A MULTIPLE INPUT CIRCUIT

摘要

A circuit comprises a first circuit portion (52) controllable by first and second inputs, and a second circuit portion (54) for generating the second input. The first circuit portion (52) has first operating characteristics when the second input (invPn) is provided as control input, and second operating characteristics when the second input (invPn) is not provided as control input. The second circuit portion (54) is adapted to cease functioning through ageing before the end of the lifetime of the first circuit portion (52) thereby to switch the first circuit portion from the first to the second operating characteristics. This circuit uses the failure of a portion of the circuit which generates at least one input control signal, so as to change the overall circuit characteristics as the circuit ages. This approach enables the circuit to be operated with first characteristics which are suitable when the circuit has not aged significantly, and to be operated with second characteristics which are suitable when the circuit has aged and is nearer the end of its life.