Summary: Implementation of a polyphase interpolation filter.
Recall the standard interpolation procedure illustrated in Figure 1.
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Note that this procedure is computationally inefficient because the lowpass filter operates on a sequence that is mostly composed of zeros. Through the use of the Noble identities, it is possible to rearrange the preceding block diagram so that operations on zero-valued samples are avoided.
In order to apply the Noble identity for interpolation, we must
transform
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Applying the Noble identity for interpolation to Figure 3 yields Figure 2. The ladder of upsamplers and delays on the right below accomplishes a form of parallel-to-serial conversion.
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