Creation of virtual intersection points on a touchscreen to permit static, non swiping fingerprint user authentication

A method of operating a touch-sensitive grid of transmit and receive electrodes comprising:

• for each particular scan in a sequence of scans,
• applying a first excitation signal to a first transmit electrode;
• applying a second excitation signal to a second transmit electrode, the second excitation signal scaled by an amplitude factor associated with the particular scan in the sequence of scans;
• such that an electric field generated adjacent the array in turn depends upon both the first excitation signal and the second excitation signal;
• detecting a first response signal from a first receive electrode;
• detecting a second response signal from a second receive electrode;
• and
• combining the first and second response signals to provide a corresponding combined response signal for each particular scan,
• such that the resulting sequence of combined response signals resulting from the is electric fields generated as a result of the sequence of scans corresponds to responses received at a series of virtual intersection points located between at least two physical intersection points of the grid.