the quarter sine LUT code

Altera_Forum · ‎10-09-2012

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));

Altera_Forum · ‎10-09-2012

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I need to get the quarter sine LUT

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Hope you got it :)

What exactly the question is?

Altera_Forum · ‎10-10-2012

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 · ‎10-10-2012

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 · ‎10-13-2012

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 · ‎10-13-2012

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));