High-speed carrier recovery circuit suitable for direct digital QPSK transceivers

Results are presented on a new rapid method proposed for recovering the carrier frequency of M-PSK and M-QAM modulated signals in six-port based direct digital receivers (SPR) using a reverse modulation loop (RML) technique. The method is valid for hardware and software SPR, avoids the use of mixers, except for a phase-locked loop (PLL), and is suitable for both microwave and millimeter-wave frequencies. Simulations of RML performance are presented, that include measured bit error rate (BER) of receiver sub-circuit at 40 Mbps. Measurements are given for two six-port prototypes fabricated in microwave monolithic integrated circuits (MMIC) and microwave integrated circuits (MIC) technologies.