myopenid,
I reviewed the circuits and there is a slight, but very important difference...
If you look carefully at the '2N5484' model, in "Non-Working" Circuit... (you'll see parameters CGS, CGD) - these are valid Capacitance Gate-Source, Capacitance Gate-Drain values...
J1 10 20 30 NJF
.MODEL NJF NJF
+ VTO = -1.2796E+000
+ BETA = 1.71347E-003
+ LAMBDA = 1.93292E-002
+ RD = 4.41873E+000
+ RS = 4.41873E+000
+ IS = 1.25479E-016
+ CGS = 2.25000E-012
+ CGD = 2.34000E-012
+ PB = 1.14141E+000
+ FC = 5.00000E-001
In the '2N5484' model of the "Working" Circuit... (you'll see CGS0, CGD0)
J1 10 20 30 NJF
.MODEL NJF NJF
+ VTO = -1.2796E+000
+ BETA = 1.71347E-003
+ LAMBDA = 1.93292E-002
+ RD = 4.41873E+000
+ RS = 4.41873E+000
+ IS = 1.25479E-016
+ CGSO = 2.25000E-012
+ CGDO = 2.34000E-012
+ PB = 1.14141E+000
+ FC = 5.00000E-001
However if you look at the Simulation tab, you'll find that parameters CGS0, CGD0 are invalid and not supported (which makes them 0 in the model, i.e. no capacitance).
Basically looking at your operating frequency, you have a 1Ghz source, and with no G-S or G-D capacitance you can run the 'working' circuit at this frequency (no device capacitance), which is likely not realistic, but with the actual values for the '2N5484' in place of 2.25pF and 2.34pF respectively, basically the cascode amplifier will not work at this frequency...
- Regards,
Pat Noonan
National Instruments
