[Moved] PWM to sine wave generator

[psychoticjoe]

Hello,

I am a newbie to verilog and just got a hold of a FPGA Spartan 3E board but now im in need of some help. Of course I have done a lot of searching and reading first. Anyways, the task I am faced with is to use a Look-up table to generate PWM that will be outputted into an RC filter which will convert my PWM to a 60 Hz sinewave. My board runs at 50 MHz. I am not sure how to use the look up table to create the PWM that will eventually become a 60 Hz sine wave.
ANY feedback is greatly appreciated!

Thanks,
Joe

 

[barry]

The basic principal is that, after filtering, a narrow pulsewidth will yield a low voltage and a wide pulse width will yield a high voltage. Your lookup table will be a table of pulse-widths that correspond to the levels of your sinewave. For example, lets say you use a 36 element table. Each element would represent a ten-degree step through the sine wave. Element 0 would correspond to sine(0), element 1 would be sine(10), element 2 would be sine(20), and so on.

 

[psychoticjoe]

The basic principal is that, after filtering, a narrow pulsewidth will yield a low voltage and a wide pulse width will yield a high voltage. Your lookup table will be a table of pulse-widths that correspond to the levels of your sinewave. For example, lets say you use a 36 element table. Each element would represent a ten-degree step through the sine wave. Element 0 would correspond to sine(0), element 1 would be sine(10), element 2 would be sine(20), and so on.

Hello barry,
Thanks for your response, your answer is very helpful. I guess my only issue at this point after make the table is not knowing how to include it in my code. I did a little more reading and saw that the simplest way would be to use a "case" module?
Either way thanks again you rock man!

 

[mnfsoft]

Well the principal to do this is and a sine wave with a triangle or evan a sawtooth signal the result is PWM well there is many types you must be more specific, like:
www.itu.dk/stud/speciale/segmentering/Matlab6p5/help/toolbox/powersys/pwmgenerator.html
https://pcbheaven.com/wikipages/PWM_Modulation/
https://www.learningelectronics.net/circuits/pwm-dimmermotor-speed-controller.html
...etc.

 

[psychoticjoe]

mnfsoft, the second link you provides comes in very handy and is a visual representation of what barry was trying to tell. I have a pretty good idea of what my output from the board needs to look like but im still not fully sure on how to code it to get this:





For a 36-element table between 0-360 degrees I calculated these numbers:
0, 43, 86, 125, 161, 192, 217, 235, 246, 250, 246, 235, 217, 192, 161, 125, 86, 43, 0, -43, -86, -125, -161, -192, -217, -235, -246, -250, -246, -235, -217, -192, -161, -125, -86, -43

How can I put these into xilinx verilog code using the "case" compare way?
Knowing that my clock default input is 50 MHz what should I do with my clock divider?

Thanks for the input!

 

[barry]

I don't speak Verilog, but I'd first offset your table by 255 so that all the numbers are positive (you can't have a negative pulse width). Then you're going to have to generate a 60x36=2160Hz clock (60 Hz output, 36 samples per cycle). This clock would increment a counter that generates the index into your table. Voila!