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pHEMT model tweaked for 1/f noise

Hi, all,

In one post on the 'purpose of precision' thread, I noted that the ATF38143 model I posted awhile back predicted way, way too much low frequency noise. The real pHEMTs tend to have a pretty accurately 1/f PSD with corner frequencies between 10 and 50 MHz.

Their 1/f characteristic makes them pretty good for bootstraps, because the f**2 PSD caused by eN*C noise squashes the flicker noise pretty well.

Here's the old one:

.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)

The relevant parameters are AF, which is the reciprocal of the noise exponent, and Kf, which is the noise amplitude.

This produces a low-frequency noise PSD that goes as 1/f**2, and at 10 MHz is 340 *millivolts*/sqrt(Hz).

Here's the new one, with AF = 2, which gives a 1/f PSD, and KF = 5E-11, which gives a 1/f corner of 22 MHz.

.MODEL SAV551_chip 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've attached the .asc file to this blog post at .

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
Reply to
Phil Hobbs
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I posted a slightly expanded version of this post at , with a screen shot and the .asc file link.

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
Reply to
Phil Hobbs

That's wonderful. I have several active uses for SAV551, both linear and switching.

The thing on the left is a 551.

formatting link

I hope to finish that and fire it up tomorrow, if enough people will leave me alone.

I also have a new coaxial ceramic resonator oscillator that uses a

551, and I want minimal phase noise. 
--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

Your model is a bit off my DC measurements, which of course doesn't matter in most amplifier applications.

At +600 mV dc on the gate, I measured Ig = 2 uA and Rds-on = 2.2 ohms. Your model has more gate current and higher Rds-on, 230 uA and 5 ohms.

I'm driving some from 4 volt CMOS logic, high or low, through 5K resistors. Sort of like it was a bipolar transistor. The gate behaves a lot like the gate of an NPN. Like most such parts, the gate is delicate, rated 2 mA max for this one.

I might tweak your model a tad to make it a little better for switching.

Mini-Circuits does *not* have a Spice model for any of their phemts.

OK, time for my donut.

--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

Fun. Keep us posted.

Dunno if a device with a 20-MHz 1/f corner is what you want for that, but maybe.

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
Reply to
Phil Hobbs

My procedure was pretty simplistic--I just stuck 30 mA through it, measured V_GS, and hacked VTO to make the two agree. I ignored base current entirely.

Cake, bread, brioche, cruller, ...?

I cordially dislike cake doughnuts, but a good maple- or chocolate-iced bread doughnut is a beautiful thing.

Cheers

Phil Hobbs

(Pecan sticky buns rule, as long as they're not the toffee ones);

--
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
Reply to
Phil Hobbs

Probably not. I should probably use a fast NPN.

If you have any spare time, maybe you could help with this. Some thinking, if nothing else. I think I have invented a digital PLL that I don't understand!

(Want a new DDG?)

formatting link 

--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

Our nearby Safeway makes a super Boston Creme, white goo inside and cholocate icing. They make great bagels too. All their other baked stuff is terrible.

Sticky buns are wonderful, but hard to find here. We have "morning buns" that are awfully good.

The Brat is working on her Guinness Cake. She's bringing the latest revision over tonight for a design review.

--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

Have you tried basing it on the ADS-style quadratic Curtice model for the ATF-55134?

Something like (with your noise parameters)

.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, Kf=5e-11, Af=2)

although that Vto looks a bit odd; definitely needs fiddling to make it match measured parameters.

? David

Reply to
David Nadlinger

Sounds like fun. Send me an email.

Very nice. More modern looking than VFDs, though not as pretty a colour.

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
Reply to
Phil Hobbs

That place down the hill from you, across from the used record store, had very good sticky buns.

Could make a mess of your git repos. ;)

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
Reply to
Phil Hobbs

I'd have to actually figure out what all those parameters do, though. ;)

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
Reply to
Phil Hobbs

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She invented the multilayer Guinness Cake. It doesn't relly look like a draft Guinness any more, but the icing/cake ratio is advantageous.

--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

Oh. I thought you knew.

--

John Larkin         Highland Technology, Inc 

The cork popped merrily, and Lord Peter rose to his feet.  
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
Reply to
jlarkin

I did read up on the noise and threshold parameters for maybe 10 minutes. I might hook one up to the HP 4145B when I'm in the lab next week--we're using a SAV-551+ bootstrap for a new photomultiplier-replacement gizmo. In certain frequency ranges it's a super good bootstrap, so it might be a good idea to try to generate a better model.

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
Reply to
Phil Hobbs

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