Transmit 2 bits of 1MHz (modulation)

Hi,

PWM is much easier than other types of modulation. As you said you will map the 2 bit input to the 3 voltage levels using a simple mux. I assume your input clk is 100MHz then you can produce 25MHz at 25%, 50% and 75% duty cycle using simple counter. Then you switch out the generated clocks as per incoming levels.

I am not that sure about demodulation plan and would like to learn from your work. I assume it will be straight forward if the Tx/Rx clocks are synchronised

I suggest the following process to generate the duty cycles(code not tested)

signal count : integer range 0 to 3 := 0;

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process(reset,clkin) -- 100MHz clkin

begin

if(reset = '1')then

count <= 0;

clkout <= '0';

clk1 <= '0'; -- 25MHz, 25% duty

clk2 <= '0'; -- 25MHz, 50% duty

clk3 <= '0'; -- 25MHz, 75% duty

elsif(rising_edge(clkin))then

count <= count + 1;

case count is

when 0 => clk1 <= '1'; clk2 <= '1'; clk3 <= '1';

when 1 => clk1 <= '0'; clk2 <= '1'; clk3 <= '1';

when 2 => clk1 <= '0'; clk2 <= '0'; clk3 <= '1';

when 3 => clk1 <= '0'; clk2 <= '0'; clk3 <= '0';

when others => null;

end case;

case input_level is

when "00" => clkout <= clk1;

when "01" => clkout <= clk2;

when "10" => clkout <= clk3;

when others => null;

end case;

end if;

end process;