| 摘要 |
PURPOSE:To prevent the disturbance of a signal waveform by correcting the group delay characteristics of a low pass filter LPF before A/D or D/A conversion. CONSTITUTION:The group delays of the digital all pass filters DAPF 10 and 11 provided after an A/D converter 2 and before a D/A converter 4 respectively can be set optionally. For instance, the analog LPF 1 and 5 have the constant frequency and group delay characteristics and these group delay characteristics are not flat at a point near the cut-off frequency. Under such conditions, the levels of the DAPF 10 and 11 are set constant to the frequency together with their group delay times are small at the point near the cut-off frequency unlike the LPF 1 and 5. The DAPF 10 corrects the group delay of the signal passed through the LPF 1; while the DAPF 11 corrects previously the group delay of the signal passing through the LPF 5 respectively. Thus the disturbance of a signal waveform is prevented.
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