Multiphase fingerprint sensor layout and construction

A method comprising:

• receiving a first signal on a first receive fingerprint sensing electrode, the first signal representative of a mutual capacitance of a first unit cell comprising the first receive fingerprint sensing electrode;
• receiving a second signal on a second receive fingerprint sensing electrode, the second signal representative of a mutual capacitance of second unit cell comprising the second receive fingerprint sensing electrode;
• combining the first and second signals to create a combined signal, the combined signal representative of a mutual capacitance of the first unit cell without parasitic capacitance from the first receive fingerprint sensing electrode;
• and
• converting the combined signal to a digital value,
• wherein the second unit cell is formed outside a sensing area including the first unit cell, the first unit cell disposed such that the mutual capacitance of the first unit cell is alterable by a conductive object and the second unit cell disposed such that the mutual capacitance of the second unit cell is isolated from the conductive object.

A fingerprint imaging device comprising:

• a sensing array comprising:
• a first plurality of unit cells formed within a sensing area, the first plurality of unit cells disposed such that a capacitance of each unit cell is alterable by a conductive object;
• a second plurality of unit cells formed outside the sensing area, the second plurality of unit cells disposed such that a capacitance of each of the second plurality of unit cells is isolated from the conductive object;
• a capacitance measurement circuit coupled to at least one electrode of each of the first and second pluralities of unit cells, the capacitance measurement circuit for converting a first signal received on the at least one electrode of a first unit cell of the first plurality of unit cells to a digital value representative of a capacitance of the first unit cell, wherein a second signal received on the at least one electrode of the second plurality of unit cells modifies the first signal;
• and
• a processor for evaluating the digital value and constructing an image of a fingerprint therefrom.