1. A analog to digital converter, comprising: an input for receiving an input signal to be digitised; a first converter core for performing a first part of an analog to digital conversion, and for outputting a first digital result; a first residue generator for generating a first residue as a difference between the input signal and the first digital result; a second converter core for performing a second part of the analog to digital conversion by converting the first residue; wherein at least one of the first and second converter cores comprises at least three analog to digital conversion engines and a controller for controlling the operation of the engines such that the engines collaborate to perform a successive approximation search.