A digitiser includes a grid of conductors having excitation conductors and detection conductors. Excitation circuitry applies excitation signals to selected excitation conductors; measurement circuitry obtains measurements from selected detection conductors; and processing circuitry processes measurements obtained by the measurement circuitry to detect one or more objects positioned adjacent the grid of conductors. The excitation circuitry may be arranged to operate in a cyclic manner to select each of the excitation conductors during an excitation cycle, wherein an excitation cycle includes a sequence of excitation intervals during each of which a different pair of neighboring excitation conductors is selected by the excitation circuitry and to which complementary excitation signals are applied. The excitation circuitry is arranged to polarity modulate each excitation signal using a polarity control signal so that the polarity of the excitation signal applied to a selected conductor changes during a time that the excitation conductor is selected.