introduce parameter ksubthres, compatible to LTSPICE

src/spicelib/devices/vdmos/vdmos.c

@@ -87,6 +87,7 @@ IFparm VDMOSmPTable[] = { /* model parameters */
  /* weak inversion */
  IOP("subslope",  VDMOS_MOD_SUBSLOPE,   IF_REAL, "Slope of weak inversion log current versus vgs - vth"),
  IOP("subshift",  VDMOS_MOD_SUBSHIFT,   IF_REAL, "Shift of weak inversion plot on the vgs axis"),
+ IOP("ksubthres", VDMOS_MOD_KSUBTHRES,  IF_REAL, "Shift of weak inversion plot on the vgs axis"),
 
 /* body diode */
  IOP("bv",    VDMOS_MOD_BV,    IF_REAL,   "Vds breakdown voltage"),

src/spicelib/devices/vdmos/vdmosdefs.h

@@ -334,6 +334,7 @@ typedef struct sVDMOSmodel {       /* model structure for a resistor */
     double VDMOScgs;
     double VDMOSsubsl;
     double VDMOSsubshift;
+    double VDMOSksubthres;
     double VDMOSmtr;
 
     /* bulk diode */
@@ -383,6 +384,7 @@ typedef struct sVDMOSmodel {       /* model structure for a resistor */
     unsigned VDMOSaGiven   :1;
     unsigned VDMOSsubslGiven   :1;
     unsigned VDMOSsubshiftGiven   :1;
+    unsigned VDMOSksubthresGiven :1;
     unsigned VDMOSmtrGiven   :1;
 
     unsigned VDMOSDbvGiven   :1;
@@ -452,6 +454,7 @@ enum {
     VDMOS_MOD_MTRIODE,
     VDMOS_MOD_SUBSLOPE,
     VDMOS_MOD_SUBSHIFT,
+    VDMOS_MOD_KSUBTHRES,
     VDMOS_MOD_BV,
     VDMOS_MOD_IBV,
     VDMOS_MOD_NBV,

src/spicelib/devices/vdmos/vdmosload.c

@@ -367,7 +367,29 @@ VDMOSload(GENmodel *inModel, CKTcircuit *ckt)
                 arg = 0;
                 /* drain current including subthreshold current
                  * numerical differentiation for gd and gm with a delta of 2 mV */
-                if (model->VDMOSsubslGiven && (here->VDMOSmode == 1)) {
+                if (model->VDMOSksubthresGiven && (here->VDMOSmode == 1)) {
+                    double delta = 0.001;
+                    cdrain = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds, model->VDMOSlambda,
+                        Beta, vt, model->VDMOSmtr);
+                    /* gd */
+                    double vds1 = vds + delta;
+                    double cdrp = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
+                        Beta, vt, model->VDMOSmtr);
+                    vds1 = vds - delta;
+                    double cdrm = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
+                        Beta, vt, model->VDMOSmtr);
+                    here->VDMOSgds = (cdrp - cdrm) / (2. * delta);
+                    /* gm */
+                    double vgst1 = vgst + delta;
+                    cdrp = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst1, vds, model->VDMOSlambda,
+                        Beta, vt, model->VDMOSmtr);
+                    vgst1 = vgst - delta;
+                    cdrm = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst1, vds, model->VDMOSlambda,
+                        Beta, vt, model->VDMOSmtr);
+                    here->VDMOSgm = (cdrp - cdrm) / (2. * delta);
+                    here->VDMOSgmbs = 0.;
+                }
+                else if (model->VDMOSsubslGiven && (here->VDMOSmode == 1)) {
                     double delta = 0.001;
                     cdrain = cweakinv(model->VDMOSsubsl, model->VDMOSsubshift, vgst, vds, model->VDMOSlambda,
                         Beta, vt, model->VDMOSmtr);

src/spicelib/devices/vdmos/vdmosmask.c

@@ -60,6 +60,9 @@ VDMOSmAsk(CKTcircuit *ckt, GENmodel *inst, int which, IFvalue *value)
         case VDMOS_MOD_SUBSHIFT:
             value->rValue = model->VDMOSsubshift;
             return(OK);
+        case VDMOS_MOD_KSUBTHRES:
+            value->rValue = model->VDMOSksubthres;
+            return(OK);
         case VDMOS_MOD_TYPE:
             if (model->VDMOStype > 0)
                 value->sValue = "vdmosn";

src/spicelib/devices/vdmos/vdmosmpar.c

@@ -141,6 +141,10 @@ VDMOSmParam(int param, IFvalue *value, GENmodel *inModel)
             model->VDMOSsubshift = value->rValue;
             model->VDMOSsubshiftGiven = TRUE;
             break;
+        case VDMOS_MOD_KSUBTHRES:
+            model->VDMOSksubthres = value->rValue;
+            model->VDMOSksubthresGiven = TRUE;
+            break;
         case VDMOS_MOD_BV:
             model->VDMOSDbv = value->rValue;
             model->VDMOSDbvGiven = TRUE;

src/spicelib/devices/vdmos/vdmosset.c

@@ -78,6 +78,9 @@ VDMOSsetup(SMPmatrix *matrix, GENmodel *inModel, CKTcircuit *ckt,
         if (!model->VDMOSsubshiftGiven) {
             model->VDMOSsubshift = 0;
         }
+        if (!model->VDMOSksubthresGiven) {
+            model->VDMOSksubthres = 0;
+        }
         if (!model->VDMOSmtrGiven) {
             model->VDMOSmtr = 1.;
         }