| 摘要 |
PURPOSE:To always secure the steady reproduction of the carrier wave by preventing the shift of the stability point of the loop in the period of a small carrier-noise ratio C/N, and thus to reduce the bit error rate for the demodulation data in the coherent detection. CONSTITUTION:Digital phase modulation signal PSK wave (a) which is supplied receives the envelope curve detection through AM detection circuit 18 to become like (b). With a level decision given to signal (b) at sampling control circuit 14, control signal (c) is obtained. Control signal (c) blocks the sampling action of sampling hold circuit SH13 while the C/N is small at the narrow part of the PSK wave, i.e., signal (c) is kept at the L level, and thus the value sampled precedingly is held. As a result, the control voltage supplied to voltage control type oscillator VCO15 features a small fluctuation like (e) even though the output signal of LPF12 varies like (d) due to the noise effect given in the period of a small C/N. |
