TI opamp

I'm surprised they support Tina. Nobody ever talks about using it, except Robert (THE Robert).

Tina is TI's counter to LT Spice.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

I need help understanding this: How can an op-amp with an output shown on fig.27 of the data sheet be zero at about 5MHz when it has a GBW of

110MHz?

That's the slew rate limit, which is low for this amp. That saves power but limits it for some appplications.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

OT, related:

I use it. It works well for simple things like sequential filters and anything that can use fairly simple models.

Except that it's closed. You have to buy the real deal to use non-TI SPICE models. Even though I use TINA-TI, it's not worth paying for the real thing (did that in the last job).

Nice write-up, thanks. Nice amplifier. Surprising how much 'noise' batteries make at 50Hz. ;-)

Cheers, James Arthur

e

alBatteries.pdf

That is nice... Gerhard, I wonder if you say any microphonic pickup in the batteries. Back in grad school we used 9V transistor batteries to bias a b olometer, a few uA of current. (Low temperature FIR sensor.) There was th is extra noise sometimes that we eventually traced back to microphonic pick up in the batteries... (If you talked loudly next to the battery bias box y ou saw the noise on the scan.)

George H.

All the batteries have similar curves, especially at low frequencies.

Is there any chance that the presence of DC increased the preamp noise? It wouldn't take much leakage in the input coupling cap to upset the preamp. I assume the preamp is a bunch of paralleled jfets.

Some simple tests could discount that possibility. It looks like the Tadiran is the lowest voltage and has the least noise below 1 Hz.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

The preamp was massively paralleled ADI op amps (in the previous reference).

Cheers, James Arthur

OK, but there must be a biggish DC blocking cap. [1]

One easy test: connect 4 batteries in series adding, nom 6 volts, measure noise. Then connect them series opposing, nom 0 volts, repeat.

That assumes the noise is uncorrelated between cells. That's not true for thermal effects, and batteries have relatively huge TCs. So mummify them in bubble wrap an see if that changes anything.

[1] leakage in capacitors is non-metallic, so the electron ordering effect of metallic conductors is not present. So maybe capacitor leakage has shot noise.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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I was interested in the coupling caps. In his first paper (about the pream p ) He first used 16 10uF X7R ceramics (50V 1206), (160 uF and 10k ohm), he t hen switched to mylar.. but too big so went back to the ceramics.

I've got noise problems of my own at the moment. I was testing some new mi rrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum.

Here's a slow scan through the F-P transmission.

The first two are the noisy laser controller, (TEK00, TEK01) the last two t he old demo version. The width is only a few MHz, so just building shake g ives me a bit of jitter on the spectrum.

George H.

What's the span?

Looks like mode hopping to me--you wouldn't have those sharp jaggies if it were FM noise--the sidebands would have at least the same width as the carrier. Small differences in the temperature and bias current can change that.

Wolfgang's Laserblog has a bunch of interesting plots of noise vs T and I.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

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reamp

he then switched to mylar.. but too big so went back to the ceramics.

w mirrors in a Fabry-perot cavity and discovered that our diode laser is no isy. Grumble... I think it's current noise.. at least there is all this "n ew" interference peaks on the spectrum.

=0

wo the old demo version. The width is only a few MHz, so just building sha ke gives me a bit of jitter on the spectrum.

Hi Phil, I don't think it's mode hopping... it would be much worse. I can get feedback from the F-P cavity, but I monitor the transmission thro ugh an Rb cell and that spectrum stays clean.

It's a confocal F-P cavity, FSR = 385 MHz, (20 cm radius), with a finesse of 100 - 150 or so.. depending on how well I set the mirror position.

So the width of the transmission peak is 3-4 MHz.

It looks to be current noise..interference from somewhere. (Well I see current noise from the noisy unit and not the other.) Though I want to make sure of that before I start drilling down. I also wonder about noise on piezo drive signal... Grumble, one good way to ruin my day. My bigger concern is that there are other "bad" units out there that we'll have to recall... but I'm getting ahead of myself.

George H.

Hmm. Yes, ordinary mode hopping would make it a lot wider than 3 MHz, that's for sure, but those spiky things can't be ordinary noise sidebands, because genuine sidebands couldn't be narrower than the main line.

I suppose it could be acquiring and then losing self-lock on the cavity, which can happen pretty fast. What does the AM noise look like? Does the shape change when you change scan speed?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

preamp

, he then switched to mylar.. but too big so went back to the ceramics.

new mirrors in a Fabry-perot cavity and discovered that our diode laser is noisy. Grumble... I think it's current noise.. at least there is all this "new" interference peaks on the spectrum.

dl=0

two the old demo version. The width is only a few MHz, so just building s hake gives me a bit of jitter on the spectrum.

f n

through an Rb cell and that spectrum stays clean.

esse of 100 - 150 or so.. depending on how well I set the mirror position.

There is no lock on the cavity (F-P or diode laser). The F-P is not scanab le, just some mirrors in a tube. We scan the laser through the FP cavity m odes. If I scan the laser faster all the spikey things just happen on a fa ster time scale.. I only see a few in a pass through one FP mode. It's no t like there is excess broad band noise, but more like 1/f or increased int erference, pickup. Anyway first I've got to eliminate the piezo electronics as the noise sourc e.

George H.

Diode lasers have a strong tendency to lock to any stray reflection--almost like a phase-conjugate mirror with gain. You can make unintentional ECDLs really easily unless you have a whole lot of attenuation or a couple of stages of isolation.

Cheers

Phil Hobbs

Am 12.03.2015 um 16:51 schrieb John Larkin:

Not really. Scott Wurcer (father of the AD797) spotted immediately that some are much worse than 1/f. Having read Rubiola in the meantime: that must be simply drift. Rubiola has done a similar preamp using 3*MAT02 or sth. like that.(1)

The preamp is 20 parallel ADA4898. Input capacitors are ~22 10uF WIMA foil capacitors; I could not get more of those I had made the layout for, only mechanically bigger ones. So I glued them dead bug style onto the board, connected them with wrapping wire and hid them under the merciful cover of the Hammond alu box. :-)

I have made a next generation layout, but since the old one solves most of my problems, it is questionable if I ever will build it.

Ok, it seems to be long-time stable, but the 1/f corner is ridiculous. I bought it as a replacement for my 8970B noise figure meter, so I did not check it under load. That test would eat up some years of 8970B operation. BTW the Li battery came from Digikey in an extra box; it seems it must not fly on a plane that carries passengers also. I wonder if a noise figure meter is allowed to fly on a passenger plane.

For me, NiCd rulez, and size matters.

And, at 0.1 Hz, the coupling capacitor begins to isolate the preamp array from its badly needed low source resistance. So the noise current starts to play a role down there.

But I'm not really sure if it pays to push the lower frequency corner that much. Most test objects have a much higher 1/f corner than the ADA4898 and accepting a higher pole and computing it away would probably result in a better, not a worse dynamic range.

(1) Enrico Rubiola, Franck Lardet-Vieudrin : Low flicker-noise amplifier for 50 ? sources

(2) Enrico Rubiola, Claudio Francese, and Andrea De Marchi: Long-Term Behavior of Operational Amplifiers

I think his web site is rubiola.org, I'm just in the middle of nowhere and have barely cell phone reception, so I cannot easily search the urls. A _lot_ of stuff is there for timing-interested people.

regards, Gerhard