Altera Corporation 7–43
September 2004 Stratix Device Handbook, Volume 2
Implementing High Performance DSP Functions in Stratix & Stratix GX Devices
The DSP block in Figure 7–24 is configured in multiply and add mode.
The three external adders are implemented in logic elements and
therefore are not part of the DSP block. Therefore, for an 18-bit input, each
biquad requires half a DSP block and three logic element adders. The gain
factor can be compensated for at the end of the filtering stage and is not
shown in this simple example. More complex, higher order Butterworth
filters can be realized by cascading several biquads together, as in the IIR
example. Figure 7–25 below shows a 4th order Butterworth filter using
two cascaded biquads in a single DSP block.
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