Subversion Repositories pwm_with_dithering

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-- Company:              Aboa Space Research Oy (ASRO)

-- Engineer:             Tero Säntti

-- 

-- Create Date:    15:02:39 01/27/2021 

-- Design Name:          PWM verifier

-- Module Name:    pwm_to_voltage - Behavioral 

-- Target Devices: None / Simulation ONLY

-- Tool versions:  None / non-specific

-- Description:          Calculate PWM to real voltage. Adjustable R, C and supply 

--                                               voltage. Auto refresh option, in case PWM is halted or keeps 

--                                               '0' or '1' for extended time, also usefull if RC filters are 

--                                               cascaded after this, and require smaller time steps.

--

-- Revision: 

-- Revision 0.01 - File Created

-- Additional Comments: 

--

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.NUMERIC_STD.ALL;

use IEEE.math_real.all;

entity pwm_to_voltage is

    Generic (

                                autorefresh_interval : time;

                                autorefresh_enabled : boolean;

                                supply_voltage : real:=3.3;

                                R : real:=100.0;

                                C : real:=0.0001

                                );

    Port ( pwm : in  STD_LOGIC;

           voltage : out real;

                          frequency : out real

                          );

end pwm_to_voltage;

architecture Behavioral of pwm_to_voltage is

signal cur:real:=0.0;

signal prev_dir:std_logic:='0';

signal auto:std_logic:='0';

begin

-- output mapping:

voltage <= cur;

doit:process(pwm,auto)

variable time_diff:time;

variable real_time_diff_sec:real;

variable last_update:time:= 0 ns;

begin

        time_diff := now - last_update;

        real_time_diff_sec:=(real(time_diff/(1 ps)))/1000000000000.0;

        if prev_dir='0' then

                cur <= cur*((2.71828182845904523536028747135266249775724709369995 ** ((0.0-real_time_diff_sec)/(R*C))));

        else

                cur <= cur + (supply_voltage-cur)*(1.0-(2.71828182845904523536028747135266249775724709369995 ** ((0.0-real_time_diff_sec)/(R*C))));

        end if;

        last_update := now;

        prev_dir <= pwm;

end process;

autorefresh:process

   begin

                if autorefresh_enabled then

                        auto <= '0';

                        wait for autorefresh_interval;

                        auto <= '1';

                        wait for autorefresh_interval;

                else

                        auto <= '0';

                        wait;

                end if;

   end process;

freq_monitor:process(pwm)

variable up_time:time;

begin

if pwm='1' then

        frequency <= 1000000000000.0 / ((now - up_time)/1.0 ps);

        up_time := now;

end if;

end process;

end Behavioral;