| 摘要 |
The digital part of the bandpass filter consists of the cascade circuit of several part-filters, all of which or a majority of which are second-order IIR filters (7, 8, 10), and contain an FIR filter (10) in one variant, and of an envelope detector (9). At least two of the IIR filters (7, 8) together form a detuning filter. The frequency ranges which are not, or not adequately, filtered out by the detuning filter are filtered out in two variants with the additional IIR and FIR filters. In addition, there is an analog prefilter which filters out the frequency range not yet filtered, nevertheless, and suppresses the mains frequency and strong harmonics of it to such an extent that an inexpensive analog/digital converter is adequate for the digitisation.
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