Cell phone noise into opamps

Thanks. Yes, that's one large amp. We now have 8-TSSOP in there and it might not fit.

Mail me the schematic and layout, and I'll do some hand-waving.

John

The story is that B-B had a lot of old production test sets that have started to fail, and they can't get parts to fix them, and it will take a while to design new ones.

TI tech support has been atrocious lately. I suppose it's all backed up.

John

I've heard such rumors as well. What's so difficult about a test set? And why do they suddenly fail? Somehow it sounds like a management problem. I mean, it's been months now if not a year.

Lately I have become a bit more bold there. If a part is hard to get or support isn't forthcoming it's outta here. Usually for good or at least for a long, long time. Even if it has to be done discrete, so be it.

Then I'll get shot :-)

I already did the convincing session (thou shalt not split grounds etc.). The layout is going to be pretty good and with some extra shield cans and stuff I am sure we can make it work. But no matter how much filtering there comes a point where something without a b-e junction would be kind of nice. This is an app where a cell phone right next to the unit is something to be reckoned with. Almost like good ole mil stuff.

Just an observation:

These tiny Bluetooth headsets seem to get away with this sort of stuff. I have one which happily works without any audible interference with the cell phone sending Bluetooth data , and of course its own radiation at 8-900 MHz, with the phone effectively right on top of the earpiece. And its all in a plastic moulding.

It's ok for simple audio stuff. But we have to extricate signals in the uV region.

Digikey: Only 31 OPA627 left, in the classy TO can. Nice for a retro project but don't count on building more than 31 units. Sometimes I have the impression the time you were talking about has come. Lots of BB parts shortages.

The OPA656 is around 80nV/rtHz at 10Hz or as Archie Bunker would have put it, lousay.

Adrian Jansen snipped-for-privacy@qq.vv.net posted to sci.electronics.design:

I saw your frequencies and thought "that's not right". So i googled and the correct frequencies are 2400 to 2500 MHz pretty much worldwide. Right there with 802.11b/g network equipment.

Joerg snipped-for-privacy@removethispacbell.net posted to sci.electronics.design:

Given the recent purchase it sounds like an inherited management oops. Just the same, test sets should not be failing.

Joerg a écrit :

Oh, you can find consolation by looking at some CMOS opamp datasheet.

Hi Joerg

Does the circuit run on a single supply ? Try dual ! and separate 0V from shielding ground by a few Ohms.

Robert

It has dual supplies. Uncoupling anyb of the grounds makes things a lot worse, pretty much what I've always seen. That's usually because the source cannot be truly differential.

datasheets:

Just wondering, are the cell phones in question GSM T-Mobile or Cingular/AT&T phones?

Michael

datasheets:

We tried a lot of them and it was all over the map. Mostly CDMA I guess, at least none was from T-Mobile. Mine (Nokia 2115i on VirginMobile which uses the Sprint Net) was actually the most docile. A Verizon one really hit hard, so did a BlackBerry. But it'll depend on how far the next tower is and thus the ouput power it sets itself to.

datasheets:

Ah, ok. I thought the interference was predominantly from GSM phones.

"It is a common occurrence for a nearby GSM handset to induce a "dit, dit di-dit, dit di-dit, dit di-dit" output on PA's, wireless microphones, home stereo systems, televisions, computers, cordless phones, and personal music devices."

I had thought this was our car stereo going bad; knowing this now, it was most likely my wife's GSM phone.

Regards,

Michael

datasheets:

Yep, just had a thread in a German NG. Dits and grumbles in the stereo ever hour or so. One of the guys asked whether they had plopped the cell phone down anywhere close. Answer: Uhm, ah, well, yes! Problem solved.

I'd have thought *everyone* over there knew about that. They've been exclusively GSM for years in Europe.