Introducing mobility reduction over Vgs. Model parameter: theta

src/spicelib/devices/vdmos/vdmos.c

@@ -64,6 +64,7 @@ IFparm VDMOSmPTable[] = { /* model parameters */
  IOP("kp",    VDMOS_MOD_KP,    IF_REAL,   "Transconductance parameter"),
  IOP("phi",   VDMOS_MOD_PHI,   IF_REAL,   "Surface potential"),
  IOP("lambda",VDMOS_MOD_LAMBDA,IF_REAL,   "Channel length modulation"),
+ IOP("theta", VDMOS_MOD_THETA, IF_REAL,   "Vgs dependence on mobility"),
  IOP("rd",    VDMOS_MOD_RD,    IF_REAL,   "Drain ohmic resistance"),
  IOP("rs",    VDMOS_MOD_RS,    IF_REAL,   "Source ohmic resistance"),
  IOP("rg",    VDMOS_MOD_RG,    IF_REAL,   "Gate ohmic resistance"),

src/spicelib/devices/vdmos/vdmosdefs.h

@@ -265,8 +265,10 @@ typedef struct sVDMOSmodel {       /* model structure for a resistor */
     double VDMOSvt0; /* input - use tVto */
     double VDMOSphi; /* input - use tPhi */
     double VDMOSlambda;
+    double VDMOStheta;
     double VDMOSfNcoef;
     double VDMOSfNexp;
+
     double VDMOScgdmin;
     double VDMOScgdmax;
     double VDMOSa;
@@ -313,6 +315,7 @@ typedef struct sVDMOSmodel {       /* model structure for a resistor */
     unsigned VDIOdepletionCapCoeffGiven :1;
     unsigned VDMOSphiGiven   :1;
     unsigned VDMOSlambdaGiven    :1;
+    unsigned VDMOSthetaGiven    :1;
     unsigned VDMOStnomGiven  :1;
     unsigned VDMOSfNcoefGiven  :1;
     unsigned VDMOSfNexpGiven   :1;
@@ -367,6 +370,7 @@ enum {
     VDMOS_MOD_KP,
     VDMOS_MOD_PHI,
     VDMOS_MOD_LAMBDA,
+    VDMOS_MOD_THETA,
     VDMOS_MOD_RD,
     VDMOS_MOD_RS,
     VDMOS_MOD_RG,

src/spicelib/devices/vdmos/vdmosload.c

@@ -282,53 +282,58 @@ VDMOSload(GENmodel *inModel, CKTcircuit *ckt)
                  */
                 double betap;
                 double vgst;
+                double onfg, fgate, Betam, dfgdvg;
 
