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仿真已通过
module dpll(reset,clk,signal_in,signal_out,syn);
parameter para_K=4;
parameter para_N=16;
input reset;
input clk;
input signal_in;
output signal_out;
output syn;
reg signal_out;
reg dpout;
reg delclk;
reg addclk;
reg add_del_clkout;
reg [7:0]up_down_cnt;
reg [2:0]cnt8;
reg [8:0]cnt_N;
reg syn;
reg dpout_delay;
reg [8:0]cnt_dpout_high;
reg [8:0]cnt_dpout_low; /******phase detector*****/
always@(signal_in or signal_out)
begin
dpout<=signal_in^signal_out;
end /******synchronization establish detector*****/
always@(posedge clk or negedge reset)
begin
if(!reset) dpout_delay<='b0;
else dpout_delay<=dpout;
end
always@(posedge clk or negedge reset)
begin
if(!reset)
begin
cnt_dpout_high<='b0; cnt_dpout_low<='b0;
end
else if(dpout)
if(dpout_delay==0) cnt_dpout_high<='b0;
else
if(cnt_dpout_high==8'b11111111) cnt_dpout_high<='b0;
else cnt_dpout_high<=cnt_dpout_high+1;
else if(!dpout)
if(dpout_delay==1) cnt_dpout_low<='b0;
else
if(cnt_dpout_low==8'b11111111) cnt_dpout_low<='b0;
else cnt_dpout_low<=cnt_dpout_low+1;
end
always@(posedge clk or negedge reset)
begin
if(!reset) syn<='b0;
else if((dpout&&!dpout_delay)||(!dpout&&dpout_delay))
if(cnt_dpout_high[8:0]-cnt_dpout_low[8:0]<=4||cnt_dpout_low[8:0]-cnt_dpout_high[8:0]<=4) syn<='b1;
else syn<='b0;
end /****up down couter with mod=K****/
always@(posedge clk or negedge reset)
begin
if(!reset)
begin
delclk<='b0;
addclk<='b0;
up_down_cnt<='b00000000;
end
else
begin
if(!dpout)
begin
delclk<='b0;
if(up_down_cnt==para_K-1)
begin
up_down_cnt<='b00000000;
addclk<='b0;
end
else
begin
up_down_cnt<=up_down_cnt+1;
addclk<='b0;
end
end
else
begin
addclk<='b0;
if(up_down_cnt=='b0)
begin
up_down_cnt<=para_K-1;
delclk<='b0;
end
else
if(up_down_cnt==1)
begin
delclk<='b1;
up_down_cnt<=up_down_cnt-1;
end
else
up_down_cnt<=up_down_cnt-1;
end
end
end /******add and delete clk*****/
always@(posedge clk or negedge reset)
begin
if(!reset)
begin
cnt8<='b000;
end
else
begin
if(cnt8=='b111)
begin
cnt8<='b000;
end
else
if(addclk&&!syn)
begin
cnt8<=cnt8+2;
end
else
if(delclk&&!syn)
cnt8<=cnt8;
else
cnt8<=cnt8+1;
end
end
always@(cnt8 or reset)
begin
if(!reset)
add_del_clkout<='b0;
else
add_del_clkout<=cnt8[2];
end /******counter with mod=N******/
always@(posedge add_del_clkout or negedge reset)
begin
if(!reset)
begin
cnt_N<='b0000;
signal_out<='b0;
end
else
begin
if(cnt_N==para_N-1)
begin
cnt_N<='b0000;
signal_out<='b0;
end
else
if(cnt_N==(para_N-1)/2)
begin
signal_out<='b1;
cnt_N<=cnt_N+1;
end
else
cnt_N<=cnt_N+1;
end
end
endmodule DPLL由 鉴相器、 模K加减计数器、脉冲加减电路、同步建立侦察电路、模N分频器构成.
整个系统的中心频率(即signal_in和signal_out的码速率的2倍)为clk/8/N. 模K加减计数器的K值决定DPLL的精度和同步建立时间,K越大,则同步建立时间长,同步精度高.反之则短,低.
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