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Owning Palette: Fixed-Point VIs

Installed With: Adaptive Filter Toolkit

Configures the settings of a fixed-point adaptive filter and simulates the performance of this filter. You also can save the fixed-point adaptive filter settings to an XML file. After you place this Express VI on the block diagram, double-click this Express VI to display the configuration dialog box.

After you determine the fixed-point settings, you can use these settings to generate LabVIEW FPGA code for the fixed-point adaptive filter.

Examples

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
Algorithm Settings	Specifies the algorithm settings for the floating-point adaptive filter. This Express VI supports only the standard least mean squares (LMS) algorithm. You can choose from the following options: Filter length—Specifies the filter length of the adaptive filter. The value must be greater than or equal to 2. The default is 128. Step size—Specifies the step size of the adaptive filter. The value must be greater than zero. The default is 0.00999832.
Fixed-Point Configuration	Specifies the settings that you use to simulate a fixed-point adaptive filter. This section contains the following options: x(n) word length—Specifies the word length of the fixed-point input signal x(n). The valid value range is [16, 32]. The default is 24. x(n) integer word length—Specifies the integer word length of the fixed-point input signal x(n). The default is 1. x(n) minimum—Returns the minimum value of the fixed-point input signal x(n). x(n) maximum—Returns the maximum value of the fixed-point input signal x(n). x(n) desired delta—Returns the increment between numbers of the fixed-point input signal x(n). d(n) word length—Specifies the word length of the fixed-point input signal d(n). The valid value range is [16, 32]. The default is 24. d(n) integer word length—Specifies the integer word length of the fixed-point input signal d(n). The default is 1. d(n) minimum—Returns the minimum value of the fixed-point input signal d(n). d(n) maximum—Returns the maximum value of the fixed-point input signal d(n). d(n) desired delta—Returns the increment between numbers of the fixed-point input signal d(n). w(n) word length—Specifies the word length of the adaptive filter coefficients w(n). Valid values include 16 and 24. The default is 24. w(n) integer word length—Specifies the integer word length of the adaptive filter coefficients w(n). The default is 1. w(n) minimum—Returns the minimum value of the adaptive filter coefficients w(n). w(n) maximum—Returns the maximum value of the adaptive filter coefficients w(n). w(n) desired delta—Returns the increment between numbers of the adaptive filter coefficients w(n). step size word length—Specifies the word length of the step size. LabVIEW sets this value to 16. step size integer word length—Specifies the integer word length of the step size. The default is –2. step size minimum—Returns the minimum value of the step size. step size maximum—Returns the maximum value of the step size. step size desired delta—Returns the increment between numbers of the step size.
Save FXP Settings	Saves the fixed-point settings to an XML file. You can use the AFT Load Fixed-Point Settings VI to load the fixed-point settings from the XML file.

Block Diagram Inputs

Parameter	Description
reset?	Specifies whether to reset the adaptive filter coefficients to zeroes. The default is FALSE.
x(n)	Specifies the fixed-point input signal x(n) to the fixed-point adaptive filter. If you specify a floating-point input signal, this Express VI converts the signal into a fixed-point signal automatically.
d(n)	Specifies the fixed-point input signal d(n) to the fixed-point adaptive filter. If you specify a floating-point input signal, this Express VI converts the signal into a fixed-point signal automatically.
step size	Specifies the step size value for the fixed-point adaptive filter. If the value is zero, this VI processes the input signal without updating the coefficients of the adaptive filter. If the value is greater than zero, this VI uses this value as the step size to update the coefficients of the adaptive filter. This value takes precedence over the step size value that you specify for the Step size dialog box option.
error in (no error)	Describes error conditions that occur before this VI or function runs.

Block Diagram Outputs

Parameter	Description
fixed-point settings	Returns the fixed-point adaptive filter settings that you can save to a file in XML format.
y(n)	Returns the fixed-point output signal y(n) from the fixed-point adaptive filter.
e(n)	Returns the fixed-point error signal, which is the difference between d(n) and y(n).
coefficients	Returns the coefficients of the fixed-point adaptive filter.
error out	Contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces.
simulation information	Returns information about the fixed-point simulation. coefficients overflow—Indicates whether the filter coefficients overflow when you use the fixed-point adaptive filter to process a signal. statistical information—Returns the maximum and minimum values of the filter coefficients. You can use this information to determine appropriate fixed-point settings and to avoid coefficients overflows.

Examples

Refer to the following VIs for examples of using the AFT Simulate Fixed-Point FIR LMS VI:

• Explore Finite Precision Effects VI: labview\examples\Adaptive Filters\Getting Started
• Simulate Fixed-Point LMS Adaptive Filter VI: labview\examples\Adaptive Filters\Getting Started\Simulate Fixed-Point LMS Adaptive Filter