                 von = (model->VDMOSvt0*model->VDMOStype);
                 vgst = (here->VDMOSmode == 1 ? vgs : vgd) - von;
                 vdsat = MAX(vgst, 0);
+                onfg = 1.0+model->VDMOStheta*vgst;
+                fgate = 1.0/onfg;
+                Betam = Beta * fgate;
+                dfgdvg = -model->VDMOStheta*fgate*fgate;
                 /* drain current including subthreshold current
                  * numerical differentiation for gd and gm with a delta of 2 mV */
                 if (model->VDMOSksubthresGiven && (here->VDMOSmode == 1)) {
                     double delta = 0.001;
                     cdrain = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     /* gd */
                     double vds1 = vds + delta;
                     double cdrp = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     vds1 = vds - delta;
                     double cdrm = cweakinv(model->VDMOSksubthres, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, 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);
+                        Betam, 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);
+                        Betam, vt, model->VDMOSmtr);
+                    here->VDMOSgm = (cdrp - cdrm) / (2. * delta) * fgate + dfgdvg * cdrain;
                 }
                 else if (model->VDMOSsubslGiven && (here->VDMOSmode == 1)) {
                     double delta = 0.001;
                     cdrain = cweakinv2(model->VDMOSsubsl, model->VDMOSsubshift, vgst, vds, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     /* gd */
                     double vds1 = vds + delta;
                     double cdrp = cweakinv2(model->VDMOSsubsl, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     vds1 = vds - delta;
                     double cdrm = cweakinv2(model->VDMOSsubsl, model->VDMOSsubshift, vgst, vds1, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     here->VDMOSgds = (cdrp - cdrm) / (2. * delta);
                     /* gm */
                     double vgst1 = vgst + delta;
                     cdrp = cweakinv2(model->VDMOSsubsl, model->VDMOSsubshift, vgst1, vds, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
+                        Betam, vt, model->VDMOSmtr);
                     vgst1 = vgst - delta;
                     cdrm = cweakinv2(model->VDMOSsubsl, model->VDMOSsubshift, vgst1, vds, model->VDMOSlambda,
-                        Beta, vt, model->VDMOSmtr);
-                    here->VDMOSgm = (cdrp - cdrm) / (2. * delta);
+                        Betam, vt, model->VDMOSmtr);
+                    here->VDMOSgm = (cdrp - cdrm) / (2. * delta) * fgate + dfgdvg * cdrain;
                 } else {
                     if (vgst <= 0) {
                         /*
@@ -343,20 +348,20 @@ VDMOSload(GENmodel *inModel, CKTcircuit *ckt)
                          */
                         /* scale vds with mtr */
                         double mtr = model->VDMOSmtr;
-                        betap = Beta*(1 + model->VDMOSlambda*(vds*here->VDMOSmode));
+                        betap = Betam*(1 + model->VDMOSlambda*(vds*here->VDMOSmode));
                         if (vgst <= (vds * here->VDMOSmode) * mtr) {
                             cdrain = betap*vgst*vgst*.5;
-                            here->VDMOSgm = betap*vgst;
-                            here->VDMOSgds = model->VDMOSlambda*Beta*vgst*vgst*.5;
+                            here->VDMOSgm = betap*vgst * fgate + dfgdvg * cdrain;
+                            here->VDMOSgds = model->VDMOSlambda*Betam*vgst*vgst*.5;
                         } else {
                             /*
                              *     linear region
                              */
                             cdrain = betap * (vds * here->VDMOSmode) * mtr *
                                      (vgst - .5 * (vds*here->VDMOSmode) * mtr);
-                            here->VDMOSgm = betap * (vds * here->VDMOSmode) * mtr;
+                            here->VDMOSgm = betap * (vds * here->VDMOSmode) * mtr  * fgate + dfgdvg * cdrain;
                             here->VDMOSgds = betap * (vgst - (vds * here->VDMOSmode) * mtr) +
-                                             model->VDMOSlambda * Beta *
+                                             model->VDMOSlambda * Betam *
                                              (vds * here->VDMOSmode) * mtr *
                                              (vgst - .5 * (vds * here->VDMOSmode) * mtr);
                         }

src/spicelib/devices/vdmos/vdmosmask.c

@@ -36,6 +36,9 @@ VDMOSmAsk(CKTcircuit *ckt, GENmodel *inst, int which, IFvalue *value)
         case VDMOS_MOD_LAMBDA:
             value->rValue = model->VDMOSlambda;
             return(OK);
+        case VDMOS_MOD_THETA:
+            value->rValue = model->VDMOStheta;
+            return(OK);
         case VDMOS_MOD_RD:
             value->rValue = model->VDMOSdrainResistance;
             return(OK);

src/spicelib/devices/vdmos/vdmosmpar.c

@@ -35,6 +35,10 @@ VDMOSmParam(int param, IFvalue *value, GENmodel *inModel)
             model->VDMOSlambda = value->rValue;
             model->VDMOSlambdaGiven = TRUE;
             break;
+        case VDMOS_MOD_THETA:
+            model->VDMOStheta = value->rValue;
+            model->VDMOSthetaGiven = TRUE;
+            break;
         case VDMOS_MOD_RD:
             model->VDMOSdrainResistance = value->rValue;
             model->VDMOSdrainResistanceGiven = TRUE;

src/spicelib/devices/vdmos/vdmosset.c

@@ -54,6 +54,9 @@ VDMOSsetup(SMPmatrix *matrix, GENmodel *inModel, CKTcircuit *ckt,
         if (!model->VDMOSlambdaGiven) {
             model->VDMOSlambda = 0;
         }
+        if (!model->VDMOSthetaGiven) {
+            model->VDMOStheta = 0;
+        }
         if (!model->VDMOSfNcoefGiven) {
             model->VDMOSfNcoef = 0;
         }