Path: local-4.nntp.ord.giganews.com!Xl.tags.giganews.com!local-1.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Thu, 16 May 2024 01:09:05 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: fast discrete PHEMT one-shot Date: Wed, 15 May 2024 18:07:12 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: References: <88dc3fcf-7731-cc95-3bb5-80d5cbd6edc9@electrooptical.net> X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 44 X-Trace: sv3-ul5sb8EbocllSg6qz7aKLLOoSWhIInI8hbHYyhHBKTKnuPMfIKqDUC2PNOPPHspgwpix8il4UmV9atf!VZpirGeZguS4ZI+3Ejo97PoYfAABBz38+S0/zzLRZjgpJbJ9ZYhifBsM2xKCOegsP/Dq6CpMZX0b!1Ielrg== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 2874 On Thu, 16 May 2024 00:00:56 -0000 (UTC), Phil Hobbs wrote: >Phil Hobbs 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.