Altera Stratix - Basic IIR Filters; Basic IIR Filter Implementation

7–36 Altera Corporation
Stratix Device Handbook, Volume 2 September 2004
Infinite Impulse Response (IIR) Filters
This cascaded structure rearranges the transfer function. This is shown in
the equation below, where each product term is a second order IIR filter.
If n is odd, the last product term is a first order IIR filter:
Figure 7–21 shows the cascaded structure.
Figure 7–21. Cascaded IIR Filter
Basic IIR Filters
In this section, the basic IIR filter is implemented using cascaded second
order blocks or biquads in the direct form II structure.
Basic IIR FIlter Implementation
Multiplier blocks, adders and delay elements can implement a basic IIR
filter. The Stratix architecture lends itself to IIR filters because of its
embedded DSP blocks, which can easily be configured to perform these
operations. The altmult_add megafunction can be used to implement
the multiplier-adder mode in the DSP blocks. Figure 7–22 shows the
implementation of an individual biquad using Stratix and Stratix GX DSP
blocks.
Hz() C
a
0k
a
1k
z
1–
a+
2k
z
2–
+
1b
1k
z
1–
b
2k
z
2–
++
----------------------------------------------------
k1=
n1+()2⁄
∏
× CH
k
z()
k1=
n1+()2⁄
∏
×==
x(n)
y(n
)
H (z)
1
H (z)
k
H (z)
n
C