A Multi-Level QAM Demodulator LSI with Wideband Carrier Recovery and Dual Equalizing Mode

A 4-/16-/64-/256-QAM demodulator LSI with an all-digital carrier-recovery loop including a novel phase detector and a fractionally-/ symbol-spaced equalizer is described. The phase detector, deciding the transmitted symbol from received signal power, detects the phase error up to ±45° and enables the loop to internally eliminate the ±80 KHz carrier-frequency offset. The fractionally-spaced equalizer is implemented at the same clock rate as the symbol-spaced equalizer by only increasing the selectors and flip-flops, though the former theoretically requires a two times faster operation than the latter. An LSI operating at a symbol rate up to 8 MBaud is successfully implemented.