Project a Counter with a Dephased Clock.

Altera_Forum · ‎03-13-2014

Hello,

I am working in a Project in a Power Eletronic's laboratory and I am stucked in a part of the project. I am suposed to built a high-frequency PWM to get a high resolution in the convertion and I my only ideia does not work.

To explain what I am doing and what I am supposed to do:

I have a counter that counts the range of 0 to 4095 (12 bits) with a frequency of 100Mhz (using a PLL) utilizing the FPGA DE-0 Nano with a clock of 50MHz. Dividing the value of 100Mhz per 4095, I got a number of ~28k, but I need the value of 3 Mhz in this division, so I need to "multiply" my clock of 100 Mhz. The first action is to make the digital circuit counts in the falling edge of the clock, so I double the count of the counter. The second idea that I had it was develop lots of dephased clocks to put in paralel process, but I couldn't make a variable increment on the multiple process.

  
    process(i_clk)
    begin
    
        if rising_edge(i_clk) then -- normal clock
                acumula <= acumula +1;  -- the variable that will be incremented on the two parallel process
                if acumula = "111111111111" then
                    acumula <= (others => '0');
                end if;
                if acumula = "000000000111" then
                else s_out_2 <= '0';
                end if;
            end if;
    end process;
    process(i_clk_defasado) -- dephased clock
    begin
        if rising_edge(i_clk_defasado) then
            acumula <= acumula +1;
                if acumula = "111111111111" then
                    acumula <= (others => '0');
                end if;
                if acumula = "000000000111" then
                    s_out_2 <= '1';
                else s_out_2 <= '0';
                end if;
        end process;

Help, please! :P

Sorry if I did any language mistake... I am Brazilian!

Altera_Forum · ‎03-13-2014

if I understood you.

you want to divide 100MHz clock into 3MHz.

accumulate 3 modulo 100 i.e:

0+3

3+3

6+3

...

96+3

99+3 => 2

2+3

5+3

...

watch count value if < 50 then output '0' else output '1'

This division is fractional and corrects itself on average

Altera_Forum · ‎03-13-2014

No, I want to multiply the quocient of 100mhz/4095 = 28k to 3MHz. It is if I multiply the input clock to 103 times to supply my PWM correctly. Do you got my main idea?

Altera_Forum · ‎03-13-2014

well I don't get it really. Note also 100MHz/4095 = 24.42Khz not 28KHz, am I right?

you mean multiply 100MHz to 100*103 = ??? too fast

Altera_Forum · ‎03-13-2014

But it looks like you eventually want 3MHz clock rate. So the modulo adder I posted should serve same purpose