-------------------------------------------------------------------------------
-- Copyright (c) 2001 Mentor Graphics Corporation
--
-- This model is a component of the Mentor Graphics VHDL-AMS educational open 
-- source model library, and is covered by this license agreement. This model,
-- including any updates, modifications, revisions, copies, and documentation 
-- are copyrighted works of Mentor Graphics. USE OF THIS MODEL INDICATES YOUR 
-- COMPLETE AND UNCONDITIONAL ACCEPTANCE OF THE TERMS AND CONDITIONS SET FORTH
-- IN THIS LICENSE AGREEMENT.  Mentor Graphics grants you a non-exclusive 
-- license to use, reproduce, modify and distribute this model, provided that:
-- (a) no fee or other consideration is charged for any distribution except 
-- compilations distributed in accordance with Section (d) of this license 
-- agreement; (b) the comment text embedded in this model is included verbatim
-- in each copy of this model made or distributed by you, whether or not such 
-- version is modified; (c) any modified version must include a conspicuous 
-- notice that this model has been modified and the date of modification; and 
-- (d) any compilations sold by you that include this model must include a 
-- conspicuous notice that this model is available from Mentor Graphics in its
-- original form at no charge.
--
-- THIS MODEL IS LICENSED TO YOU "AS IS" AND WITH NO WARRANTIES, EXPRESS OR 
-- IMPLIED.  MENTOR GRAPHICS SPECIFICALLY DISCLAIMS ALL IMPLIED WARRANTIES OF 
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-- HAVE NO RESPONSIBILITY FOR ANY DAMAGES WHATSOEVER.
-------------------------------------------------------------------------------
-- File       : diode.vhd
-- Author     : Mentor Graphics
-- Created    : 2001/06/16
-- Last update: 2003-05-13
-------------------------------------------------------------------------------
-- Description: Basic Diode model 
-------------------------------------------------------------------------------
-- Revisions  :
-- Date        Version     Author              Description
-- 2001/06/16  1.0         Mentor Graphics     Created
-- 2001/11/07  1.1         Mentor Graphics     Added limit_exp function
-- 2001/05/24  1.2         Mentor Graphics     Added Generic parameter Isat
-------------------------------------------------------------------------------

library IEEE;
use IEEE.math_real.all;
-- Use IEEE natures and packages
use IEEE.electrical_systems.all;
-- FUNDAMENTAL_CONSTANTS package needed for Boltzmann constant
-- (PHYS_K = Joules/Kelvin) and electron charge (PHYS_Q = coulomb)
use IEEE.FUNDAMENTAL_CONSTANTS.all;

entity diode is
  generic (
    Isat   : current := 1.0e-14);   -- Saturation current [Amps]
  port (
    terminal p, n : electrical);

end entity diode;

-------------------------------------------------------------------------------
-- Ideal Architecture: i = is*(exp(v/vt) - 1)
-------------------------------------------------------------------------------
architecture ideal of diode is
  
-- Declare internal quanties and constants
  quantity v across i through p to n;
  constant TempC : real    := 27.0;           		-- Ambient Temperature [Degrees]
  constant TempK : real    := 273.0 + TempC;  		-- Temperaure [Kelvin] 
  constant vt    : real    := PHYS_K*TempK/PHYS_Q;    -- Thermal Voltage

  -- This function is to limit the exponential function to avoid convergence
  -- problems due to numerical overflow. At x=100, it becomes a straight line
  -- with slope matching that at the intercept.  
  function limit_exp( x : real ) return real is
    variable abs_x      : real := abs(x);
    variable result     : real;
  begin
    if abs_x < 100.0 then
      result := exp(abs_x);
    else
      result := exp(100.0) * (abs_x - 99.0);
    end if;
  -- If exponent is negative, set exp(-x) = 1/exp(x)  
    if x < 0.0 then
      result := 1.0 / result;
    end if;
    return result;
  end function limit_exp;
begin  -- ideal architecture

-- Fundamental equation
  i == Isat*(limit_exp(v/vt) - 1.0);

end architecture ideal;

-------------------------------------------------------------------------------
-- Copyright (c) 2001 Mentor Graphics Corporation
-------------------------------------------------------------------------------