-- ------------------------------------------------------------- -- Additional material to the book-- Modeling and Simulation for RF System Design-- ---- THIS MODEL IS LICENSED TO YOU "AS IT IS" AND WITH NO WARRANTIES, -- EXPRESSED OR IMPLIED. THE AUTHORS SPECIFICALLY DISCLAIM ALL IMPLIED -- WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.-- THEY MUST NOT HAVE ANY RESPONSIBILITY FOR ANY DAMAGES, FINANCIAL OR-- LEGAL CLAIMS WHATEVER.-- ------------------------------------------------------------- Name:     Lowpass filter-- -- Description:-- This part describes the filter package with functions for-- computation of lowpass filter coefficients---- Literature:-- ---- Dependencies: -- ------------------------------------------------------------- Logical Library         Design unit-- ------------------------------------------------------------- IEEE                    MATH_REAL-- --------------------------------------------------------------- Source:-- filter_functions_header.vhd-- -----------------------------------------------------------library IEEE;  use IEEE.MATH_REAL.all;package FILTER is  -- -------------------------------------------------------------------------  -- Coefficients for normalized lowpass filter  --   -- LP(s) = 1.0 / (1 + a*S + b*S^2)  -- -------------------------------------------------------------------------  function LOWPASS_BUTTERWORTH_A            (GRAD : INTEGER)    -- grade of filter  return REAL_VECTOR;          -- array with filter coefficients   function LOWPASS_BUTTERWORTH_B            (GRAD : INTEGER)    -- grade of filter  return REAL_VECTOR;          -- array with filter coefficientsend package FILTER;