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Jean-Baptiste Rolland 3 years ago
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Source/FilteringFunctions/arm_biquad_cascade_df2T_f64.c
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/** /**
@defgroup BiquadCascadeDF2T Biquad Cascade IIR Filters Using a Direct Form II Transposed Structure @defgroup BiquadCascadeDF2T Biquad Cascade IIR Filters Using a Direct Form II Transposed Structure
This set of functions implements arbitrary order recursive (IIR) filters using a transposed direct form II structure. This set of functions implements arbitrary order recursive (IIR) filters using a transposed direct form II structure.
The filters are implemented as a cascade of second order Biquad sections. The filters are implemented as a cascade of second order Biquad sections.
These functions provide a slight memory savings as compared to the direct form I Biquad filter functions. These functions provide a slight memory savings as compared to the direct form I Biquad filter functions.
Only floating-point data is supported. Only floating-point data is supported.
This function operate on blocks of input and output data and each call to the function This function operate on blocks of input and output data and each call to the function
processes <code>blockSize</code> samples through the filter. processes <code>blockSize</code> samples through the filter.
<code>pSrc</code> points to the array of input data and <code>pSrc</code> points to the array of input data and
<code>pDst</code> points to the array of output data. <code>pDst</code> points to the array of output data.
Both arrays contain <code>blockSize</code> values. Both arrays contain <code>blockSize</code> values.
@par Algorithm @par Algorithm
Each Biquad stage implements a second order filter using the difference equation: Each Biquad stage implements a second order filter using the difference equation:
<pre> <pre>
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The transposed Direct Form II structure, on the other hand, requires a wide dynamic range for the state variables <code>d1</code> and <code>d2</code>. The transposed Direct Form II structure, on the other hand, requires a wide dynamic range for the state variables <code>d1</code> and <code>d2</code>.
Because of this, the CMSIS library only has a floating-point version of the Direct Form II Biquad. Because of this, the CMSIS library only has a floating-point version of the Direct Form II Biquad.
The advantage of the Direct Form II Biquad is that it requires half the number of state variables, 2 rather than 4, per Biquad stage. The advantage of the Direct Form II Biquad is that it requires half the number of state variables, 2 rather than 4, per Biquad stage.
@par Instance Structure @par Instance Structure
The coefficients and state variables for a filter are stored together in an instance data structure. The coefficients and state variables for a filter are stored together in an instance data structure.
A separate instance structure must be defined for each filter. A separate instance structure must be defined for each filter.
Coefficient arrays may be shared among several instances while state variable arrays cannot be shared. Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.
@par Init Functions @par Init Functions
There is also an associated initialization function. There is also an associated initialization function.
The initialization function performs following operations: The initialization function performs following operations:

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