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Fractional mode of altera_fir_compiler_ii

Ono
Beginner
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altera_fir_compiler_ii version 18.0
What is the configuration in Fractional mode?
Is "Up sampling→LPF→Down sampling"?

In the Frequency Response (Magnitude) graph of the cofficients tag,
It is displayed as an FS value after Down sampling.

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SengKok_L_Intel
Moderator
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Hi,


When you choose fractional rate, it allows you to configure both interpolation factor and decimation factor for either up or down sampling conversion.


Regards -SK


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Ono
Beginner
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For example, Interpolation 3
If the decimation is 2,

LPF processing is performed before decimation (Up sampling → LPF → Down sampling) and after (Up sampling → Down sampling → LPF).

Which will you be?

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SengKok_L_Intel
Moderator
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The decimation is deleting the sample, where the Interpolation is adding zero between the sample.

The LPF only processing once, and the output will be deleting the sample (as per decimation factor), and then adding zero (as per interpolation factor).

You may perform the RTL simulation to understand the behaviour in detail. 


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SengKok_L_Intel
Moderator
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