Abstract: A multi-stage apparatus has an input which is coupled to an output by way of a plurality of first stages. The stages are sequentially coupled together to form a chain. A spare stage, which is substantially identical to at least a selected one of said first stages is also provided. The apparatus also includes programmable logic means arranged to uncouple said selected first stage from said chain and to couple said spare stage into said chain such that the input remains coupled to the output by the same number of stages. In this way a redundancy scheme for the multi-stage apparatus is implemented.