1. A method for producing a binary code corresponding to a first thermometer code, each bit of said first thermometer code being represented by the state of a separate one of a set of digital signals, the method comprising the steps of: grouping said signals into selected subsets each representing a further thermometer code; converting each said signal subset thermometer code into a corresponding binary code; and summing the binary codes representing each signal subset to produce the binary code corresponding to said first thermometer code.