jfet: new noise model selector nlev=3 for correct noise in non-saturated region

src/spicelib/devices/jfet/jfet.c

@@ -70,7 +70,9 @@ IFparm JFETmPTable[] = { /* model parameters */
  IOP("kf",  JFET_MOD_KF, IF_REAL, "Flicker Noise Coefficient"),
  IOP("af",  JFET_MOD_AF, IF_REAL, "Flicker Noise Exponent"),
  IOP("tcv", JFET_MOD_TCV, IF_REAL, "Threshold voltage temperature coefficient"),
- IOP("bex", JFET_MOD_BEX, IF_REAL, "Mobility temperature exponent")
+ IOP("bex", JFET_MOD_BEX, IF_REAL, "Mobility temperature exponent"),
+ IOP("nlev",JFET_MOD_NLEV, IF_INTEGER, "Noise equation selector"),
+ IOP("gdsnoi", JFET_MOD_GDSNOI, IF_REAL, "Channel noise coefficient")
 };
 
 

src/spicelib/devices/jfet/jfetdefs.h

@@ -188,7 +188,8 @@ typedef struct sJFETmodel {       /* model structure for a jfet */
     double JFETdepletionCapCoeff;
     double JFETfNcoef;
     double JFETfNexp;
-
+    int JFETnlev;
+    double JFETgdsnoi;
 
     double JFETdrainConduct;
     double JFETsourceConduct;
@@ -218,6 +219,8 @@ typedef struct sJFETmodel {       /* model structure for a jfet */
     unsigned JFETtnomGiven : 1; /* user specified Tnom for model */
     unsigned JFETfNcoefGiven : 1;
     unsigned JFETfNexpGiven : 1;
+    unsigned JFETnlevGiven : 1;
+    unsigned JFETgdsnoiGiven : 1;
     unsigned JFETtcvGiven : 1;
     unsigned JFETbexGiven : 1;
 
@@ -261,6 +264,8 @@ typedef struct sJFETmodel {       /* model structure for a jfet */
 /* end Sydney University mod */
 #define JFET_MOD_TCV 117
 #define JFET_MOD_BEX 118
+#define JFET_MOD_NLEV 119
+#define JFET_MOD_GDSNOI 120
 
 /* device questions */
 #define JFET_DRAINNODE        301

src/spicelib/devices/jfet/jfetmask.c

@@ -89,6 +89,12 @@ JFETmAsk(CKTcircuit *ckt, GENmodel *inModel, int which, IFvalue *value)
             else
                 value->sValue = "pjf";
             return(OK);
+        case JFET_MOD_NLEV:
+            value->iValue = model->JFETnlev;
+            return(OK);
+        case JFET_MOD_GDSNOI:
+            value->rValue = model->JFETgdsnoi;
+            return(OK);
         default:
             return(E_BADPARM);
     }

src/spicelib/devices/jfet/jfetmpar.c

@@ -94,6 +94,14 @@ JFETmParam(int param, IFvalue *value, GENmodel *inModels)
             model->JFETbexGiven = TRUE;
             model->JFETbex = value->rValue;
             break;
+        case JFET_MOD_NLEV:
+            model->JFETnlevGiven = TRUE;
+            model->JFETnlev = value->iValue;
+            break;
+        case JFET_MOD_GDSNOI:
+            model->JFETgdsnoiGiven = TRUE;
+            model->JFETgdsnoi = value->rValue;
+            break;
         default:
             return(E_BADPARM);
     }

src/spicelib/devices/jfet/jfetnoi.c

@@ -35,6 +35,7 @@ JFETnoise (int mode, int operation, GENmodel *genmodel, CKTcircuit *ckt, Ndata *
     double noizDens[JFETNSRCS];
     double lnNdens[JFETNSRCS];
     int i;
+    double vgs, vds, vgst, alpha, beta;
 
     /* define the names of the noise sources */
 
@@ -112,10 +113,26 @@ JFETnoise (int mode, int operation, GENmodel *genmodel, CKTcircuit *ckt, Ndata *
                                  inst->JFETsourceNode,model->JFETsourceConduct 
                                  * inst->JFETarea * inst->JFETm);
 
-                    NevalSrc(&noizDens[JFETIDNOIZ],&lnNdens[JFETIDNOIZ],
-                                 ckt,THERMNOISE,inst->JFETdrainPrimeNode,
-                                 inst->JFETsourcePrimeNode,
-                                 (2.0/3.0 * inst->JFETm * fabs(*(ckt->CKTstate0 + inst->JFETgm))));
+                    if (model->JFETnlev < 3) {
+                        NevalSrc(&noizDens[JFETIDNOIZ],&lnNdens[JFETIDNOIZ],
+                                     ckt,THERMNOISE,inst->JFETdrainPrimeNode,
+                                     inst->JFETsourcePrimeNode,
+                                     (2.0/3.0 * inst->JFETm * fabs(*(ckt->CKTstate0 + inst->JFETgm))));
+                    } else {
+                        vgs = *(ckt->CKTstate0 + inst->JFETvgs);
+                        vds = vgs - *(ckt->CKTstate0 + inst->JFETvgd);
+                        vgst = vgs - inst->JFETtThreshold;
+                        if (vgst >= vds)
+                            alpha = 1 - vds/vgst; /* linear region */
+                        else
+                            alpha = 0;        /* saturation region */
+                        beta = inst->JFETtBeta * inst->JFETarea * inst->JFETm;
+
+                        NevalSrc(&noizDens[JFETIDNOIZ],&lnNdens[JFETIDNOIZ],
+                                     ckt,THERMNOISE,inst->JFETdrainPrimeNode,
+                                     inst->JFETsourcePrimeNode,
+                                     (2.0/3.0 * beta*vgst*(1+alpha+alpha*alpha)/(1+alpha)*model->JFETgdsnoi));
+                    }
 
                     NevalSrc(&noizDens[JFETFLNOIZ], NULL, ckt,
                                  N_GAIN,inst->JFETdrainPrimeNode,

src/spicelib/devices/jfet/jfetset.c

@@ -81,6 +81,12 @@ JFETsetup(SMPmatrix *matrix, GENmodel *inModel, CKTcircuit *ckt, int *states)
         if(!model->JFETbexGiven) {
             model->JFETbex = 0.0;
         }
+        if(!model->JFETnlevGiven) {
+            model->JFETnlev = 2;
+        }
+        if(!model->JFETgdsnoiGiven) {
+            model->JFETgdsnoi = 1.0;
+        }
 
         if(model->JFETdrainResist != 0) {
             model->JFETdrainConduct = 1/model->JFETdrainResist;