It provides functions for both FIR and IIR filters that are highly optimized. The best and most efferent way of implementing a digital filter in an embedded system based on an ARM Cortex-M processor is using the DSP library provided by ARM, the CMSIS-DSP library. In general, we first simulate and tune the frequency response of the desired filter on the PC using tools like SciLab (or Matlab) or online design tools like MicroModeler.Īfter tuning the filter to get the required characteristics, the filter needs to be implemented in C to run on an MCU. There are many different types of filters but the fundamental ones are the FIR and IIR filters. If you appreciated this post, please help us to share it with your friend.Digital Filters are one of the fundamental blocks for digital signal processing, like the analog filters are for analog signal conditioning. ![]() The implementation should be guarantee full speed for the FIR filter.įigure 3 shows RTL viewer of Altera Quartus II for the FIR filter VHLD example code above Figure 3 – FIR Filter Quartus II RTL viewer The VHDL code of the FIR filter can be implemented either in ASIC or in FPGA. The output dynamic of the FIR filter is 10-bit, i.e. The FIR filter is implemented fully pipelined, in fact, there is a registration stage at the output of each multiplication or addition. O_data <= std_logic_vector(r_add_st1(17 downto 8)) Signal r_add_st1 : signed(15+2 downto 0) Type t_add_st0 is array (0 to 1) of signed(15+1 downto 0) Type t_mult is array (0 to 3) of signed(15 downto 0) Type t_coeff is array (0 to 3) of signed(7 downto 0) Type t_data_pipe is array (0 to 3) of signed(7 downto 0) O_data : out std_logic_vector( 9 downto 0)) I_data : in std_logic_vector( 7 downto 0) I_coeff_3 : in std_logic_vector( 7 downto 0) I_coeff_2 : in std_logic_vector( 7 downto 0) I_coeff_1 : in std_logic_vector( 7 downto 0) ![]() I_coeff_0 : in std_logic_vector( 7 downto 0) The VHDL code implements a low pass FIR filter with 4 taps, 8-bit input, 8-bit coefficient. Here below is reported the VHDL code for the FIR filter design of figure 2. 4-taps FIR Filter hardware architecture example The FIR filter design architecture of figure 2 can be easily extended to a length greater than 4. When you perform addition, the number of bit of the result will be incremented by 1. In fact, when you multiply two numbers of N-bit and M-bit the output dynamic of the multiplication result is (N+M)-bits. ![]() ![]() In figure 2, the input x(n) and the coefficient bi are 8-bits signed.Īfter the filter coefficients multiplication, the multiplier output dynamic will be an 8+8=16 bit. Here we want to see how to implement FIR filter architecture in FPGA or ASIC using VHDL.įigure 2 reports an example of 4 taps FIR direct form that can be simply coded in VHDL. Figure 1 – FIR Filter direct form implementation On Wikipedia FIR web-page, you can find further information on FIR design theory. This computation is also known as discrete convolution. If the filter is a direct form FIR filter then is also a coefficient of the filter (see Figure1).
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