波形发生器

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为了给FFT产生输入信号，写了一个信号发生器，用于产生特定频率的方波、三角波、正弦波与余弦波。时钟固定为10M，输出假定为一个12位的DA，三角波、正弦与余弦使用dds生成。

源文件如下：

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company:
// Engineer: longrejoy
//
// Create Date: 2017/04/24 01:12:29
// Design Name:
// Module Name: signal_gen
// Project Name:
// Target Devices:
// Tool Versions:
// Description:
//
// Dependencies:
//
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
//
//////////////////////////////////////////////////////////////////////////////////

module signal_gen(
input clk, //clock,fixed to 10MHz pls
input [23:0] freq, //[23:0] target frquence in Hz between 1 and 5M for square,1 ang 2.5M for triangle,312.5KHz for sin and cos
output signal_square, //signal of square
output [11:0] signal_dds, //signal of triangle ,sin or cos
input [1:0] sel, //[1:0] wave form, 00->sin, 01->cos, 10->triangle, 11->square
input rstn //reset, low level reset the module
);

reg signal_square_reg;
reg [23:0] f_count; //counter for clk
reg [23:0] count_over;
reg [11:0] signal_dds_reg;
reg [11:0] dds_triangle [3:0];
reg [11:0] dds_sin_cos [31:0];
reg [4:0] i;

assign signal_square = signal_square_reg;
assign signal_dds = signal_dds_reg;

always @ (posedge clk or negedge rstn)
begin
if (!rstn)
begin
signal_square_reg <= 1'b0;
signal_dds_reg <= 12'b0;
f_count <= 24'b0;
if (sel == 2'b01)
i <= 5'd24;
else
i <= 5'b0;
case (sel)
2'b00,2'b01://sin and cos
begin
dds_sin_cos [0 ] <= 12'h7FF;
dds_sin_cos [1 ] <= 12'h98E;
dds_sin_cos [2 ] <= 12'hB0E;
dds_sin_cos [3 ] <= 12'hC70;
dds_sin_cos [4 ] <= 12'hDA7;
dds_sin_cos [5 ] <= 12'hEA5;
dds_sin_cos [6 ] <= 12'hF63;
dds_sin_cos [7 ] <= 12'hFD7;
dds_sin_cos [8 ] <= 12'hFFF;
dds_sin_cos [9 ] <= 12'hFD7;
dds_sin_cos [10] <= 12'hF63;
dds_sin_cos [11] <= 12'hEA5;
dds_sin_cos [12] <= 12'hDA7;
dds_sin_cos [13] <= 12'hC70;
dds_sin_cos [14] <= 12'hB0E;
dds_sin_cos [15] <= 12'h98E;
dds_sin_cos [16] <= 12'h7FF;
dds_sin_cos [17] <= 12'h66F;
dds_sin_cos [18] <= 12'h4EF;
dds_sin_cos [19] <= 12'h38D;
dds_sin_cos [20] <= 12'h256;
dds_sin_cos [21] <= 12'h158;
dds_sin_cos [22] <= 12'h9A ;
dds_sin_cos [23] <= 12'h26 ;
dds_sin_cos [24] <= 12'h0 ;
dds_sin_cos [25] <= 12'h26 ;
dds_sin_cos [26] <= 12'h9A ;
dds_sin_cos [27] <= 12'h158;
dds_sin_cos [28] <= 12'h256;
dds_sin_cos [29] <= 12'h38D;
dds_sin_cos [30] <= 12'h4EF;
dds_sin_cos [31] <= 12'h66F;
count_over <= 24'd312500 / freq - 1'b1;
end
2'b10://triangle
begin
dds_triangle[0] <= 12'h7FF;
dds_triangle[1] <= 12'hFFE;
dds_triangle[2] <= 12'h7FF;
dds_triangle[3] <= 12'h0;
count_over <= 24'd2500000 / freq - 1'b1;
end
2'b11://square
count_over <= 24'd5000000 / freq - 1'b1;
default:count_over <= 24'd5000000 / freq - 1'b1;
endcase
end
else
begin
case (sel)
2'b00://sin
begin
f_count <= f_count + 1'b1;
if (f_count == count_over)
begin
if (i == 5'd31)
i <= 5'd0;
else
i <= i + 1'b1;
signal_dds_reg <= dds_sin_cos[i];
f_count <= 24'b0;
end
end
2'b01://cos
begin
f_count <= f_count + 1'b1;
if (f_count == count_over)
begin
if (i == 5'd31)
i <= 5'd0;
else
i <= i + 1'b1;
signal_dds_reg <= dds_sin_cos[i];
f_count <= 24'b0;
end
end
2'b10://triangle
begin
f_count <= f_count + 1'b1;
if (f_count == count_over)
begin
if (i == 5'd3)
i <= 5'd0;
else
i <= i + 1'b1;
signal_dds_reg <= dds_triangle[i];
f_count <= 24'b0;
end
end
2'b11://square
begin
f_count <= f_count + 1'b1;
if (f_count == count_over)
begin
signal_square_reg <= ~signal_square_reg;
f_count <= 24'd0;
end
end
default:
begin
signal_square_reg <= 1'bz;
end
endcase
end
end

endmodule

testbench如下：

仿真结果如下：

注意：

if (i == 5'd31)
i <= 5'd0;
else
i <= i + 1'b1;

这边一定要这么写，不能写成

i <= i + 1'b1;

if (i == 5'd32)
i <= 5'd0;

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