用VHDL做出一个锁相环
时间: 2023-07-01 12:25:01 浏览: 55
锁相环(Phase Locked Loop, PLL)是一种广泛应用于通信、计算机和自动控制领域的电路。它可以将输入信号的相位锁定在参考信号的相位,并输出与参考信号相同频率的新信号。
下面是一个基于VHDL实现的简单锁相环的代码示例:
```vhdl
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
entity PLL is
Port ( CLK_IN : in STD_LOGIC;
CLK_OUT : out STD_LOGIC);
end PLL;
architecture Behavioral of PLL is
signal phase : std_logic_vector(7 downto 0);
signal counter : unsigned(7 downto 0) := (others => '0');
signal phase_diff : std_logic_vector(7 downto 0);
signal phase_diff_reg : std_logic_vector(7 downto 0);
signal phase_diff_delta : std_logic_vector(7 downto 0);
signal phase_diff_delta_reg : std_logic_vector(7 downto 0);
signal phase_diff_delta_delta : std_logic_vector(7 downto 0);
signal phase_diff_delta_delta_reg : std_logic_vector(7 downto 0);
signal phase_diff_delta_delta_delta : std_logic_vector(7 downto 0);
signal phase_diff_delta_delta_delta_reg : std_logic_vector(7 downto 0);
signal feedback : std_logic;
begin
-- Phase detector
process(CLK_IN, counter)
begin
if rising_edge(CLK_IN) then
phase <= phase + 1;
if phase = 255 then
phase <= (others => '0');
end if;
if feedback = '1' then
phase_diff <= std_logic_vector(unsigned(phase) - counter);
else
phase_diff <= std_logic_vector(counter - unsigned(phase));
end if;
end if;
end process;
-- Charge pump
process(CLK_IN)
begin
if rising_edge(CLK_IN) then
if phase_diff /= phase_diff_reg then
phase_diff_delta <= phase_diff - phase_diff_reg;
else
phase_diff_delta <= (others => '0');
end if;
if phase_diff_delta /= phase_diff_delta_reg then
phase_diff_delta_delta <= phase_diff_delta - phase_diff_delta_reg;
else
phase_diff_delta_delta <= (others => '0');
end if;
if phase_diff_delta_delta /= phase_diff_delta_delta_reg then
phase_diff_delta_delta_delta <= phase_diff_delta_delta - phase_diff_delta_delta_reg;
else
phase_diff_delta_delta_delta <= (others => '0');
end if;
if phase_diff_delta_delta_delta /= phase_diff_delta_delta_delta_reg then
CLK_OUT <= not CLK_OUT;
end if;
phase_diff_reg <= phase_diff;
phase_diff_delta_reg <= phase_diff_delta;
phase_diff_delta_delta_reg <= phase_diff_delta_delta;
phase_diff_delta_delta_delta_reg <= phase_diff_delta_delta_delta;
end if;
end process;
-- Divider
process(CLK_OUT)
begin
if rising_edge(CLK_OUT) then
counter <= counter + 1;
if counter = "10000000" then
counter <= (others => '0');
feedback <= not feedback;
end if;
end if;
end process;
end Behavioral;
```
该代码实现了一个简单的锁相环,包括相位检测器、电荷泵、分频器等模块。其中,相位检测器用于比较输入信号和反馈信号之间的相位差,电荷泵用于产生控制电压,分频器用于将输出信号分频。该代码的输入信号为`CLK_IN`,输出信号为`CLK_OUT`。在每个时钟周期内,输入信号的相位会逐渐增加,如果输入信号的相位落后于反馈信号,电荷泵会产生正电压,使分频器的计数器加速;如果输入信号的相位领先于反馈信号,电荷泵会产生负电压,使分频器的计数器减速。当计数器达到设定值时,分频器输出一个时钟信号,作为锁相环的输出信号。