Low Pass IIR filter using cyclone II FPGA

Ok guys,

I did just like you told me: maximum of my ai, bi, i=1,...,7 coeff is -20.023...

I did the simulations and 18 [6.12] coefficients bit resolution fits my output mask. So I overcome the problem with coeff representation and I represent the coeff in a two's complement representation with 18bits (6.12).

I'm trying to understand how to perform multiplication of sampled digitalized signal x(n-i) and coefficient ai, bi. How to perform the multiplication when I have coefficient ai, bi in a two's complement representation with a fixed point and digitalized semple (output of A/D converter) x(n-i) which is not in a two's complement and don't have fractional part.

If you understand my problem and have any idea please advice me.

Thank you very very much!

Bojan