Re: Bypassing

John Larkin wrote:
On Sat, 10 Jan 2009 16:12:43 -0800, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Sat, 10 Jan 2009 13:58:20 -0800, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Sat, 10 Jan 2009 12:58:29 -0800, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

John Larkin wrote:
On Sat, 10 Jan 2009 11:25:51 -0800, Bob Penoyer
<bob@xxxxxxxxxxxxxxxxxxxx> wrote:
[...]

This is a very unusual configuration. It suggests to me that the guy
who wrote the datasheet experimented and found that this configuration
worked for him when other configurations didn't--in his particular
set-up. Why else use the series resistor?

This suggests that the part has some stability problems that even the
applications engineer had a hard time dealing with.
This opamp has an 18 GHz *closed loop* gain-bandwidth product. It has
a right to be pickey.

And all that for under four bucks. TI came out with some great amps. Now if they only had piped out the IN- directly ...

That node probably can't be brought to a pin.

I was hoping pin 12 could do that with pin 13 VS+, but probably you are right, this can become iffy.


On our latest gadget, we aren't grounding the IN- pin, but bypassing
it hard and driving it from a trimpot + c-load opamp, to use it as a
DC offset trim. Wish us luck.

That's one of those situations where your new PADS guys can test his RF skills :-)
Girl. The Brat, in fact. Her first board was a 4-layer, 1.5 GHz, G=100
amplifier. Wish us luck.

So she did come back and join your company? Great! Or did she feel guilty about having bought that Jeep from, ahem, savings?

She's working for us now. She managed a pretty big programming project
(with a terrible programmer) successfully, and is doing a bunch of
marketing sort of stuff... ads, press releases, links. Apparently many
business schools require a couple of years of work experience, so she
may put in a couple of years here, then go for an MBA.

She really likes pcb layout, incidentally.

A lot of her classmates/teammates are still unemployed, or doing scut
work.

Maybe they should open up their search a bit. Back at my university you had to get a minimum of six months of industry work under your belt. Else no masters degree. There were times when such jobs were scare and I ended up working a lot in foreign countries. Gives a student a great boost in experience (but they may have to sit down and learn a language).



The best pcb layout people I've known were women.

I also worked with several women who were excellent layouters. But my current layouter is a guy, around 60, tons of experience. When we discuss an RF critical layout after giving him my schematic and netlist we usually talk about RF-tight areas for one minute and then another four about politics. Boards come out like clockwork and luckily we are on the same page in terms of politics :-)


The TI rep has told us that standard analog remains a very important
part of their biz. Looks like they got beat up on cell-phone parts
(huge volume, zero margin) so are going back to customers like us for
revenue. They do have the fastest 30-volt process on the planet.

Yes, and on one project I sure was glad they do.
Lest I repeat myself... do NOT use THS3062!

I never use CFB amps. When I need this kind of gusto I always go discrete. Much cheaper, too.

But how do you get analog precision from discrete amps? I mean
millivolt offset, <<1% gain accuracy, low distortion... and in a
reasonable size? I can see using discretes for open-loop, ac-coupled,
audio and RFey type stuff, but not for fast precision instrumentation.


If needed I use two tricks: Clamping for DC offset restore and controlled FETs for gain auto-calibration. But most of the time DC performance is irrelevant and then I often resort to PIN diodes for gain cal. If it has to be really cheap then stuff like band switches or something with a somewhat useful PIN characteristic.


CFB amps rock! Nothing else has that kind of slew rate. It's one
architecture that decouples slew rate from standing current.


Yeah, but clients got zinged a few times by availability issues and "not so favorable" pricing. However, for smaller volume production CFB could be the ticket.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
.

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