SPICE gets it wrong

I mostly use BJTs as transconductance devices, and their nice repeatable turn-on is a big plus. They're also much better in low-voltage analogue stuff for the same reason. Besides being much, much quieter.

PNPs are good for positive-to-negative level shifting, too.

Those SiGe:C devices (BFP640/650) are magic--high beta, low noise, effectively infinite VAF, and bandwidth that goes on forever. As you pointed out some time back, they don't switch as fast as pHEMTs that are seemingly slower. That one-diode sampler I did with ChesterW last year originally used a BFP640FESD, which produced a 200-ps sampler. Swapping it out for an ATF55143 got us down to 100 ps, but cost an extra 45 cents ($0.67 vs $0.22).

Cheers

Phil Hobbs

Nah nah it was an _isdn_ xfrmr. That's the good s*it

Where's Famous Chef Pante?

ISDN transformers are really cool; I've used lots of them (over 20K!) in power supplies and such. My favorite part is 1:1:2:2, which is pretty versatile. But I use home-made transmission-line xfmrs for big fast pulses.

Is ISDN still alive? "It Still Does Nothing"

The problem with fast bipolars, especially PNPs, is that they keep getting EOL'd.

I'm planning to get a few reels for insurance pretty soon. BFP640s are too useful to lose, and they're only 20 cents or so--just like a BF862.

A couple of dollar's worth of fancy transistors can let me build a very swoopy box that sells (hopefully!) for $2k-ish.

Cheers

Phil Hobbs

We both sell IP, soldered to PC boards.

One of our customers wants to audit our parts cost to see if we're making too much money. We declined.

I know it was "Big in Japan" for a while...

I think it's still used by some businesses for POS applications and stuff. The wiki says Verizon no longer offers it in the Northeast as of 2013

BJTs are really more like voltage controlled current sources with a pathology than current controlled current sources

Bwahahahahahaha >:-} ...Jim Thompson

There have been analog designers with a lot more experience than I have that've said much the same thing.

The Ebers-Moll equation relating Ie to Vbe says nothing about Ie dependence on base current.

Gummel-Poon charge-controlled model is useless outside of computer simulation

And with much more gain than MOSFETs!

I like to think of low-Vce(sat) transistors as "MOSFETs with 5x more gain but a really leaky gate". They have a reasonably linear (including 3rd quadrant) "Rce(on)", too.

"Vbe(th)" is also way more repeatable. I was testing almost a hundred boards, recently, and measured a current-limited output on each of them as part of the test spec. The design is guard-banded, so the current limit is high enough never to matter in normal operation, while it's also low enough to dissipate a safe amount of power when shorted. Despite the wide design tolerance, they all measured within 0.3% of each other. (Evidently, room temperature was pretty stable between those days of testing.)

Tim

On a sunny day (Wed, 10 May 2017 16:16:56 -0400) it happened bitrex wrote in :

Well, maybe you misread the label, and it was a FET... :-)

On a sunny day (Wed, 10 May 2017 11:30:14 -0400) it happened bitrex wrote in :

Na, was in the kitchen just now baking mushrooms... MY opinion on this, and actually last night there was, on cable here, a professor giving college about CERN comparing it to a super microscope. You know ever higher energies needed to take a picture of ever smaller things. But if you ask me, I did say: 'Do you really expect to get a deeper insight into the Tesla autopilot software by driving those into each other at 1000 km/h?'

So..

Ya, I suppose if you could design a transconductance physics box with an exponential law instead of square that also had a pretty well-defined "gate" threshold of 0.6 volts and drew no "gate" current, there would be little reason to use anything else assuming similar noise performance over a similar bandwidth.

I think (x)HEMTs come pretty close, sadly they are not literally a dime a dozen and likely never will be.