Hi,
I am modelling a polyphase decimation filter in Simulink. In literature there are 2 variant implementations:
- with a commutator
- with extra delay elements and decimators
Slide 25 shows block diagram with commutator and slide 24 without in below presentation:
The attached PolyphaseDecimation2.slx is the version without commutator that gives correct results.
In the attached PolyphaseDecimation.slx I try to simulate the commutator variant. But there is a huge difference between normal filter followed by decimation versus my polyphase implementation. The sine generator makes frames of 4 samples and with a demux I unpack such a frame to four values. Let's calculate the first output value. For the full filter this is the value input(0)*h(0) that will be selected by the decimator as the delay elements are initialized with zeros. The next 3 values coming out of the filter will be discarded. For my filter it is input(0)*h(0)+input(1)*h(1)+input(2)*h(2)+input(3)*h(3). This is clearly different and this is because the input(1:3) are directly used without a delay element.
So probably my interpretation of a polyphase decimator with commutator is not correct? Or are the two variants really different?
Kind regards, Bert
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