| 摘要 |
PURPOSE:To obtain an automatic frequency control(AFC) signal independently of a phase of a modulation signal by applying signal processing to a QPSK signal based on two signals being an in-phase component and an orthogonal component delayed and detected. CONSTITUTION:A delay detection means of a delay detection processing circuit 100 converts an inputted QPSK signal into a base frequency band QPSK signal to apply delay detection and outputs two delay detection signals k, l having a relation of orthogonal phase. Then an output means detects a component of a frequency difference from the delay detection signals k, l. In this case, a level of the detection signal (q) is a function of a frequency error independently of the modulation signal. The signal (q) is fed back to a variable frequency oscillator 5 through an integration device 27. Thus, since the AFC signal fed back to the variable frequency oscillator is independent of the modulation signal of the inputted QPSK signal, even when a spectrum deviation takes place in the QPSK signal, stable AFC is applied. |
