| 摘要 |
PURPOSE:To compensate a low-pass filter at a pre-stage or a post-stage by connecting an all pass filter having the 1st order transfer function and an all pass filter having the 2nd order transfer function in cascade so as to utilize the group delay characteristic. CONSTITUTION:The 1st all pass filter APC1 receives an input IN via a voltage follower and has the 1st order transfer function comprising a capacitor C11 and a resistor R13. The 2nd all pass filter APC2 has a band pass section as shown in alternate long and two short dashes line. As a result, the 1st all pass filter APC1 has a group delay characteristic where the gain at the low frequency region is increased and the 2nd all pass filter APC2 has a group delay characteristic where the gain has a peak at a middle frequency, and the entire characteristic is a characteristic where the gain is slightly decreased at a high frequency. Since a low-pass filter has a group delay characteristic where the gain is increased at a high frequency, the group delay characteristic is compensated by connecting the all pass filters in this way. |
