Carrier recovery device for quadrature amplitude modulation of RC-phase locked loop scheme for fast acqusition time

摘要

PURPOSE: A carrier frequency recovery apparatus for quadrature amplitude modulation in RC-phase locked loop mode with a short acquisition time is provided which reduces the threshold value of the RC-phase locked loop to demodulate the carrier and then increases the threshold value to minutely demodulate it again. CONSTITUTION: A carrier frequency recovery apparatus for quadrature amplitude modulation includes a phase detector(110) for measuring a phase error between an in-phase component signal and quadrature phase component signal transmitted, a loop filter(120) for attenuating the phase error, and a complex absolute value circuit(160) for converting the in-phase component signal and the quadrature phase component signal into complex numbers to obtain their absolute values. The apparatus also has a select signal generator(130) for generating a select signal in response to the phase error, a mode selector(140) for selecting one of a first mode of outputting a first threshold value for roughly demodulating a carrier frequency and a second mode of outputting a second threshold value for minute operation in response to the select signal, a multiplexer(170) for outputting the output of the loop filter only when the absolute values are larger than the output threshold value of the mode selector and outputting zero when they are not, and a voltage controller oscillator(180) for correcting the in-phase component signal and the quadrature phase component signal in response to the output value of the multiplexer.