hsp43891 Intersil Corporation, hsp43891 Datasheet - Page 12

• Manufacturer Part Number: hsp43891
• Description: Digital Filter
• Manufacturer: Intersil Corporation

Single DF Configuration
Using a single DF, a filter of length L>8 can be constructed
by processing in L/8 passes, as illustrated in Table 2, for a
16-tap FIR. Each pass is composed of Tp = 7 + L cycles and
computes eight output samples. In pass i, the sample with
indices i*8 to i*8 +(L-1) enter the DIN0-8 inputs. The
coefficients C
seven zeros. As these zeros are entered, the result samples
are output and the accumulators reset. Initial filing of the
pipeline is not shown in this sequence table. Filter outputs
can be put through a FIFO to even out the sample rate.
Extended Coefficient and Data Sample
Word Size
The sample and coefficient word size can be extended by
utilizing several DFs in parallel to get the maximum sample
rate or a single DF with resulting lower sample rates. The
technique is to compute partial products of 9 x 9 and
combine these partial products by shifting and adding to
obtain the final result. The shifting and adding can be
accomplished with external adders (at full speed) or with the
DF’s shift-and-add mechanism contained in its output stage
(at reduced speed).
0
- C
L
- 1 enter the CIN0-8 inputs, followed by
12
HSP43891
Decimation/Resampling
The HSP43891 DF provides a mechanism for decimating by
factors of 2, 3, or 4. From the DF filter cell block diagram
(Figure 1), note the three D registers and two multiplexers in
the coefficient path through the cell. These allow the
coefficients to be delayed by 1, 2, or 3 clocks through the
cell. The sequence table (Table 3) for a decimate-by-two
filter illustrates the technique (internal cell pipelining ignored
for simplicity). Detailed timing for a 30MHz input sample rate,
15MHz output sample rate (i.e., decimate-by-two), 16-tap
FIR filter, including pipelining, is shown in Figure 7. This filter
requires only a single HSP43891 DF.