| 摘要 |
PURPOSE:To obtain the band pass characteristic with a steep band pass characteristic with less hardware by interposing a cyclic filter having a low Q band pass characteristic inverse to a trap characteristic between a noncyclic filter taking a low pass characteristic as a major characteristic and a cyclic filter having the steep trap characteristic at the cut off frequency region. CONSTITUTION:The entire characteristic is raised at the pass band frequencies near the cut-off frequency region by adding cyclic filters 12, 13 having a band pass characteristic to relax the boundary characteristic of a noncyclic filter 11. Thus, the bit shift processing is employed for the reduction in the number of order of the cyclic filters 12, 13 and the setting of the coefficient. The post- stage cyclic filter 13 has a steep trap characteristic at the cutoff frequency region. On the other hand, the cyclic filter 12 of the pre-stage has the band pass characteristic inverse to the trap characteristic of the cyclic filter 13 of the post-stage. In such a case, is resonance frequency of the cyclic filter 12 is selected to be equal to the trap frequency of the cyclic filter 13 and its Q is set higher.
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