RECOVERY AND SYNCHRONIZATION DETECTOR FOR QPSK CARRIER WAVE

摘要

PURPOSE:To detect stable synchronization even for fluctuation of a detection signal level by adopting constitution such that a reference voltage tracking the fluctuation of the level of a detection signal is generated and the reference voltage is compared with E<4> cos<4>phi components. CONSTITUTION:An input QPSK (quadruple phase modulation) signal is detected by detectors 1, 2 by using in-phase/orthogonal recovered carriers and the harmonic component is eliminated from the output by low-pass filters 3, 4. The detected signal component is multiplied by a multiplier 8, and its output is squared by a square device 14. The squared output signal becomes E<4> at the time of synchronization by a low-pass filter 16 and E<4>/2 at asynchronication (phi=0 deg.) (phi=0-2pi). The output of the low-pass filter 3 or the level E of the detection signal inputted to a level detector 18 is detected. The output is inputted to a threshold value setting device 19. The threshold value setting device has a function to obtain an output 3/4E<4> with respect to the input E. Thus, the threhold value follows up the fluctuation of the detection level and is controlled to be a median between the input to the voltage comparator at the time of synchronization and the input voltage to the voltage comparator at the time of asynchronization.