This Figure shows the polyphase decimation filter option which implements the computationally efficient M -to-1 polyphase decimating filter.
A set of
N
prototype filter coefficients
is mapped to the
M
polyphase subfilters
according to
Equation 3-1
.
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
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
rate is
where
is the sample rate of the input data stream
.
Observe that each of the polyphase segments is operating at the low output sample rate
(compared to the high input sample rate
), and a total of
operations is performed per output point.