Using the FDATool in Digital Filter Applications - 2022.1 English

Vitis Model Composer User Guide (UG1483)

Document ID
UG1483
Release Date
2022-05-26
Version
2022.1 English

The FDATool block is used to define the filter order and coefficients, and the HDL blocks are used to implement a filter. The Tools library in the HDL Blockset contains the FDATool block.

Figure 1. FDATool Block

A simple Model Composer model below illustrates a standard FIR filter design using the FDATool and digital FIR filter block.

The design uses two sine wave sources which are being added together and passed separately through two low-pass filters.

  • The first filter is the one that could be implemented using the Xilinx HDL blockset. It is a digital low pass filter implemented using the Digital FIR filter block.
  • The second filter is what is referred to as a reference filter. A low pass filter is implemented using a Direct-form FIR structure.

The frequency response of both filters visualized in Spectrum Analyzer block.

Figure 2. Spectrum Analyzer Block

The Xilinx version of the FDAtool can be used to define the coefficients of the low-pass filter to eliminate high-frequency noise. The filter configuration parameters like Response Type, Filter Order, Frequency Specification, and Magnitude Specification can be modified from the Properties Editor of the FDATool as shown below.

Figure 3. Filter Configuration

The Design Filter option at the bottom of the tool window allows you to find out the filter order and observe the Magnitude Response. You can also view the Phase Response, Impulse Response, Coefficients, and more by selecting the appropriate icon at the top-right of the window. You can display the filter coefficients in the MATLABĀ® workspace by typing the following:

>> xlfda_numerator('FDATool')

The following functions help you find the maximum and minimum coefficient values to adequately specify the coefficient width and binary point:

>> max(xlfda_numerator('FDATool'))
>> min(xlfda_numerator('FDATool'))

Now, the filter parameters of the FDATool instance can be associated with the Digital FIR filter instance.

Figure 4. Digital FIR Filter

The Xilinx Filter response can be viewed and compared with the SimulinkĀ® response using the Spectrum Analyzer.

Figure 5. Spectrum Analyzer
Note: The frequency response results of Model Composer (right side), shown above, differs slightly with the original design (left side) due to the quantization and sampling effect inherent when a continuous time system is described in discrete time hardware.

For complete example along with steps to use the FDATool, refer to the Vitis Model Composer Tutorial (UG1498).