A high-speed, high-sensitivity demodulation sensor usable for e.g. time-of-flight application uses a back side illuminated (BSI) image sensor chip, in which the photo-generated charges are first transferred to a demodulation area, from which the charges are then sampled and stored on at least one specific storage node. The storage node is electrically isolated from the sensitive area. Such a pixel might find its use specifically in 3D time-of-flight imaging given its improvements in sensitivity because the presented invention allows to design pixel with up to 100% fill factor and enables charge detection even if the charge generation by the photon occurs deep in the silicon substrate.