Current-mode approaches to implementing hybrid analogue/digital Viterbi decoders

The add-compare-select (ACS) unit plays a key role in the complexity and speed of a Viterbi decoder. When this unit is realised using analogue circuit design techniques there is a substantial reduction in the number of transistors required compared to digital realisations. In addition, the use of analogue circuit design techniques can result in faster and less power dissipative Viterbi realisations. This paper describes a CMOS high-speed current-mode ACS circuit for use in R=1/n hybrid analogue/digital Viterbi decoders. Unlike previous analogue ACS designs, our proposed approach uses switched current techniques, and since no MOS capacitors are required, the decoder can be realised using an economical single-poly CMOS process