Does anyone know of a good substitute for the 2N2356 and 2N3082 chopper transistors. They're mentioned on page 90 of GE transistor manual, but appear not to be manufactured anymore. I'm tinkering around with a design that will require transistors in the inverted position.
relevant point on Mosfets, however my design is tailored around having Vbe's closely matched. I believe this is more difficult to do with Mosfets, although not to sure about Jfets.
Zetex makes some rather nice low sat dual transistors..try (in this order): ZXT12N50DXTA, ZXT09N50DE6TA, and ZDT1053TA. As far as singles go, the ZTX1048A, ZXT1049A, ZTX1051A, or FZT1053ATA. You will notice that i purposely picked high beta transistors; for lower on saturation voltage, run them inverted. Zetex seems to make a goodly bunch of high inverse beta transistors - which makes them better as choppers.
JFETs rock in this domain. The only MOSFET that I like in this area was a quad, the SD5400. But it has changed ownership and to me it's now too much of a boutique part. Digikey doesn't have it, expensive.
For us non-chip guys the main problem in the last 2-3 years is a whole different one: You have to be able to obtain the parts without a 40+ week leadtime. Seriously, that is driving a lot of design decisions these days.
Just got off a conf call with an IC design house and my client. Man, you guys have it easy. "Can we change the Rdson for the n-channel device over yonder to about 20% or less?" ... "Yep, sure, consider it done". All they do is type another number into the channel width attribute field. Now try that in the discrete world in the year 2010. Type in your part number ... out-of-stock ... type in another ... 22wk leadtime with no guarantees ...
All semiconductor parts are hard to get these days. We have lead times from 3 months to over a year. Hopefully, won't be like the late 90s when resistors and capacitors were hard to get.
As for CMOS switches, I've found Fairchild's FSA66 and FSA266 to be super duper. Somewhere around 0.05pc of charge injection.
0.05 pF is amazing, but that's measured at Vgen=0, Rgen=0. Do you have experience with more general signal levels? There are no graphs on the datasheets.
And status = obsolete!
Most of those logic-family analog switches have huge charge injections.
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