| 摘要 |
PURPOSE:To eliminate the influence of variation in input signal by attaining synchronous drawing-in at a high speed by making a modem vary the coefficient of a digital filter in accordance with the use mode of a timing signal extraction circuit. CONSTITUTION:An input signal is A/D-converted 6 and the led into BPF1, whose output is supplied to PLL2, a sampling pulse from which is supplied to A/D converter 6. Then, BPF1 uses tank circuit 1-0 of relatively-high Q or tank circuit 1-1 of relatively-low Q by switching to store information equivalent to each tank circuit, thereby varying the coefficient of filter 1 in accordance with the use mode. Therefore, a demodulation carrier and discrimination timing pulse can be generated at a high speed without being influenced by variation in input signal. |
