Phil,

I don't have any E-pHEMT models, and LTspice doesn't understand the Avago datasheet models.

I've used this one in the past:

• Depletion pHEMT

• This is the datasheet model, except that LTspice doesn't understand a bunch of

• the parameters given by Avago--we'll see if it works

.MODEL ATF38143_chip NMF( vto=-0.75, 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=1e6, Af=1)

There are also these:

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Cool. Thanks. It works as a depletion mesfet. I can tweak that to make it work more like a SAV541. Might add some drain inductance maybe. I will use the 541 as a switch to discharge the cap in a linear ramp generator, so the model can be a little crude; it's not likely to oscillate!

Version 4 SHEET 1 880 680 WIRE 288 -96 64 -96 WIRE 64 -32 64 -96 WIRE 64 96 64 48 WIRE 128 96 64 96 WIRE 176 96 128 96 WIRE 64 160 64 96 WIRE 288 160 288 -96 WIRE -64 240 -128 240 WIRE 16 240 -64 240 WIRE -128 272 -128 240 WIRE 64 304 64 256 WIRE 288 304 288 240 WIRE -128 384 -128 352 FLAG 64 304 0 FLAG 288 304 0 FLAG -128 384 0 FLAG -64 240 G FLAG 128 96 D SYMBOL mesfet 16 160 R0 WINDOW 0 100 31 Left 2 WINDOW 3 89 65 Left 2 SYMATTR InstName Z1 SYMATTR Value SAV SYMBOL voltage 288 144 R0 WINDOW 0 55 47 Left 2 WINDOW 3 63 77 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL res 48 -48 R0 WINDOW 0 -72 45 Left 2 WINDOW 3 -74 84 Left 2 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL voltage -128 256 M0 WINDOW 0 62 58 Left 2 WINDOW 3 51 96 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value SINE(-0.5 1 1) TEXT -160 464 Left 2 !.MODEL SAV NMF( vto=-0.75, Beta=0.3, Lambda=0.07, Alpha=4,\n+ B=0.8, Pb=0.7, Cgs=0.997E-12,\n+ Cgd=0.176E-12, Rd=0.084, Rs=0.054, Kf=1e6, Af=1) TEXT 128 392 Left 2 !.tran 5 TEXT 376 320 Left 2 ;First cut at SAV541 model TEXT 376 360 Left 2 ;using Phil's mesfet model TEXT 432 408 Left 2 ;JL Jan 5 2020

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The other link I posted has the package parasitics, which are probably pretty similar.

Just for fun I instrumented your circuit and found that VAF is right around 14 volts for this model. I think that might be a bit optimistic for the Avago part.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

On 06.01.20 1:03 am, snipped-for-privacy@highlandsniptechnology.com wrote: > Do you have a Spice model for SAV551 or something similar?

I don't, at least not for LTspice, but would be interested in one. The obvious choice would be to use the ATF-55134 model from the Agilent/Avago datasheet and hope it's close enough:

(page 16)

Unfortunately, that happens to use the ADS-flavoured quadratic Curtice model, though, which other SPICEs don't implement. You could try and use this as a basis for further fiddling:

.MODEL SAV551 NMF(Vto=0.3, Beta=0.444, B=0.8, Alpha=13, Lambda=0.072, Rd=2.025, Rs=0.675, Cgs=0.6193E-12, Cgd=0.1435E-12, Pb=0.7, Fc=0.65)

This is a mechanical translation of the coefficients from the datasheet, which might or might not give sensible results. You'd need to tune the B value to match your measurements? Package parasitics could be included in a SUBCKT as per the ATF-55143 datasheet.

Another option might be to just fit the model parameters to the data I recall you posting elsewhere. The data for MCL's I_DS/V_DS curves is available as well:

You could use their S parameters to get the parasitic reactances, and maybe extract some more graphs to fit from an ADS sim if you have access to a license. Never tried this, though, so caveat emptor.

On another note, does anyone know how NMF is supposed to work for noise simulations in LTspice? The results seem wildly off (too large by orders of magnitude), but I can't find any reference as to which model it is even supposed to use (McWhorther 1/f noise plus broadband noise inferred from transconductance?).

? David

Thanks, I'll plug that in and see how it compares to a real part.

I'm using the SAV541 to discharge a linear-ramp capacitor, so the only parasitic of great concern is drain inductance. I can measure that with TDR and add it to my circuit as a discrete inductor.

The trick with grounded-cap ramps is to keep the early part clean, linear and not ringing. The faster the discharge switch, the more it all wants to ring.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics