Pulse code modulation passband filter and method for obtaining multiple filter passbands

摘要

A 1st frequency reduction circuit of a filter of the invention downsamples the sampling rate of a signal source to a predetermined value to obtain a 1st PCM stream, a 1st frequency raising circuit raises the sampling rate of the 1st PCM stream to be the same as that of the signal source, a 1st delay circuit delays a stream of the signal source, such that its phase is the same as that of the 1st PCM stream, a 1st adder subtracts the frequency raised 1st PCM steam from the delayed stream of the signal source to obtain a passband 1, a j-th frequency reduction circuit downsamples the sampling rate of a (j−1)-th PCM stream to a predetermined value to obtain a j-th PCM stream, wherein 2≤j≤n, a j-th frequency raising circuit raises the sampling rate of the j-th PCM stream to be the same as that of the (j−1)-th PCM stream, a j-th delay circuit delays the (j−1)-th PCM stream, such that its phase is the same as that of the j-th PCM stream, a j-th adder subtracts the frequency raised j-th PCM stream from the delayed (j−1)-th PCM stream to obtain a passband j, and when j=n, the j-th PCM stream is a passband n+1.