The Siliconix PAD1 at 1pA and 0.8pF is still available : http://www.micross.com/pdf/LSM_PAD1_TO-72.pdf
On Sat, Apr 8, 2017 at 4:52 PM, David <davidwh...@gmail.com> wrote: > On Thu, 6 Apr 2017 22:23:43 -0400, you wrote: > > >David wrote: > > > >> I know one thing to watch out for if you are looking for low > >> leakage is gold doping > > > >Anything that increases carrier mobility increases leakage current (all > >else equal -- i.e., for each particular device geometry). This accounts > >for the much higher leakage of Schottky and germanium junctions. > > I mentioned this in connection with some manufacturers using gold > doping in transistors which would not normally be expected to have > gold doping. So you end up with a bunch of lessor named 2N3904s which > meet the 2N3904 specifications but are useless if you were looking for > low leakage diodes. > > >> And I have another question if you know. How is rb'Cc measured? > > > >One way is to drive the transistor with a medium-high frequency (well > >down the 1/f portion of its current gain curve -- typically 10-50MHz for > >small-signal BJTs) and measure the base-collector phase shift. It can > >also be calculated from fT and Cc-b. There is a JEDEC standard for > >measuring rb'Cc, but I'm not finding my copy at the moment. It may be > >posted on the JEDEC web site. > > I thought there was a more sophisticated way but that sure sounds like > something Tektronix would have done for grading parts. > > The JEDEC standard is probably what I need to find or at least start > with. Thank you for the tip. > > >> The advantage of the 4117/4118/4119 is that the leakage is already > >> tested to a given specification so no qualification or testing is > >> necessary. > > > >That may be true, but there is nothing in the data published by Vishay, > >Fairchild, Calogic, or InterFET to indicate this. Spot-checking, along > >with the part design, should be sufficient to guarantee meeting the > >spec. I'll try to remember to ask the Vishay process engineer next time > >I talk to her. > > > >Best regards, > > > >Charles > > If they are not being tested, then where is the maximum specified > leakage number coming from? For a small signal bipolar transistor it > will typically be 25nA, 50nA, or 100nA, but the InterFET datasheet (1) > shows 10pA maximum and 1pA maximum for the A versions. > > When this discussion of low leakage input protection started, I did a > quick search for inexpensive alternatives to the 4117/4118/4119 JFETs > and came up with nothing; all of the inexpensive JFETs are much worse > until you get to premium devices. > > (1) I only picked the InterFET datasheet because it was the most > readily available of the ones you mentioned. The current Fairchild > and Linear Systems datasheets show the same thing. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
