Hi all, Well the opa124 is EOL, suggested replacement is opa145.
Anyone looked at used this opamp? I'm going to order a few.
Thx George H.
That datasheet raises the hair on the back of my neck. The amount of marketing specsmanship is even higher than usual, and there's no discussion whatever about the rising noise characteristic. With a 5-MHz GBW and a noise spectrum that rises starting at 10 kHz, there's a lot more high end than there is low end.
The OPA140 looks much better behaved. (I like it a lot, myself.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
The opa140 does look nice. In this case I'm replacing the EOL opamp in an old photodiode TIA. If I put in an opamp with 'better' GBW, then I think I'll have to change all the feed back cap values... so I'll give the opa145 a look-see.
Figure 39 seems to indicate that there is no noise hump out beyond 10 kHz.. but who knows.
George H.
That's the one that put me on guard--they don't tell you what frequency it's done at, but one gathers that it's 1 kHz or thereabouts. They are most mousey-quiet about what happens at other frequencies. Unimpressive.
Cheers
Phil Hobbs
(Coming to you from beautiful San Miguel Island in the Azores)
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Huh, I'm not paid enough.
So this is a bit of an aside, but I need a new gig*. There's a local defense contractor with jobs... I should talk with the people I know who work there, (I'm going in with an attitude that I'll hate it... not good (!), but with the 'right boss' it could be OK.) A small company would be better for me.
So as I'm walking around (beer in hand), thinking about tomorrow. And I think, my last teachspin project should be a Phil Hobbsian upgrade to the photodiode preamp... Out with this crappy opa124 eol opamp. It's a big area PD, (PIN-44D ?) ~100's pF C-diode at zero bias, ~1-2uA of photo current (there is ~2-3 uses so the specs vary...say 0 to 1 mA :^)
I've done a driven shield, (bootstrap) with an opamp. (can I do a dual opamp circuit to drive the back end of the PD?) So I was going to play with the 'cascode' input.
and then my 'linked in' profile?
George H.
*my boss wanted me to post here (on SED**) that teachspin is looking to hire another 'phd level' physics person. If anyone is interested,**cause I told him ~90% of my circuit fixes come from here. Hey if/when I do land a new gig I'm figuring SED will still 'have my back' circuit-wise.. I would really like more local wisdom, I'm mostly stuck near Buf. NY. (kids) for another few years.
What's wrong with your present gig? You seem to be doing well, doing interesting designs and helping to create new teaching products, what's wrong with that?
--
Thanks,
- Win
ISTR something about not being paid enough. I remember vividly having three kids in college at the same time. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Yeah on paper it's my perfect gig. In practice... I guess we have to be talking person to person, for the dirty laundry to be discussed. The bottom line is that almost all my present day collaboration, happens here (SED) and not at work. Which sucks*. I need a job where I look forward to going into work each day, for reasons that are ~1/2 my fault, that's not true anymore.
George H.
*there's a double suckage, that goes with leaving, and knowing things will be worse for all the friends and coworkers left behind. They are all friends and will understand, but the double suckage remains. GH
I didn't have such a dilemma. I got fired.
No TBH, the amount of money is not that important. There is certainly a part in where the profits are being spent.
My boss (who works ~ for free and I'm not counting) wants to hire a 3rd Phd. we'll have more phd's than production people...! it just seems crazy to me. (If anything we need more production people.)
George H.
Hah, I got fired too! we'll we need bar stools to discuss the details.
Maybe just a delayed fuse on my part.
George h.
Being fired was great. Started my life over.
Mine too.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
I designed $200M worth of electronics for them, and then they fired me for insubordination. The idiots didn't understand that engineers are supposed to be insubordinate.
Of course. Human resources are fungible. (Aren't they?)
Whatever happened to the "personnel department"?
We don't have one.
Right, that's what it feels like. I've always been a late bloomer so my mid life crisis can be a bit late at 60. :^)
If you are not working for yourself, then its's a matter of finding the right boss. (who wants you.)
The worst part will be separation from my current place of employment, I really hate conflict.
I've always wanted to be the 'lab guy' at some college/ uni. which are 'liberal crazy*' these days, and I sorta shudder at having to conform.
George H.
*crazy = authoritarian
As soon as I get a new gig I can talk 'on the air'.
So let me ask you this, we're bringing in phd's for a hire, my inclination is tell them my situation, after which I'm totally fine with them taking the job. (but could scare 'em off... cause no one wants to maintain my old circuits, including me. :^)
George H.
Well indeed the oap145 has voltage noise that rises by about 6dB by 100kHz. Though it appears to flatten off there and not go any higher.
Folder with 'scope Q-FFT's and SRS 730, these pics are a bit cryptic and I'd have to explain them... well the srs one is fairly obvious.
George H.
Dang you can't see those 'scope displays at all. (John L. how do you take such nice screen shots?) So for me, the 1MHz Q-fft* The fft is 4 dB per div,
500 kHz span and 250 (246?) kHz center freq. (The noise looks to peak/ flatten at 150-200kHz.) 100kHz band width is noise into same up stream amp but with 100kHz 2-pole, ~Q=0.707 LP filter. 10 dB/ div. Same freq scale.The SRS is it's max BW 0-100kHz and ~1000 averages (the Q-fft are also 1024 averages.)
George H. (*with a Q-fft you have to divide the power scale in half. you can do the math, or check it with a known filter and a noise source.) (my colleague 'did the math' for me.. I can post the relevant section of the manual if anyone wants.) And there is an interesting question with how small a coherent signal you can see.. 'buried in the noise' say in some given time. (to make a Qfft you've got to trigger near the top of your noise + small signal.. you get more 'small signal' triggers with a higher trigger level, but less number of traces to average. Does it go as the time squared, compared to a system that does the FFT and then averages that?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.