| 摘要 |
PURPOSE:To eliminate waveform distortion after FM detection by group delay caused by an analog filter inserted before A/D conversion stage by setting group delay characteristics of an analog filter and a digital filter complementally. CONSTITUTION:FM video signals are supplied to an analog LPF 2 through an input terminal 1, and after extracting necessary band component in the LPF 2, supplied to an A/D converter 4, and outputted digitalized FM video signals are supplied to a digital BPF 6. The digital BPF 6 extracts only component necessary for detecting video signals from A/D conversion output including FM aural signals and supplies to an FM detection circuit 7 of next stage. In such a case, the digital BPF 6 has group delay characteristic complementary to group delay characteristic of the analog LPF 2. By using digital BPF 6 having such group delay characteristic, group delay (phase distortion) caused by the analog LPF 2 before A/D conversion is corrected, and can be supplied to an FM detecting circuit 7 in the state devoid of group delay.
|
