500 Mb/s soft output Viterbi decoder

Two 8-state, 7-bit soft output Viterbi decoders matched to an EPR4 channel and a rate-8/9 convolutional code are implemented in 0.18µm CMOS technology. Architectural transformation of the add-compare-select structures and modification of the register exchange allow a high throughput with small area overhead. The 4mm
²
chip has been verified to decode at 500Mb/s with 1.8V supply. These decoders are used with Turbo codes, which have been demonstrated to achieve information rates very close to the Shannon limit.