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NI-DSP Analysis VI Reference Chapter 2
Part 3: NI-DSP Function Reference 2-40 NI-DSP SRM for LabVIEW for Windows
DSP IIR Filter
Performs IIR filtering on the
X input array and reports the
result in Y. It uses the arrays
a and b of sizes sza and szb
respectively in implementing
the linear difference equation
that describes IIR filtering:
k = sza - 1 k = szb-1
y[i] = ∑ a(k) * x(i-k) - ∑ b(k) * y(i-k) i = 0,1 ..... ,n-1
k = 0 k = 1
where:
a is the array of forward coefficients describing an IIR filter (obtained from DSP Butterworth Coefficients
VI for example)
b is the array of feedback coefficients describing an IIR filter (obtained from the same filter design VI)
Notes: b(0) = 1.0 in the above equation.
This VI may be called in a loop to perform filtering on data frames that are part of the same data stream.
At time i = 0, the initial conditions on X (for example, X(1-sza) through X(-1)) are obtained from the array
Initial Conditions on input. At exit (the end of the VI execution), this array holds the final conditions on
X that could be used as the initial conditions for the next DSP IIR Filter VI call if you were to call it in a
loop.
At time i = 0, the initial conditions on Y (for example, Y(1-szb) through Y(-1)) are obtained from the array
Initial Conditions on output. At exit (the end of the VI execution), this array holds the final conditions on
Y that could be used as the initial conditions for the next DSP IIR Filter VI call if you were to call it in a
loop.
X is a DSP Handle Cluster that indicates the memory buffer on the DSP board that contains the input
signal array.
Y in is a DSP Handle Cluster that indicates the memory buffer on the DSP board that will contain the
output array of filtered data.
Initial Conditions on input is a DSP Handle Cluster that indicates the memory buffer on the DSP board
that contains the initial conditions on input at time zero.
Initial Conditions on output is a DSP Handle Cluster that indicates the memory buffer on the DSP
board that contains the initial conditions on output at time zero.
Forward Coefficients is a DSP Handle Cluster that indicates the memory buffer on the DSP board that
contains the forward coefficients of the IIR filter.
Feedback Coefficients is a DSP Handle Cluster that indicates the memory buffer on the DSP board that
contains the feedback coefficients of the IIR filter.