On Wed, 19 Feb 2014 11:05:48 -0600, amdx wrote:
Not by much. FETs come with capacitance included. You might find a better one, but it'll only be a factor of two, max.
Here comes the Spice:
Version 4 SHEET 1 880 680 WIRE 208 -80 48 -80 WIRE 48 -64 48 -80 WIRE 48 32 48 16 WIRE 208 96 208 -80 WIRE -80 160 -144 160 WIRE 112 160 -16 160 WIRE 160 160 112 160 WIRE 112 208 112 160 WIRE 208 224 208 192 WIRE 336 224 208 224 WIRE -144 240 -144 160 WIRE 208 240 208 224 WIRE 112 336 112 288 WIRE -144 448 -144 320 WIRE 112 448 112 416 WIRE 112 448 -144 448 WIRE 208 448 208 320 WIRE 208 448 112 448 WIRE 112 512 112 448 FLAG 48 32 0 FLAG 112 512 0 FLAG 336 224 out IOPIN 336 224 Out FLAG -144 160 in IOPIN -144 160 In SYMBOL njf 160 96 R0 SYMATTR InstName J1 SYMATTR Value BF256C SYMBOL res 192 224 R0 SYMATTR InstName R1 SYMATTR Value 470 SYMBOL res 96 192 R0 SYMATTR InstName R2 SYMATTR Value 10meg SYMBOL cap -16 144 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 0.3p SYMBOL voltage 48 -80 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 96 320 R0 SYMATTR InstName R3 SYMATTR Value 10meg SYMBOL voltage -144 224 R0 WINDOW 123 24 106 Left 2 WINDOW 39 24 116 Left 2 SYMATTR Value2 AC 1 SYMATTR SpiceLine Rser=0 SYMATTR InstName V2 SYMATTR Value "" TEXT -312 232 Left 2 !.ac dec 1000 1k 10meg TEXT -312 264 Left 2 !.net I(R1) v2 TEXT -424 72 Left 2 !.model BF256C NJF(Beta=1.4m Betatce=-.5 Rd=1 Rs=1 Lambda=4.6m Vto=-3.1\n+ Vtotc=-2.5m Is=33.57f Isr=322.4f N=1 Nr=2 Xti=3 Alpha=311.7u\n+ Vk=243.6 Cgd=2.132p M=.3622 Pb=1 Fc=.5 Cgs=2.104p Kf=23.06E-18\n+ Af=1)
And the plot file:
[AC Analysis] { Npanes: 2 Active Pane: 1 { traces: 1 {8388611,0,"Zout(v2)"} X: ('M',0,1000,0,1e+007) Y[0]: (' ',0,210,30,540) Y[1]: (' ',0,-40,20,180) Log: 1 0 0 GridStyle: 1 PltReal: 1 PltImag: 1 Representation: 2 }, { traces: 1 {8388610,0,"Zin(v2)"} X: ('M',0,1000,0,1e+007) Y[0]: ('M',0,0,2e+006,2.2e+007) Y[1]: ('M',0,-5.5e+008,5e+007,0) Log: 1 0 0 GridStyle: 1 PltReal: 1 PltImag: 1 Representation: 2 } }