LF43168
DEVICES INCORPORATED
Dual 8-Tap FIR Filter
F
IGURE
5.
D
ECIMATING
, E
VEN
-S
YMMETRIC
C
OEFFICIENT
F
ILTER
C
ONFIGURATIONS
LIFO A
LIFO A
N = Delay Length (Decimation Factor)
MUX
N = Delay Length (Decimation Factor)
DEMUX
MUX
N
N
N
N
N
N
LIFO B
DATA IN
N
N
N
DATA IN
N
N
N
Delay Stage N – 1 Output
A
B+A
B
A
B+A
B
A
B+A
B
A
B+A
B
A
B+A
B
A
B+A
B
A
B+A
B
A
B+A
B
COEF 0
COEF 1
COEF 2
COEF 3
COEF 0
COEF 1
COEF 2
COEF 3
EVEN-TAP FILTER
ODD-TAP FILTER
F
IGURE
6.
O
DD
-S
YMMETRIC
C
OEFFICIENT
F
ILTER
C
ONFIGURATIONS
LIFO A
N = Delay Length (Decimation Factor)
MUX
LIFO B
N
N
N
DATA IN
DATA IN
N
N
N
A
B–A
B
A
B–A
B
A
B–A
B
A
B–A
B
A
B–A
B
A
B–A
B
A
B–A
B
A
B–A
B
COEF 0
COEF 0
COEF 1
COEF 1
COEF 2
COEF 2
COEF 3
COEF 3
EVEN-TAP FILTER (NO DECIMATION)
DECIMATING, EVEN-TAP FILTER
Figure 5 shows the two possible
configurations when the device is
programmed as a decimating, even-
symmetric coefficient filter. The delay
length of the decimation registers will
be equal to the decimation factor that
the device is programmed for. Since
only four coefficients (effectively
eight) can be sent to the filter multipli-
ers on a clock cycle, it may be neces-
sary (depending on the coefficient set)
to change the coefficients fed to the
multipliers on different CLK cycles for
filters with more than eight taps. Note
that for the odd-tap filter, the middle
coefficient of the coefficient set must
be divided by two to get the correct
result.
Odd-Symmetric Coefficient Filters
Figure 6 shows the two possible
configurations when the device is
programmed for odd-symmetric
coefficients. Note that odd-tap, odd-
symmetric coefficient filters are not
possible.
Video Imaging Products
8
03/28/2000–LDS.43168-H
LIFO B
DEMUX
DEMUX
LOGIC [ LOGIC DEVICES INCORPORATED ]
