hsp43168 Intersil Corporation, hsp43168 Datasheet - Page 12

• Manufacturer Part Number: hsp43168
• Description: Dual Fir Filter
• Manufacturer: Intersil Corporation

Example 2. Odd-Tap Even Symmetric
Filter Example
The HSP43168 may be configured as two independent
7-tap symmetric filters with a Functional Block Diagram
shown in Figure 8. Again, this example shows data flow
through one of the two FIR cells. As in the 8-tap filter
example, the HSP43168 implements the filtering operation
by summing data samples sharing a common coefficient
prior to multiplication by that coefficient. However, for odd
length filters the pre-addition requires that the center
coefficient be scaled by 1/2.
FIGURE 8. USING HSP43168 AS TWO INDEPENDENT FILTERS
FIGURE 7B. DATA FLOW AS DATA SAMPLE 8 IS CLOCKED
FIGURE 7C. DATA FLOW AS DATA SAMPLE 9 IS CLOCKED
FIGURE 7. DATA FLOW DIAGRAMS FOR 8-TAP SYMMETRIC
INA0-9
INB0-9
A
B
C0
C0
8
9
(X9 + X2)C0 + (X8 + X3)C1 + (X7 + X4)C2 + (X6 + X5)C3
A
B
(X8 + X1)C0 + (X7 + X2)C1 + (X6+X3)C2 + (X5 + X4)C3
+
+
FILTER
7-TAP EVEN SYMMETRIC
7-TAP EVEN SYMMETRIC
INTO THE FEED FORWARD STAGE
INTO THE FEED FORWARD STAGE
C1
C1
1
2
7
8
FIR A
FIR B
+
+
HSP43168
C2
C2
2
3
6
+
7
+
12
+
+
C3
C3
M
U
X
3
4
5
6
+
+
5
4
OUT9-27
HSP43168
The operation of the FIR cell for odd length filters is better
understood by comparing the data/coefficient alignment in
Figure 9 with the Data Flow Diagrams in Figure 10. The
Block Diagrams in Figure 10 are a simplification of the FIR
cell shown in Figure 1.
For odd length filters, proper data/coefficient alignment is
ensured by routing data entering the last register in the third
forward decimation stage to the Backward Shifting
Registers. In this configuration, the center coefficient must
be scaled by 1/2 to compensate for the summation of the
same data sample from both the Forward and Backward
Shifting Registers.
FIGURE 10A. DATA FLOW AS DATA SAMPLE 6 IS CLOCKED
FIGURE 10B. DATA FLOW AS DATA SAMPLE 7 IS CLOCKED
FIGURE 9. DATA/COEFFICIENT ALIGNMENT FOR 7-TAP
h(n)
x(n)
C0
C0
6
7
(X7 + X1)C0 + (X 6 + X2)C1 + (X5 + X3)C2 + (X4 + X4)C3/2
X9
(X6 + X0)C0 + (X5 + X1)C1 + (X4 + X2)C2 + (X3 + X3)C3/2
+
+
X8
SYMMETRIC FILTER
INTO THE FEED FORWARD STAGE
INTO THE FEED FORWARD STAGE
C1
C1
0
1
5
6
X7
+
+
C0
X6
C2
C2
1
2
4
+
5
+
C1
X5
C2
+
X4
+
C3/2
C3/2
2
3
3
4
C3
X3
C2
X2
+
+
C1
X1
3
7-TAPS
4
C0
X0