An electron gun for a color cathode ray tube efficiently modulates magnetic field of a velocity modulation coil. The clock circuit provides a first differential clock signal and the control circuit generates a control signal based at least in part on the frequency of the first differential clock signal. The touch panel is connected to a sensing module having a plurality of shift registers connected in series. The invention has particular application as an equalisation element in the field of fibre optic communications networks so as to counteract dispersion and other complex signal impairments .