1. A method of processing a first set of pairs of complementary differential signals representative of a numerical value expressed in a multi-bit thermometer code, said method comprising: processing a first subset of components of the first set of pairs of complementary differential electrical signals in accordance with a first set of Boolean functions to produce a first set of output electrical signal components, and processing a second subset of components of the first set of pairs of complementary differential electrical signals in accordance with a second set of Boolean functions to produce a second set of output electrical signal components, and wherein the first and second subsets and the first and second sets of Boolean functions are such that the first and second sets of output electrical signal components when combined form a second set of pairs of differential electrical signals representative of said numerical value expressed in a second multi-bit code with fewer bits than the multi-bit thermometer code, and wherein the first and second sets of Boolean functions produce complementary results in the second set of pairs of differential electrical signals for all legal thermometer codes but produce non-complementary results in the second set of pairs of differential electrical signals for at least some illegal thermometer codes.