-------------------------------------------------------------------------------
-- Second Order Lowpass filter
--
--  Transfer Function:
--
--                    w1*w2         
--   H(s) =  k * ----------------
--               (s + w1)(s + w2)
--
-- DC Gain = k
-------------------------------------------------------------------------------

-- Use IEEE_proposed instead of disciplines
library IEEE;
use IEEE.electrical_systems.all;
library IEEE;
use ieee.math_real.all;

entity lpf_1_e is
  generic (
    fp   : real;            -- pole freq
    gain : real := 1.0);    -- filter gain

    port 	(	terminal input: electrical;
			terminal output: electrical);
end entity lpf_1_e;

architecture simple of lpf_1_e is
  QUANTITY vin ACROSS input TO ELECTRICAL_REF;
  QUANTITY vout ACROSS iout THROUGH output TO ELECTRICAL_REF;

  constant wp : real := math_2_pi*fp;    
  constant num : real_vector := (0 => wp*gain);  -- 0=> is needed to give
                                                   -- index when only a single
                                                   -- element is used.
  constant den : real_vector := (wp, 1.0);
  quantity vin_temp : real;  

begin
	vin_temp == vin;   -- intermediate variable (vin) req'd for now
	vout == vin_temp'ltf(num, den);
end architecture simple;