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Altera_Forum's avatar
Altera_Forum
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13 years ago

the quarter sine LUT code

Dear all

I need to get the quarter sine LUT in DDFS (Herewith the MATLAB code that I used)

i=[0:i-1];

x= (i-1)*sin ((pi/2)*i/31));

5 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    --- Quote Start ---

    I need to get the quarter sine LUT

    --- Quote End ---

    Hope you got it :)

    What exactly the question is?
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    According to this equation :

    i=[0:i-1];

    x= (i-1)*sin ((pi/2)*i/i-1)+ 1/2*(i-1));

    The result that I got is not the sine wave shape (the LUT values inverted in minus when it pass the half of (pi/2) range ). herewith the attached sine wave file
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    As far as i know MATLAB uses floating point representation, which is not implemented in HDL by default. Maybe if you give more information (LUT input,output width, precision, what language you use) I could help you out.

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    The Quarter sine wave LUT code for 8 bits:

    i=[0:255];

    x= 255*sin ((pi/2) *i /255);

    y=str(x,8) ;

    but when i used it in DDS simulation , I got no sine wave((note: i applied all the other requirment))
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    There is some error in your sine values but almost correct.

    Try this:

    x = round(255*sin(2*pi*(0:1023)/1024));

    x = x(1:256);

    You should get proper quarter sine from x otherwise tell us what you do with x.

    you can also just use:

    x = round(255*sin(2*pi*(0:255)/1024));