Hey, Phil,
Your SAV-551 Spice model is
.MODEL SAV551 NMF(vto=0.08, Beta=0.3,
- Lambda=0.07, Alpha=4 B=0.8, Pb=0.7,
- Cgs=0.997E-12, Cgd=0.176E-12, Rd=0.084,
- Rs=0.054, Kf=5e-11, Af=2)
I was looking at the SAV-541. It conducts harder than 551 but looks about the same otherwise. I measured gate and drain capacitances and they look about the same. The s-params suggest a bit more capacitance for the 541 but they are at different currents.
Rds-on is about the same, about 2.5 ohms, but the data sheet drain curve of the 541 is a lot beefier. (Who measures Rds-on of a phemt?)
With the same capacitances but more drain current capability, it should switch faster.
What might I change in your model for a SAV-541? I could simulate and see how it aligns with the data sheet.
I wonder why the 551 is rated for 0.45 to 6 GHz and the 541 is rated for 0.045 to 6 GHz. That's weird.