include/u_limit.h

   1 /* $Id: u_limit.h,v 26.81 2008/05/27 05:34:00 al Exp $ -*- C++ -*-
   2  * Copyright (C) 2006 Albert Davis
   3  * Author: Albert Davis <aldavis@gnu.org>
   4  *
   5  * This file is part of "Gnucap", the Gnu Circuit Analysis Package
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 3, or (at your option)
  10  * any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  20  * 02110-1301, USA.
  21  *------------------------------------------------------------------
  22  * device limiting library
  23  */
  24 //testing=script 2006.07.14
  25 #ifndef U_LIMIT_H
  26 #define U_LIMIT_H
  27 #include "md.h"
  28 /*--------------------------------------------------------------------------*/
  29 /* Spice style PN junction limiting */
  30 inline double pnj_limit(double vnew, double vold, double vt, double vcrit)
  31 {
  32   trace4("limit-in", vnew, vold, vt, vcrit);
  33   if ((vnew > vcrit) && (std::abs(vnew - vold) > (2 * vt))) {
  34     if (vold > 0) {
  35       double arg = 1 + (vnew - vold) / vt;
  36       double vlim = (arg > 0) ? (vold + vt * log(arg)) : vcrit;
  37       trace3("limit-1", vlim, vt*log(arg), arg);
  38       return vlim;
  39     }else{
  40       double vlim = vt * log(vnew/vt);
  41       trace3("limit-2", vlim, vt*log(vnew/vt), vnew/vt);
  42       return vlim;
  43     }
  44   }else{
  45     trace1("limit-3", vnew);
  46     return vnew;
  47   }
  48 }
  49 /*--------------------------------------------------------------------------*/
  50 inline double fet_limit_vds(double vnew, double vold)
  51 {
  52   if (vold >= 3.5) {
  53     if (vnew > (3*vold + 2)) {itested();
  54       return 3 * vold + 2;
  55     }else if (vnew < 2) {
  56       return 2;
  57     }else{
  58       return vnew;
  59     }
  60   }else{
  61     if (vnew > 4) {
  62       return 4;
  63     }else if (vnew < -.5) {
  64       return -.5;
  65     }else{
  66       return vnew;
  67     }
  68   }
  69 }
  70 /*--------------------------------------------------------------------------*/
  71 inline double fet_limit_vgs(double vnew, double vold, double vto)
  72 {
  73   assert(vnew == vnew);
  74   assert(vold == vold);
  75
  76   double vgst_old = vold - vto;
  77   double vgst_new = vnew - vto;
  78   double v_limited;
  79   if (vgst_old >= 3.5) { /* was strong on */
  80     if (vgst_new < 2) {
  81       v_limited = 2;
  82     }else if (vgst_new > (3 * vgst_old + 2)) {itested();
  83       v_limited = 3*vgst_old + 2;
  84     }else{
  85       v_limited = vgst_new;
  86     }
  87   }else if (vgst_old >= 0) { /* middle region, on */
  88     assert(vgst_old < 3.5);
  89     if (vgst_new < -.5) {
  90       v_limited = -.5;
  91     }else if (vgst_new > 4) {
  92       v_limited = 4;
  93     }else{
  94       v_limited = vgst_new;
  95     }
  96   }else if (vgst_old <= 0) { /* was off, vgst_old < 0 */
  97     assert(vgst_old < 0);
  98     if (vgst_new < (3 * vgst_old - 2)) {
  99       v_limited = 3*vgst_old - 2;
 100     }else if (vgst_new > .5) {
 101       v_limited = .5;
 102     }else{
 103       v_limited = vgst_new;
 104     }
 105   }else{ /* overflow or other numeric error */
 106     // not sure what to do in this case.
 107     // It could actually happen with overflow or divide by zero.
 108     // but supposedly this is trapped elsewhere.
 109     unreachable();
 110     v_limited = 0.;
 111     trace3("huh?", vnew, vold, vto);
 112     trace3("    ", vgst_new, vgst_old, v_limited);
 113   }
 114   return v_limited + vto;
 115 }
 116 /*--------------------------------------------------------------------------*/
 117 /*--------------------------------------------------------------------------*/
 118 #endif
 119 // vim:ts=8:sw=2:noet: