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Altera_Forum
Honored Contributor I
1,488 Views

CORDIC vs. Matlab results

Hello, 

I am using Altera CORDIC for ATan2 and SinCos functions. I am applying the same test vectors to the CORDIC ATan2 and SinCos functions testbench and to the ATan2 and SinCos Matlab Models. I see about 10% of samples don’t match between CORDIC functions and Matlab outputs. For both Matlab and CORDIC I use the same S18,17 inputs for ATan2; S11,8 output for ATan2; S11,8 input for SinCos; S10,8 output for SinCos. 

Any idea why it happens? 

Thanks, 

Mike
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3 Replies
Altera_Forum
Honored Contributor I
50 Views

cordic gives approximate result and its accuracy depends on number of internal iterations(rotations).

Altera_Forum
Honored Contributor I
50 Views

 

--- Quote Start ---  

cordic gives approximate result and its accuracy depends on number of internal iterations(rotations). 

--- Quote End ---  

 

Kaz, 

Thanks! 

Could you please recommend application notes or/and user manuals I could learn more how to increase CORDIC accuracy?
Altera_Forum
Honored Contributor I
50 Views

 

--- Quote Start ---  

Kaz, 

Thanks! 

Could you please recommend application notes or/and user manuals I could learn more how to increase CORDIC accuracy? 

--- Quote End ---  

 

 

I understand you are using Altera's cordic but can't find any link to its manual.  

 

Xilinx has cordic ip and its manual at: 

 

http://www.xilinx.com/support/documentation/ip_documentation/cordic/v6_0/pg105-cordic.pdf 

 

This should give you some idea about available settings. 

 

there is also a cordic ip at opencores. It is not difficult to write your own targeting specific trigonometric function.  

 

The following pdf provides a good basis: 

 

http://www.ee.ic.ac.uk/pcheung/teaching/ee3_dsd/crdcsrvy.pdf
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