Adaptive Fir Filter - Freescale Semiconductor DSP56311 User Manual

10.3.6.3 Adaptive FIR Filter

An adaptive FIR filter is represented in Figure 10-8. The goal of the FIR filter is to adjust the
filter coefficients so that the output, F(n), becomes as close as possible to the desired signal,
R(n)—that is, E(n) -> 0.
D(n)
The adaptive FIR filter typically comprises four stages, which are performed for each input
sample at time n:
Stage 1. The FIR filter output value is calculated for the EFCOP FIR session according to
this equation:
where H (i) are the filter coefficients at time n, D(n) is the input signal and F(n) is the
n
filter output at time n. This stage requires N MAC operations, calculated by the EFCOP
FMAC unit.
Stage 2. The core calculates the error signal, E(n), in software according to the following
equation:
where R(n) is the desired signal at time n. This stage requires a single arithmetic operation.
Stage 3. The core calculates the weight multiplier, Ke(n), in software according to the
following equation:
Freescale Semiconductor
Adaptive
FIR Filter
Filter Update
Figure 10-8. Adaptive FIR Filter
N 1 –
∑
F n ( ) i ( )D n i –
= H
n
i = 0
E n ( ) R n ( ) F n ( )
= –
K e (n) = K * E(n)
DSP56311 Reference Manual, Rev. 2
R(n)
F(n)
E(n)
( )
EFCOP Operation
10-25