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Fir Compiler II and User control

Honored Contributor II

Hi everyone, 


I'm trying to implement a 5/4 interpolator (from 80 MHz to 100 MHz). I have designed my filter with Matlab and I have already scaled the coefficients to integer in order to get a gain that is a factor of 2 (in my case 2^17). 


However, Fir Compiler II scaled my coefficients to different values. Why is that? Does it assume that we cannot design filter on our own? I use Matlab to design my filters and also to perform my quantization analysis. and I would expect Altera to accept my filter as-is unless I ask it to.  


In fir Compiler 1, we have to option not to scale the coefficients, but it doesn't support fractional interpolation. I would have to implement my filter in 2 parts (interpolator then decimator) which would be pretty inefficient. 


Does anyone have a solution or a workaround for my problem? 


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Honored Contributor II

i have an "enhancement request" in to Altera on this very problem. i think the easiest work around is a post-filter gain adjustment