Vivado中FFT9.1 IP核的使用(4)——SCALE_SCH缩放设置

本文介绍了Vivado中FFT9.1 IP核的SCALE_SCH设置,用于控制FFT过程的缩放。SCALE_SCH与FFT的阶段数和长度相关,每个阶段可设置不同的移位位数,实现0-8倍的缩放。在对线性调频信号的仿真中,验证了SCALE_SCH的配置,包括不缩放和4倍缩放两种情况,结果与分析一致。

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Vivado中FFT9.1 IP核的使用(3)——线性调频信号FFT的基础上,对SCALE_SCH进行测试

1、SCALE_SCH介绍

SCALE_SCH对FFT过程的缩放进行设置:

  • SCALE_SCH对FFT变换各阶段的缩放进行设置,长度与FFT方式和变换长度有关,比如基2FFT,1024点,对应阶段数为10;
  • 每阶段使用两位进行设置,可以设置为0-1-2-3,对应移位位数,反映在缩放倍数上实际为:0-2-4-8倍;
  • SCALE_SCH从高到低,分别对应FFT最后阶段到初始阶段;

2、仿真

对线性调频信号进行FFT时,IP配置情况如下:

SCALE_SCH位数=阶段数*2=20与分析一致

分别按照不缩放、缩放4倍两种情况进行仿真:

对应输出为:

不缩放:

### Xilinx FFT IP Core SCALE_SCH Parameter Configuration and Function In the context of designing with Xilinx FFT IP cores, configuring the `SCALE_SCH` parameter is crucial to prevent overflow during Fast Fourier Transform (FFT) operations. The `SCALE_SCH`, or scale schedule, determines how much data should be scaled down at each stage of the FFT process by specifying a right shift operation on bits[^1]. This mechanism helps maintain numerical stability throughout the transform stages. The scaling factor for every stage can be set through the configuration interface provided by the FFT IP block. It&#39;s important that sufficient scaling occurs per stage; otherwise, there may still be an occurrence of overflow which could lead to unusable results due to data wrapping around beyond representable values. For precise control over this behavior within designs using Vivado tools, designers must carefully define the width and format required for the `scaling_sch` field as described in documentation such as PG109 document covering details about these parameters across different versions including C/Mex models and System Generator blocks. A practical approach involves testing various settings under controlled conditions similar to those outlined when working specifically with version 9.1 of the FFT IP core where linear frequency modulated signals were analyzed alongside adjustments made via SCALE_SCH configurations[^2]. #### Example Code Demonstrating Scale Schedule Application To illustrate setting up a custom scale schedule programmatically: ```vhdl entity fft_example is port ( clk : in std_logic; resetn : in std_logic; start : in std_logic; done : out std_logic; config_in : out unsigned(7 downto 0); ... ); end entity; architecture Behavioral of fft_example is begin process(clk) variable scale_schedule : integer_vector := (others => 0); -- Initialize all stages without scaling initially. begin if rising_edge(clk) then if resetn = &#39;0&#39; then -- Reset logic here... elsif start = &#39;1&#39; then -- Apply specific scaling factors based on application needs: scale_schedule(0) := 1; -- Stage 1 has one bit shifted right scale_schedule(1) := 2; -- Stage 2 shifts two bits right -- Assign configured schedule into output register connected to FFT IP Config Interface config_in <= to_unsigned(scale_schedule_to_integer(scale_schedule), config_in&#39;length); -- Additional processing after setup... end if; end if; end process; end architecture; ``` --related questions-- 1. How does insufficient scaling affect the accuracy of FFT computations? 2. What are some best practices for determining optimal scaling schedules? 3. Can you explain more about handling overflow prevention strategies besides adjusting SCALE_SCH? 4. In what scenarios would it be necessary to modify default scaling behaviors? 5. Are there any performance trade-offs associated with applying aggressive scaling?
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