Buffered FET logic, Direct coupled FET logic tutorial

Google "74HC application note". 74HC is always buffered (but there is the occasional 74HCU which is specifically unbuffered). Ditto for 4000 series logic, CD4001BE is buffered, -UBE is unbuffered.

Tim

-- Deep Friar: a very philosophical monk. Website:

Like GaAs DCFL, the GigaLogic stuff? That was depletion load, I think, like old-old NMOS stuff. Power hog.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Yuck, GaAs logic. It sounds like a good idea, until your signal has to change back.

Silicon PMOS aren't terrible, good enough to make high speed CMOS with. They're almost impossible to find discrete though. I haven't been able to find a P type 2N7002 for the same price.

The suckiness of PFETs is directly related to the bandgap. Silicon is moderate, so PFETs are okay. GaAs and GaN make s***ty PFETs. I can only imagine how poorly SiC and diamond PFETs will work, when they come along. I suppose they may already exist in the laboratory, I don't know. Curiously, this seems to imply that Ge-CMOS would be quite nice indeed, but the leakage is something else.

Tim

You mean PMOS as in P-channel MOSFET? Is that enhancement mode? There are certainly quite a few P channel enhancement mode MOSFETs around, I tend to use the BSS84 as a P-channel equivalent of the 2N7002. They are pretty close in price, certainly not significantly more, and multi-sourced.

I didn't see BSS84 on Mouser's search. Ha, figures, the cheapest entry doesn't have any characteristics:

I suppose I could try arguing "multi-source" as well, since there's only a few that are near that price range AND in stock (to bend the meaning of "source" to mean "cheapest parts only"..). Sure, there are lots in stock, but they seem to average $0.30 in hundreds, which is just silly for an SOT-23.

Tim

The old argument against Ge was that it doesn't have a good oxide--GeO2 is water soluble. Nowadays that isn't such a big worry, since high performance FETs don't use SiO2 gate insulation anymore--at least not in logic.

Do you have a reference for the PFET performance vs bandgap? InGaAs has a much lower bandgap than GaAs, but its hole mobility is similar.

(Not busting your chops--it's an interesting correlation if true.)

Cheers

Phil Hobbs

FDV302 is 5 cents by the reel. The n-ch version, FDV301, is 4.8 cents. Both are logic-level SOT23 mosfets, nice little parts, usable with 3.3 volt drive.

John

Nice, and low threshold voltage too. The FDV301 N channel is particularly good. Thanks for pointing them out!

Mark.

You can get BSS84 for somewhat less than 11c:

Also in Newark

Mark.

Oops, some of those not in stock. This always happens when we come out of recession. The reason for non-stock is allocation problems, the prices of anything left in stock might go up accordingly. Still it looks like BSS84 is roughly the same as 2N7002 if they were.

Mark.

Not performance directly, but it all comes back to mobility, and it's well known that holes move slower, especially in higher bandgap materials. A scatterplot could be interesting, but I don't have a big table of semiconductors (especially all those funky compound semis like CdTe, etc.).

I'm basing my assertion on the one semiconductor physics class we had, which used the textbook, _Solid State Electronic Devices_, 6th ed., Streetman and Banerjee, Pearson Prentice Hall (2006). There's a table in Appendix 3 (p.540) that lists bandgap, electron and hole mobilities, and some other things, for a number of semiconductors.

Chemistry is like politics. Generalizations don't work...

Tim

"Come out of recession" ?

Isn't CMOS logic FETs??

FETs and anti-FETs. ;-)

Does uncle FETster of the Adams family count?

Boki, is that you? :-)

Two of my favorite Boki posts from the golden oldies section:

Tim.

A pun as woeful as Wednesday.

He was a point of light whenever the power was out.