| 摘要 |
PURPOSE:To provide a digital demodulation circuit provided with a PLL loop capable of performing pull-in even when oscillation frequency deviation by the temperature drift of a voltage controlled oscillator (VCO) exists. CONSTITUTION:An input modulated wave is detected by two synchronous detectors 3, 4 by oscillation signals with phases different by 90 deg. mutually from the voltage controlled oscillator(VCO) 1, and multivalue identification decision is applied to a detection signal, and it is outputted as reproducing(demodulated) data output. Also, the PLL loop which performs phase locking by controlling the voltage J controlled oscillator according to an error signal when the arrangement of the detection signal is shifted from a normal position is provided. Also, a synchronism decision circuit 12 which detects whether or not the above synchronism is taken, a voltage sweep circuit 13 which outputs a sawtooth voltage only when no synchronism is taken according to a decision result from the synchronism decision circuit, and an adder 14 which adds the sawtooth voltage from the voltage sweep circuit on the error signal are provided. |
