| 摘要 |
An object of the present invention is to provide a digital filter which allows for separately and independently adjusting and designing an intended filter characteristic and a filter characteristic for eliminating noise components. The digital filter is configured to include a main filter section (12), having a transfer function G(z), for applying an intended filter characteristic to an input signal X sampled at a frequency higher than the Nyquist frequency for output; a quantizer section (13) for re-quantizing an output D2 from the main filter section (12) to output an output signal Y; a sub-filter section (14), having an inverse transfer function G -1 (z) from the transfer function G(z) of the main filter section (12), for filtering the output signal Y; a noise shaping section (16) having a transfer function K(z) created by allowing a transfer function W(z) of a low-band rejection filter to be subtracted from 1, the low-band rejection filter having a low-band rejection characteristic in a predetermined frequency band of a noise component including a quantization error Q(z); an addition section (11) for adding the input signal X and an output D5 from the noise shaping section (16) for delivery to the main filter section (12); and a subtracter section (15) for computing the difference between a sum signal D1 and an output D3 from the sub-filter section (14) to supply a differential signal D4 to the noise shaping section (16).
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