and reducing the output signal matrix by one row;

generating a recovered image matrix representing the fingerprint image by concatenating one row of constants to a multiplication product of the output signal matrix and an inverse matrix of the TX excitation matrix.

6. The method of claim 5 , wherein the TX excitation matrix comprises zero-sum excitation vectors, and the method further comprises a sequencer, of the processing device, driving the TX electrodes according to the TX excitation matrix.

7. 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 that comprises zero-sum excitation vectors; and

multiplexing the RX electrodes to one or more differential receivers of the processing device according to the RX excitation matrix;

wherein the processing device generating the fingerprint image comprises:

reducing the RX excitation matrix by one row and one column;

generating an output signal matrix based on the plurality of measurements, and reducing the output signal matrix by one row;

generating a recovered image matrix representing the fingerprint image by concatenating one row of constants to a multiplication product of the output signal matrix and an inverse matrix of the RX excitation matrix.

8. The method of claim 7 , wherein:

multiplexing the RX electrodes further comprises:

connecting the RX electrodes to the one or more differential receivers of the processing device according to the RX excitation matrix, to obtain a first output signal value;

connecting the RX electrodes to the one or more differential receivers of the processing device with signal polarity that is switched with respect to the RX excitation matrix, to obtain a second output signal value; and

the method further comprises computing an output signal value corresponding to the RX electrodes based on the first output signal value and the second output signal value.

9. The method of claim 1 , wherein the sensor elements of the capacitive fingerprint sensor array include transmit (TX) electrodes and receive (RX) electrodes, and wherein the processing device generating the fingerprint image comprises:

generating an RX excitation matrix and reducing the RX excitation matrix by one row and one column;

generating a first output signal matrix based on the plurality of measurements, and reducing the first output signal matrix by one row;

generating a first recovered matrix by concatenating one row of constants to a first multiplication product of the first output signal matrix and an inverse matrix of the RX excitation matrix;

transposing the first recovered matrix to generate a second output signal matrix;

generating a TX excitation matrix and reducing the TX excitation matrix by one row and one column;

reducing the second output signal matrix by one row;

generating a second recovered image matrix representing the fingerprint image by concatenating one row of constants to a second multiplication product of the second output signal matrix and an inverse matrix of the TX excitation matrix.

10. The method of claim 9 , wherein the TX excitation matrix comprises zero-sum excitation vectors and the RX excitation matrix comprises zero-sum excitation vectors, and wherein the method further comprises:

a sequencer, of the processing device, 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.

11. The method of claim 1 , wherein the processing device generating the fingerprint image comprises:

generating an excitation matrix based on a pseudorandom sequence and an autocorrelation function;

generating an output signal matrix based on the plurality of measurements;

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 excitation matrix; and

applying baseline compensation based on the recovered image matrix.

12. A device comprising:

a sequencer configured to control scanning of a capacitive fingerprint sensor array in a fully-differential multi-phase mode;

a differential receiver configured to receive a plurality of measurement signals from the capacitive fingerprint sensor array, the plurality of measurement signals being representative of a portion of a finger on the capacitive fingerprint sensor array; and

a deconvolution engine configured to generate a fingerprint image for the portion of the finger based on the plurality of measurements.

13. The device of claim 12 , wherein the sequencer comprises:

a transmit (TX) control circuit configured to control multiplexing of drive signals to multiple TX electrodes of the capacitive fingerprint sensor array; and

a receive (RX) control circuit configured to control multiplexing of output signals from multiple RX electrodes of the capacitive fingerprint sensor array to the differential receiver.

14. The device of claim 12 , wherein the differential receiver comprises:

a differential amplifier configured to receive the plurality of measurement signals from receive (RX) electrodes of the capacitive fingerprint sensor array;

a quadrature demodulator coupled to the differential amplifier and configured to generate pairs of phase-shifted signals based on output from the differential amplifier; and

a pair of analog-to-digital converters (ADCs) configured to generate I-component values and Q-component values based on the pairs of phase-shifted signals.

15. The device of claim 12 , further comprising a channel engine coupled to the differential receiver, the channel engine configured at least to: compute digital values corresponding to sensor elements of the capacitive fingerprint sensor array based on outputs from the differential receiver; and store the digital values for use by the deconvolution engine.

16. The device of claim 12 , wherein the deconvolution engine comprises one or more hardware circuits configured to generate an excitation matrix that represents polarities of control signals applied to multiplex multiple electrodes of the capacitive fingerprint sensor array and an output signal matrix that stores digital values corresponding to sensor elements of the capacitive fingerprint sensor array.

17. The device of claim 16 , wherein the one or more hardware circuits of the deconvolution engine are configured at least to:

reduce the excitation matrix by one row and one column;

reduce the output signal matrix by one row;

generate a multiplication product of the output signal matrix and an inverse matrix of the excitation matrix; and

generate a recovered image matrix representing the fingerprint image by concatenating one row of constants to the multiplication product.

18. The device of claim 16 , wherein the one or more hardware circuits of the deconvolution engine are configured at least to:

generate the excitation matrix based on a pseudorandom sequence and an autocorrelation function; 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 excitation matrix.

19. 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:

scan the capacitive fingerprint sensor array in a fully-differential multi-phase mode;

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.

20. The system of claim 19 , wherein the capacitive fingerprint sensor array comprises multiple electrodes disposed at a pitch between 0.05 mm and 0.07 mm.

21. The system of claim 19 , wherein the capacitive fingerprint sensor array comprises:

receive (RX) electrodes;

one or more reference electrodes configured to detect noise;

wherein the one or more reference electrodes have width that is substantially equal to the width of the RX electrodes; and

wherein the one or more reference electrodes are disposed at a smaller pitch than the RX electrodes.

22. The system of claim 19 wherein, to generate the fingerprint image, the processing device is configured at least to:

generate an excitation matrix that represents polarities of control signals applied to multiplex multiple electrodes of the capacitive fingerprint sensor array, and reduce the excitation matrix by one row and one column;

generate an output signal matrix that represents the plurality of measurements, and reduce the output signal matrix by one row; and

generate a recovered image matrix representing the fingerprint image by concatenating one row of constants to a multiplication product of the output signal matrix and an inverse matrix of the excitation matrix.