#658 Documentation says JFET2 supports AFAC parameter but it is not in source code

[simpletk]

I need to simulate "forward gate bias" of JFET transistor. In the documentation (https://ngspice.sourceforge.io/docs/ngspice-manual.pdf) on page 154 it says that JFET model 2 is capable of:

Extreme operating regions - subthreshold, forward gate bias, controlled resistance,
and breakdown regions - are included.

So I tried to use JFET model 2. The current through gate-source diode iGS uses parameter AFAC as described in this PDF (https://ngspice.sourceforge.io/external-documents/models/psfet.pdf) which is also linked in the ngspicejs pdf on the page 154.

* first line is ignored
.model QJ201_V2 NJF(level=2 acgam=0 beta=0.0001 cgd=0 cgs=0 
+delta=0 fc=0.5 hfeta=0 hfe1=0 hfe2=0 hfgam=0 hfg1=0 hfg2=0
+ibd=0 is=1e-14 lfgam=0 lfg1=0 lfg2=0 mvst=0 n=1 p=2 q=2 
+rs=0 rd=0 taud=0 taug=0 vbd=1 vbi=1 vst=0 vto=-2 xc=0 xi=1000
+z=1 rg=0 lg=0 ls=0 ld=0 cdss=0 afac=1 nfing=1 tnom=300 temp=300)
V_U1 5 0 DC 9
V_A1 5 4 DC 0
R_R1 4 3 220
J_J1 3 g 0 QJ201_V2
V_U2 g 0 DC 0
.print tran all
.tran 20u 20m 0
.end

However ngspice reports that AFAC is unrecognized parameter (rg, lg, ls, ld, cdss, afac, nfing are not recognized).

I checked ngspice-42 sources and there is no such parameter in jfet 2 code.

[Dietmar Warning]

I see no bug here - extended geometry scaling is simple not implemented.
The referenced document has neither author nor reference to the actual implementation.
Our manual makes no distinction what is implemented and what not and should revised in that point.