Altera FIR Compiler Manuel d'utilisateur télécharger pdf (Page 51)

Chapter 4: Functional Description 4–9

FIR Compiler

Mathematically, when a signal is interpolated, zeros are inserted between data points

and the data is then filtered to remove spectral components that were not present in

the original signal (Figure 4–7).

To decimate a signal, a low-pass filter is applied, which removes spectral components

that will not be present at the low sample rate. After filtering, appropriate sample

values are taken (Figure 4–8).

The FIR Compiler generates interpolation and decimation filters by combining high-

and low-level optimization techniques.

Using the high-level optimization technique, the FIR Compiler processes the data

from a polyphase decomposed filter. The polyphase decomposition breaks a single

filter into several smaller filters, which results in the following:

■ When using an interpolation filter, zero-stuffed data does not need to be

computed; potentially saving resources (Figure 4–9 on page 4–10).

■ When using a decimation filter, output data—which is discarded during

downsampling—is never computed, again potentially saving resources

(Figure 4–10 on page 4–11).

Using the low-level optimization technique, the polyphase decomposed filter is

implemented using a multichannel, multiple coefficient set structure with an

appropriate wrapper.

Figure 4–7. Signal Interpolation

Figure 4–8. Signal Decimation

Input

Data

After

Zero

Stuffing

After

Low-Pass

Filtering

LPF

Input Output

Input

Data

Filtered

Data

Decimated

Data

LPF

Input Output

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Altera FIR Compiler Manuel d'utilisateur Page 51