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NNTP-Posting-Date: Thu, 16 May 2024 01:09:05 +0000
From: John Larkin <jjSNIPlarkin@highNONOlandtechnology.com>
Newsgroups: sci.electronics.design
Subject: Re: fast discrete PHEMT one-shot
Date: Wed, 15 May 2024 18:07:12 -0700
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On Thu, 16 May 2024 00:00:56 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> On 2024-05-15 12:47, John Larkin wrote:
>>> 
>>> https://www.dropbox.com/scl/fi/agatzclr8pvr5470g6mc4/Phemt_One_Shot_1.jpg?rlkey=cwnx0qd7ajgnh8otf627x5lku&raw=1
>>> 
>>> Regular monostables are terribly slow. This one has low prop delay and
>>> high rep-rate, if the sim is to be believed.
>>> 
>>> SAV541 is mostly specified as an RF part, but it's a dynamite switch.
>>> 
>>> I can post a link to the files if anybody wants to play with this. All
>>> my values are first guesses, no math involved, and it works!
>>> 
>>> My SAV541 Spice model is a revision of Phil Hobbs' original.
>>> Mini-Circuits is adamant that they will never provide Spice models, a
>>> typical RF-bigot attitude.
>>> 
>> 
>> With a low-resistance drain load like that, you don't care too much 
>> about the low drain impedance of the pHEMT.  The old Avago ones were 
>> around 160 ohms iirc.  The transconductance is high enough (400 
>
>millimho or 

Rds-on is about 2 ohms with a half a volt or so on the gate.

Interestingly, they seem to keep turning on harder with insane gate
voltages, like +1 or so. Ig is about 16 mA, way past abs max, at 1
volt, but I'll just pulse it so it will be fine. Right?



>> something ridiculous like that) that you get gobs of voltage gain even so.
>> 
>> Really really crappy for followers though!

Tell me about that. My triggered 50 MHz colpitts oscillator squegged
at around 4 GHz. Tons of jitter.

I designed a new osc using a BUF602 and it's great.