JFET Noise Slope in LTSpice

[tec5c]

Hi all,

I have a SPICE model of a JFET (MPF102) which I found on the edaboard forums (model validity?), which I'll give here

.MODEL MPF102 NJF (VTO=-3.061588 BETA=286.155879m LAMBDA=20m IS=10f RS=239.291052 CGD=1.542479p CGS=2.567003p PB=1.49 KF=7.905907f AF=499.953m)

I am trying to understand what is defining the 1/f slope when the model is simulated for noise. AFAIK the flicker noise parameter 'EF' is what determines the slope, yet for whatever reason this parameter seems to be missing from the (/all) JFET model and I'm not sure why.

Here is the setup in LTSpice



Now, normally the EF parameter is default to 1. Which I believe translates to 1 decade of frequency should see the noise voltage vary by 1 decade. However, the data from LTSpice appears to be half of that, suggesting a squared factor is missing. Though with the given parameters in the JFET model, I can not figure out how I am able to change the slope.

Any help would be most appreciated.

[daddylonglegs]

  Page 125 of this manual:
http://ecee.colorado.edu/~mathys/ecen1400/pdf/scad3.pdf
  ... says that
KF is the Flicker noise coefficient
AF is the Flicker noise exponent
  ... and AF is set to AF=499.953m (i.e. 0.5) in your model. I would guess that the coefficient is the multiple that sets the noise baseline level and the exponent sets the variation with frequency but I don't know for sure.