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-- Copyright (C) 2002 Morgan Kaufmann Publishers, Inc
-- This file is part of VESTs (Vhdl tESTs).
-- VESTs is free software; you can redistribute it and/or modify it
-- under the terms of the GNU General Public License as published by the
-- Free Software Foundation; either version 2 of the License, or (at
-- your option) any later version.
-- VESTs is distributed in the hope that it will be useful, but WITHOUT
-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-- FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
-- for more details.
-- You should have received a copy of the GNU General Public License
-- along with VESTs; if not, write to the Free Software Foundation,
-- Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
library ieee; use ieee.math_real.all;
library ieee_proposed; use ieee_proposed.electrical_systems.all;
entity lowpass is
generic ( fp : real := 10.0; -- pole in Hz for 'zoh, 'delayed
Fsmp : real := 10.0e3 ); -- sample frequency for 'zoh, 'delayed
port ( terminal input : electrical;
terminal output: electrical );
end entity lowpass;
----------------------------------------------------------------
architecture z_minus_1 of lowpass is
quantity vin across input to electrical_ref;
quantity vout across iout through output to electrical_ref;
quantity vin_sampled : real; -- discrete sample of input quantity
quantity vin_zm1, vout_zm1 : real; -- z**-1
constant Tsmp : real := 1.0 / Fsmp; -- sample period
constant wp : real := fp * math_2_pi; -- pole in rad/s
constant n0 : real := Tsmp * wp; -- z0 numerator coefficient
constant n1 : real := Tsmp * wp; -- z-1 numerator coefficient
constant d0 : real := Tsmp * wp + 2.0; -- z0 denominator coefficient
constant d1 : real := Tsmp * wp - 2.0; -- z-1 denominator coefficient
begin
vin_sampled == vin'zoh(Tsmp);
vin_zm1 == vin_sampled'delayed(Tsmp);
vout_zm1 == vout'delayed(Tsmp);
vout == vin_sampled * n0 / d0 + n1 * vin_zm1 / d0 - d1 * vout_zm1 / d0;
end z_minus_1;
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