That looks really nice. Low capacitances, dynamite transfer curve, nice pulsed current. Let's try some.
This looks similar:
The Fairchild gumdrop parts are mostly excellent.
This looks promising, too:
John
Tough to get though. Once I tried to cajole Infineon into samples of another FET, explicitly telling them that I don't want them for free, would also pay S&H and all that. They didn't afford me as much as a courtesy call back. Ditched them.
I had looked at those a long time ago. The turn-off times are sluggish yet they are driving them with gusto, for example Rgen 10V/10ohms for the Vishay. They are smacking a whopping amp into the gate. 10pF and
150ohms load doesn't explain 35nsec turn-off and I bet their marketing guys would razz them for being too conservative.But one never knows with FETs.
-- Regards, Joerg http://www.analogconsultants.com/
Looking at the 2N7002 data sheets, one would never expect the sorts of speeds I'm seeing. All you can do is get some parts and try them.
The ones that switch fast seem to have low Cg, modest Rds-on, and peak drain current ratings under an amp (which doesn't stop me from going above an amp.)
I recall Win Hill getting kilovolt edges in a couple of ns from fets that, from the data sheets, shouldn't do that.
John
"Test a lot?" What does that tell me? It went against my grain to use a green LED (GaN) at 3.3V. "Because one works..." Well, at least if the next lot doesn't work we'll know.
We buy modules for all that stuff. I wouldn't attempt it with the shoestring capital budget we're on (we're down a scope and it doesn't appear that they're going to even replace it).
...not that I have anything for the '7002, mind you.
[...]
I didn't mean a lot as in production lot, but as in "a lot of testing" :-)
Meaning some of the properties have to be measure. In some designs that is the only way to succeed because there are no parts that can "formally" do what you need them to do.
A scope? That's scary. I hope that doesn't mean any bad news. You can nowadays get a lotta scope for $1-2k.
[...]-- Regards, Joerg http://www.analogconsultants.com/
I have seen very zippy transitions from a 2N7002 myself. Not like yours but then again the fastest scope I have rolls off at 1GHz. Never seen a P-channel come anywhere close to that. There used to be a BSS83 P-channel that was very good. But it seems to be gone. Believe it or not, there is also a BSS83 N-channel from another European manufacturer. Whoops ...
Was that shortly before this happened?
-- Regards, Joerg http://www.analogconsultants.com/
But that means you need a lot of lots! ;-)
In my former life, we would specify what was needed. Sometimes it got expensive but the groundrules for such designs was "worst case". Life is much simpler now. ;-)
I don't think it's permanent bad news. I think it's more prudence, given the Obama recession. I really can't argue much. The scope we lost was a 300MHz model. The remaining one is only 100MHz (there is another but it's usually tied up with firmware stuff) and they seem to think that's good enough. Of course, I'm holding out for a MSO3034. ;-)
I really need other stuff, too. I'm going up to Atlanta for compliance testing on a design I know will fail ESD. It was never designed to pass (the JTAG port is exposed on an external connector) but the requirements changed at the last minute (well, the last week). I really need an ESD gun.
Maybe, after Obama gets the boot. ...or I retire again. ;-)
We don't need anything like that. Who looks at the carrier? ;-)
You can get a Tek 11801C and an SD14 plugin (3 GHz, with built-in FET probes) for $1k total on eBay. Of course that's a stroboscopic sampling scope and not a single-shot digitizing one, but it's beautiful for repetitive signals.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Good thing you have some Cg there to help clamp those kilovolt edges...Assuming they were short to begin with.
Jamie
Starting at a Ghz bw ?
Jamie
I'm not arguing that you aren't an expert electronic engineer, merely commenting on your persistent need to be *seen* as an expert electronic engineer, designing "insanely good" circuits.
Not that you'd notice.
So you don't get my jokes, and you interpret every critical comment as an insult. Maybe you are the problem?
I hadn't realised that I was so self-obsessed - I'll have to pay even closer attention to what I post about growing up in Tasmania and going to a better university than Tulane ...
I invented that back in 1986, for a retrofit to the Metals Research GaAs crystal puller. Back then their crystal pullers made 95% of the single crystal GaAs produced on our side of the Iron Curtain, and you've probably used some of the GaAs made in one of those machines. It has been oscillating for more than twenty years now.
-- Bill Sloman, Nijmegen
[...]
Yup. It pays to not always insist on the latest, best, tallest, most expensive gold-plated gear. I do have a GHz BW scope here but it is repetitive sampling, HP from the early 90's. Good enough for work and I do a very wide variety of projects, including pulse stuff.
I never felt the urge to own a 5-10 GSPS super-expensive scope. Sure, at times it would have been nice but I was always able to make a signal reptitive enough that the HP displayed it.
One does not need a Lamborghini to haul some stuff from town :-)
-- Regards, Joerg http://www.analogconsultants.com/
Makes no sense. Equipment is cheap, and people are expensive.
John
Or a Rigol, for $350.
John
Invest another $500 or so and get 20 GHz TDR.
John
happens
and
breath.
FET
You can't lay off a scope. ;-)
they're
That may be bit skimpy. I often find myself debugging and finding things on the digital side, where everyone was 110% sure it couldn't possibly be a software issue. That's mostly SPI and other serial buses where 2ch won't really work. Also, I found that 100MHz BW ain't enough. Glitches in systems where a 8051 screams along at 80MHz or so are specterally above that.
But IIRC there was that Dave Jones tuning :-)
-- Regards, Joerg http://www.analogconsultants.com/
[...]
they're
Sure you can. On Ebay. And the upside is the scope, once sold, won't turn around and serve you with a lawsuit about half a gazillion hours of overtime that the scope feels it should have been paid for.
-- Regards, Joerg http://www.analogconsultants.com/
shoestring
they're
That's been my point when management (and the other engineer) suggest that
100MHz is enough. Gotta have at least 3X, 5x is better.It's just so weird to see the words "8051 screams along" run together like that. ;-)
For SPI and particularly I2C, I'd really like to see both the analog and data domains, particularly for triggering.
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