VHDL Code for Ramp Wave Generation Using DAC

This article provides VHDL code for generating a ramp wave using a Digital-to-Analog Converter (DAC).

VHDL Code

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_unsigned.all;

entity sawwave is
    port(
        clk, rst : in std_logic;
        dac_out : out std_logic_vector(7 downto 0)
    );
end sawwave;

architecture Behavioral of sawwave is
    signal counter : std_logic_vector(7 downto 0);
    signal div : std_logic_vector(3 downto 0);
    signal clkdiv : std_logic;
begin
    process(clk)
    begin
        if (rising_edge(clk)) then
            div <= div + '1';
        end if;
    end process;

    clkdiv <= div(3);

    process(clkdiv)
    begin
        if rst = '1' then
            counter <= "00000000";
        elsif (rising_edge(clkdiv)) then
            counter <= counter + 1;
        end if;
    end process;

    dac_out <= counter;

end behavioral;

Explanation

The VHDL code defines an entity called sawwave which takes a clock (clk) and reset (rst) signal as input and outputs an 8-bit vector dac_out which represents the ramp wave.

• Clock Divider: The code includes a clock divider to slow down the increment of the counter. This is implemented using the div signal. The clkdiv signal is derived from div(3), effectively dividing the input clock frequency by 16.

• Counter: The counter signal is an 8-bit register that increments on the rising edge of clkdiv. When reset (rst = ‘1’), the counter is initialized to “00000000”.

• DAC Output: The value of the counter is directly assigned to the dac_out port. As the counter increments, the output value increases linearly, generating the ramp wave. The DAC would then convert this digital value to an analog voltage.