Designing PWM in Verilog and SystemVerilog

Pulse-width modulation (PWM) is a technique used in digital circuits to control the amount of power delivered to a load by varying the pulse width of a periodic signal. PWM is commonly used in applications such as motor control, power converters, and LED dimming. In this tutorial, we will discuss how to design PWM in Verilog and SystemVerilog.

Overview of Pulse-Width Modulation

Pulse-width modulation involves generating a periodic signal, typically a square wave, whose duty cycle is modulated to achieve the desired output. The duty cycle is the percentage of the signal that is high (or on) during one period. By varying the duty cycle of the signal, the average power delivered to the load can be controlled.

The PWM signal can be generated using a digital counter and a comparator. The counter generates a periodic signal whose frequency is determined by an external clock. The comparator compares the value of the counter with a reference value and generates a PWM signal whose duty cycle is proportional to the difference between the counter value and the reference value.

Designing PWM in Verilog and SystemVerilog

The following code shows an example implementation of PWM in Verilog and SystemVerilog:

module PWM #(
  parameter DataWidth = 8
) (
  input  logic                 clk,
  input  logic                 rstN,
  input  logic [DataWidth-1:0] threshold,
  output logic                 pwm
);

  logic [DataWidth-1:0] counter, counterNext;
  logic pwmNext;

  always_comb begin
    counterNext = counter + 1;

    if (counter >= threshold) begin
      pwmNext = 1;
    end
    else begin
      pwmNext = 0;
    end
  end

  always_ff @(posedge clk or negedge rstN) begin
    if (!rstN) begin
      counter <= 0;
      pwm     <= 0;
    end
    else begin
      counter <= counterNext;
      pwm     <= pwmNext;
    end
  end

endmodule

The PWM module has four ports: clk, rstN, threshold, and pwm. The clk port is the clock input, the rstN port is the asynchronous reset input (active low), the threshold port is the input that sets the threshold value of the PWM signal, and the pwm port is the output PWM signal.

The counter signal is a digital counter that generates the periodic signal. The counterNext signal is the next value of the counter, calculated using the always_comb block. The pwmNext signal is the next value of the PWM signal, also calculated using the always_comb block.

When the reset signal rstN is low, the counter is reset to zero and the PWM signal is set to low. When the clock signal clk is high, the counter is incremented by one. If the counter value is greater than or equal to the threshold value, the PWM signal is high. Otherwise, the PWM signal is low.

Conclusion

In this tutorial, we discussed how to design a pulse-width modulation (PWM) circuit in Verilog and SystemVerilog using a simplified digital counter and a comparator. Experiment with different threshold values and clock frequencies to achieve the desired output. With a little creativity and ingenuity, you can leverage the power of PWM to solve a wide range of problems in the digital world.