| 摘要 |
A serial Viterbi decoder having a chainback cache is provided for use in a mobile telephone. The decoder includes a branch error metric block, an add-compare-select unit, and a chainback block including a chainback RAM, a full chainback cache and chainback controller circuitry. The chainback cache caches decision bits from previous process cycles such that full chainback operations need not always be performed. The chainback cache is configured to cache on all reads. With the chainback cache, significant savings in power consumption and processing time may be achieved with only a relatively modest increase in the amount of circuitry required. A full chainback cache need not provided. Rather, the chainback block instead includes an L+1 bit RAM, an updown counter and a shift register configured to emulate a chainback cache or an L bit shift register is employed instead of the combination of the L+1 bit RAM and updown counter. The chainback block may be configured to perform only one chainback read or several reads in each process cycle. The chainback block may be configured to perform chainback operations based on (a) through (b) reads where the cache is accessed for each read after (a) reads have been done until (b) reads have been performed or a match is obtained. The chainback block may be configured to perform chainback operations over multiple process cycles rather than only a single process cycle.
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