Honored Contributor
Honored ContributorI wonder why people are answering about FIR although the original post is asking for IIR. It should be also clear that a 2k taps FIR can't achieve the required fs/fc ratio, see previous thread http://www.alteraforum.com/forum/showthread.php?t=57301
80 dB stop band attenuation at 10*fc refers to a 4th order butterworth filter, two cascaded 2nd order blocks. As already mentioned in your previous thread, you need 27 extra fractional bits, refers to about 60 bit register width for 32 bit precision. A well considered design can process both 2nd order blocks sequentially using RAM based registers and coefficients. That's particularly interesting if you want to implement multiple filters. A test compile of a similar filter with parameters adjusted to your requirements uses 40 of 46 available DSP blocks of an EP4CE10, a few registers, about 1k LEs and some RAM. As also previously mentioned, the resource utilization can be reduced by switching to a modified implementation of the second order block, using two first order filters and an additional feedback.
