Polyphase Decimator - 7.2 English

FIR Compiler (PG149)

Document ID
PG149
Release Date
2022-10-26
Version
7.2 English

This Figure shows the polyphase decimation filter option which implements the computationally efficient M -to-1 polyphase decimating filter.

Figure 3-26: M -to-1 Polyphase Decimating Filter

X-Ref Target - Figure 3-26

m_to_1_polyphase_pg34_pg149.jpg

A set of N prototype filter coefficients pg149-designing00176_pg149.jpg is mapped to the M polyphase subfilters pg149-designing00178_pg149.jpg according to Equation 3-1 .

pg149-designing00180_pg149.jpg

The polyphase segments are accessed by delivering the input samples x ( n ) to their inputs using an input commutator which starts at the segment index pg149-designing00182_pg149.jpg and decrements to index 0. After the commutator has executed one cycle and delivered M input samples to the filter, a single output is taken as the summation of the outputs from the polyphase segments. The output sample inset_12_pg149.jpg rate is inset_13_pg149.jpg where inset_14_pg149.jpg is the sample rate of the input data stream pg149-designing00187_pg149.jpg .

Observe that each of the polyphase segments is operating at the low output sample rate pg149-designing00189_pg149.jpg (compared to the high input sample rate inset_17_pg149.jpg ), and a total of inset_18_pg149.jpg operations is performed per output point.