Method and apparatus for interfacing with a touch sensor

An apparatus configured for reading a touch sensor having columns and rows forming a row-column grid, the apparatus comprising:

• first multiplexing circuitry configured to:
• apply a set of column input signals simultaneously to respective column inputs of the touch sensor, each column input signal being an analog signal at a respective frequency;
• and
• apply a set of row input signals simultaneously to respective row inputs of the touch sensor, each row input signal being an analog signal at a respective frequency;
• second multiplexing circuitry configured to:
• combine column output signals taken from respective column outputs of the touch sensor to form a combined column signal, each column output signal corresponding to a respective one of the column input signals but altered in amplitude in dependence on whether the touch sensor is being touched in a vertical screen region corresponding to the respective column of the touch sensor;
• and
• combine row output signals taken from respective row outputs of the touch sensor to form a combined row signal, each row output signal corresponding to a respective one of the row input signals but altered in amplitude in dependence on whether the touch sensor is being touched in a horizontal screen region corresponding to the respective row of the touch sensor;
• and
• processing circuitry configured to:
• perform a frequency-domain transform on digitized samples of the combined column signal and on digitized samples of the combined row signal, to obtain, respectively, a set of column values that depend on the amplitudes of the corresponding column output signals in the combined column signal, and a set of row values that depend on the amplitude of the corresponding row output signals in the combined row signal;
• and
• detect a touch input to the touch sensor by evaluating the column values and the row values.