
7–24
Altera Corporation
Stratix Device Handbook, Volume 2
September 2004
Finite Impulse Response (FIR) Filters
Polyphase Interpolation Filter Implementation Results
Table 7–11 shows the results of the polyphase interpolation filter
implementation in a Stratix device shown in
Figure 7–13.
Polyphase Interpolation Filter Design Example
Download the Interpolation FIR Filter (interpolation_fir.zip) design
example from the Design Examples section of the Altera web site at
www.altera.com.
Polyphase FIR Decimation Filters
A decimation filter can be used to decrease the sample rate. A decimation
filter is efficiently implemented with a polyphase FIR filter. DSP systems
frequently use polyphase filters because they simplify overall system
design and also reduce the number of computations per cycle required of
the hardware. This section first describes decimation filters and then how
to implement them as polyphase filters in Stratix devices. See the
interpolation filters.
Decimation Filter Basics
A decimation filter decreases the output sample rate by a factor of D
through keeping only every D-th input sample. Consequently, the
samples at the output of the decimation filter are separated by D
× T
s=
D
/fs, where Ts and fs are the sample period and sample frequency of the
original signal, respectively.
Figure 7–14 shows the concept of signal
decimation.
The signal needs to be low pass filtered before downsampling can begin
in order to avoid the reflections of the original spectrum from being
aliased back into the output signal.
Table 7–11. Polyphase Interpolation Filter Implementation Results
Part
EP1S10F780
Utilization
Lcell: 3/10570 (<1%)
DSP Block 9-bit elements: 8/48 (17%)
Memory bits: 288/920448 (<1%)
Performance
(1)
This refers to the performance of the DSP blocks, as well as the output clock rate.
The input rate is 60 MSPS, clocked in at 60MHz.