注：本设计的参数为：D=2，R=5，N=3；时钟频率为50mhz，输入信号为有符号8位，根据公式bmax=bin+N*log（2，R*D）；可以得到bmax=18；
1，cic抽取滤波器原理
网上资料一大堆，不说了。重点在于传递函数，以及各个部分的结构。
2，simulink仿真
模型图
频谱仪显示结果
3，cic滤波器verilog 代码
module cic_dec(clk,rst_n,datain,dataout);
input clk,rst_n;
input [7:0] datain;
output [7:0] dataout;
reg [17:0] data_buff;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
data_buff<=0;
else
data_buff<={{10{datain[7]}},datain};
end
reg [17:0] integ1_result;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
integ1_result<=0;
else
integ1_result<=data_buff+integ1_result;
end
reg [17:0] integ2_result;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
integ2_result<=0;
else
integ2_result<=integ1_result+integ2_result;
end
reg [17:0] integ3_result;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
integ3_result<=0;
else
integ3_result<=integ2_result+integ3_result;
end
//integrator end
//decimation start
reg dec_flag;
reg [17:0] dec_result;
reg [2:0] cnt1;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
cnt1<=0;
else if(cnt1==3‘d4)
cnt1<=0;
else
cnt1<=cnt1+1‘b1;
end
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
dec_result<=0;
else if(cnt1==3‘d4)
dec_result<=integ3_result;
end
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
dec_flag<=1‘b0;
else if(cnt1==3‘d4)
dec_flag<=1‘b1;
else
dec_flag<=1‘b0;
end
//decimation end
// comb filter begin
reg [2:0] cnt2;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
cnt2<=0;
else if(dec_flag)
cnt2<=0;
else
cnt2<=cnt2+1‘b1;
end
reg [17:0] comb1_delay1;
reg [17:0] comb1_delay2;
reg [17:0] comb1_result;
[email protected](posedge clk or negedge rst_n)//first comb
begin
if(!rst_n)
begin
comb1_delay1<=0;
comb1_delay2<=0;
end
else if(cnt2==3‘d3)
begin
comb1_delay1<=dec_result;
comb1_delay2<=comb1_delay1;
end
end
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
comb1_result<=0;
else if(dec_flag)
comb1_result<=dec_result-comb1_delay2;
end
reg [17:0] comb2_delay1;
reg [17:0] comb2_delay2;
reg [17:0] comb2_result;
[email protected](posedge clk or negedge rst_n)//second comb
begin
if(!rst_n)
begin
comb2_delay1<=0;
comb2_delay2<=0;
end
else if(cnt2==3‘d3)
begin
comb2_delay1<=comb1_result;
comb2_delay2<=comb2_delay1;
end
end
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
comb2_result<=0;
else if(dec_flag)
comb2_result<=comb1_result-comb2_delay2;
end
reg [17:0] comb3_delay1;
reg [17:0] comb3_delay2;
reg [17:0] comb3_result;
[email protected](posedge clk or negedge rst_n)//third comb
begin
if(!rst_n)
begin
comb3_delay1<=0;
comb3_delay2<=0;
end
else if(cnt2==3‘d3)
begin
comb3_delay1<=comb2_result;
comb3_delay2<=comb3_delay1;
end
end
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
comb3_result<=0;
else if(dec_flag)
comb3_result<=comb2_result-comb3_delay2;
end
reg [7:0] dataout_buff;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
dataout_buff<=0;
else
dataout_buff<=(comb3_result[17:0]+{!comb3_result[17],{9{comb3_result[17]}}})>>10;
end
assign dataout=dataout_buff;
endmodule
4，matlab产生正弦波形文件采样频率50m，正弦频率1m
0=1e6;
fs=50e6;
N=fs/f0;
n=0:N-1;
t=n/fs;
width=8;
sinwave=sin(2*pi*f0*t);
sindata = round(sinwave .* (2^(width-1) - 1));
for i=1:N
if(sindata(i)<0)
sindata(i)=2^width+sindata(i);
else
sindata(i)=sindata(i);
end
end
fid=fopen(‘sindata.txt‘,‘a‘);
for i=1:N
fprintf(fid,‘%x \n‘,sindata(i));
i=i+1;
end
fclose(fid);
5，verilog读取波形文件产生正弦波
module sin_gen(clk,rst_n,sin_out);
input clk,rst_n;
output [7:0] sin_out;
parameter N = 50;
reg [7:0] mem[0:N-1];
initial
begin
$readmemh("sindata.txt",mem);
end
reg [7:0] sin_out_buff;
reg [5:0] i;
[email protected](posedge clk or negedge rst_n)
begin
if(!rst_n)
begin
sin_out_buff<=0;
i<=6‘d0;
end
else
begin
sin_out_buff<=mem[i];
if(i==6‘d49)
i<=6‘d0;
else
i<=i+1‘b1;
end
end
assign sin_out=sin_out_buff;
endmodule
6， testbench
`timescale 1ns/1ps
module testbench();
reg clk,rst_n;
initial
begin
clk=0;
forever #10 clk=~clk;
end
initial
begin
rst_n=0;
#50 rst_n=1‘b1;
end
wire [7:0] sin_out;
sin_gen u0_sin_gen(.clk(clk),.rst_n(rst_n),.sin_out(sin_out));
wire [7:0] data_out;
cic_dec u0_cic_dec(.clk(clk),.rst_n(rst_n),.datain(sin_out),.dataout(data_out));
reg [10:0] cnt;
[email protected](posedge clk or negedge rst_n )
begin
if(!rst_n)
cnt<=0;
else if(cnt==11‘d1024)
cnt<=cnt;
else
cnt<=cnt+1‘b1;
end
integer fid;
initial
begin
fid=$fopen("dataout.txt","a");
end
[email protected](posedge clk )
begin
$fwrite(fid,"%x \n",data_out);
end
[email protected](posedge clk)
begin
if(cnt==11‘d1024)
begin
$fclose(fid);
$stop;
end
end
endmodule
7，modelsim 仿真波形
