| 摘要 |
PURPOSE:To improve the reliability of the demodulating operation by using a differential signal corresponding to the phase comparison signal between a 2n-phase PSK signal and a voltage controlled oscillator signal and a signal, which is obtained by shifting the level of its inverted signal, as a signal to be controlled and a control signal respectively to resolve the DC offset and generating a demodulated subcarrier signal having an accurate phase difference from an input signal. CONSTITUTION:Output signals a1 and a2 from phase detectors 12 and 13 are supplied to differential amplifiers 4A and 4B. The signal a1 is converted to a differential signals a11 (non-inverted signal) and a12 (inverted signal), and they are supplied to not only terminals 6AA and 6AB of an analog switch 6A but also an analog switch 6B through a level shifting circuit 5A as control signals b11 and b12. The signal a2 as well is subjected to the similar processing. Signals G2 and G1 outputted from switches 6A and 6B are added by an adding circuit 7 to become a phase error signal G3, and this signal G3 has the noise eliminated by an LPF 15, and the oscillation phase is so controlled by a voltage controlled oscillator VCO 16 that the amplitude of the signal G3 is in the zero level, and thus, the phase difference between the carrier signal of the 2n-phase PSK signal and the subcarrier signal is determined by an initial condition and is stabilized. |
