Interpolated Filter - 7.2 English - PG149

FIR Compiler LogiCORE IP Product Guide ( PG149)
Document ID
PG149
Release Date
2025-06-11
Version
7.2 English

A previous section explained that an IFIR filter is similar to a conventional FIR, but with the unit delay operator replaced by k-1 units of delay. k is referred to as the zero-packing factor. One way to realize this substitution is by the insertion of k-1 zeros between the coefficient values of a prototype filter. When specifying an IFIR architecture, the full set of prototype coefficients is supplied in the coefficient file, without the zeros implied by the zero-packing factor. The zero-packing factor is defined through the filter user interface. For example, consider the filter coefficient data in the .coe file shown in the following figure.

Figure 1. Prototype Coefficient Data for IFIR Example

If a zero-packing factor of k=2 is specified, the equivalent filter impulse response is shown in the following figure.

Figure 2. Equivalent IFIR Impulse Response for the Coefficient Data Shown in the preceding figure (Prototype Coefficient Data for IFIR Example) with a Zero-packing Factor k=2

If the zero-packing factor is changed to k=3, the impulse response is as shown in the following figure.

Figure 3. Equivalent IFIR Impulse Response for the Coefficient Data Shown in the preceding figure (Prototype Coefficient Data for IFIR Example) with a Zero-packing Factor k=3

These examples use a symmetrical prototype impulse response; this is not a restriction of the filter core. The prototype filter coefficient set can be symmetrical, non-symmetrical, or negative-symmetric.