| 摘要 |
PURPOSE:To quickly realize synchronism acquisition by preventing the malfunction of the phase adjustment control circuit of a demodulator at the time of the asynchronous state. CONSTITUTION:This phase adjustment control circuit is provided with two phase detectors 1A and 1B which take a PSK modulated wave or a multilevel QAM modulated wave as the input and perform the synchronous detection by a reference carrier signal from a VCO 4 and the reference carrier signal which has the phase shifted by 90 deg., a variable phase shifter 5 which controls the orthogonal phase of two reference carriers, two discriminators 2A and 2B which take output signals of detectors 1A and 1B as the input and perform the multilevel discrimination, an APC circuit 3 which subjects the outputs of discriminators 2A and 2B to logical processing to control the output phase of the VCO 4, an AQC circuit 6 which subjects the outputs of dis- criminators 2A and 2B to logical processing to control the variable phase shifter 5 and shifts the phase of the reference carrier by pi/2, and a carrier asynchronous detection circuit 7 which monitors the output signal of the APC circuit 6 and detects step out of the carrier, and a switch circuit 9 is provided between the AQC circuit 6 and the variable phase shifter 5; and when the circuit 7 detects the asynchronous state, the switch circuit 9 supplies a certain voltage to the variable phase shifter 5 by disconnection. |
