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-- All rights reserved. 

-- This file is part of VESTs (Vhdl tESTs).

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-- package under the terms of the "GNU GENERAL PUBLIC LICENSE" version 2,
-- June 1991. A copy of this license agreement can be found in the file
-- "COPYING", distributed with this archive.

-- 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 

-- ---------------------------------------------------------------------
--
-- $Id: clipper.ams,v 1.1 2002-03-27 22:11:19 paw Exp $
-- $Revision: 1.1 $
--
-- ---------------------------------------------------------------------

------------------------------------------------------------------------
-- Title         : Single diode clipper circuit
-- Project       : Mixed signal simulation
------------------------------------------------------------------------
-- File          : diode_clipper1.vhd
-- Author(s)     : Vasudevan Shanmugasundaram(vasu@ececs.uc.edu)
-- Created       : jan 16 1998
------------------------------------------------------------------------
-- Description : 
-- Behavioral description of a single diode clipper circuit.
------------------------------------------------------------------------
-- circuit diagram for the diode clipper:
--                                         the circuit comprises:
--  o______|l______o____|>|______o         i)  a diode D.
--  |      |l      |   diode D             ii) a constant voltage source vd.
--  |    const     |                       iii)a sinusoidal voltage source.
-- ( )    Vsource  >                       iv) a resistor R.
--  |Vs            >R
--  |              >
--  o______________|_____________o
--  
------------------------------------------------------------------------

--package definition
PACKAGE electricalSystem IS
NATURE electrical IS real ACROSS real THROUGH ground reference;
FUNCTION  SIN (X : real ) RETURN real;
FUNCTION EXP  (X : real ) RETURN real;
END PACKAGE electricalSystem;
-------------------------------------------------------------------------------

USE work.electricalSystem.all;

ENTITY diode_clipper IS
END diode_clipper;

ARCHITECTURE behav OF diode_clipper IS
    --terminal declarations
    terminal t1, t2, t3 : electrical;
    --quantity declarations
    quantity vDiode across iDiode through t1 TO t2;
    quantity v2 across i2 through t2 TO t3;
    quantity vd across electrical'reference TO t1;
    quantity vs across electrical'reference TO t3;
    --constants 
    CONSTANT saturation_current : real := 0.0000000000001;
    CONSTANT Vt : real := 0.025;        
    CONSTANT BV : real := 100.0;
    CONSTANT neg_sat : real := -saturation_current; 

BEGIN  -- behav
      if( vDiode >= (-1.0 * Vt)) USE --diode equations
        eqn1_1: iDiode == saturation_current * ( exp(vDiode/Vt) - 1.0 );
      ELSIF ((vDiode < (-3.0 * Vt)) AND (vDiode > -BV)) use
        eqn1_2:  iDiode == neg_sat;
      ELSE
        eqn1_3: iDiode == neg_sat * (exp(-(BV + vDiode)/Vt) - 1.0 +
				     saturation_current);
      END USE ;
      
      eqn2:     v2 == i2 * 100.0;  -- resistor eqn.

      eqn3:     vs == 20.0 * sin(2.0 * 3.1415 * 10000.0 * real(time'pos(now)) *
                   1.0e-15);  -- source

      eqn4:     vd == 5.0;  -- dc source
END behav;