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Fixed point with positive scaling doesn't work!

Altera_Forum
Honored Contributor II
787 Views

Adder block with sfix and positive exponents gives incorrect results. I've tried this with MATLAB 15 and DSP builder blocks (not with synthesis), and the results are wrong. See image attached. The first case adds two complex numbers, with positive exponent scaling. The result is WAY OFF by a factor of 2^10!<br> 

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The second and third add the same numbers with zero and -1 exponent scaling, respectively, and the results are correct.<br> 

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It seems like the first case actually multiplies the values by 2^10, but this strange scaling does not happen in the other two cases.<br> 

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Seems like a major problem here. 

http://www.alteraforum.com/forum/attachment.php?attachmentid=10731&stc=1
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