| 摘要 |
PURPOSE:To attain stable demodulation even when fluctuation of a received carrier frequency is large by switching two phase error signals depending on kinds of modulated data and feeding back the selected signal to a frequency conversion local oscillator. CONSTITUTION:An input modulation wave Vin is converted into an intermediate frequency by a mixer 3, the phase of a modulation output Vif and of an output VR from a reference oscillator 17 are compared directly by a phase detector 20 to detect a phase error signal Ve2 and the circuit is synchronized in a short period by feeding back the signal to the local oscillator 2 via a loop filter 21. Since the synchronization is finished and the signal is demodulated while being switched into a Costas loop just before a substantial data is transmitted, the IF signals is subject to phase synchronization in a short period even for a carrier suppression double band signal having a large frequency fluctuation and transmitted in a burst form. |
