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TI opamp

Am 12.03.2015 um 16:44 schrieb George Herold:

I did not see any microphonic pickup. But then, the preamp was in a alu cast box, the measurement object was also in such a box, Semi Rigid coax between the two boxes, everything on a staple of books and all together in a massive aluminium cargo box with BNC feedthroughs only. One of the books was Conelly-Motchenbacher on low noise design, to ask the gods for a good outcome. ANY connection of the preamp and the test object box in excess of the semi rigid resulted in a loop that filled the screen with spurious. Not _some_ spurious - Nothing BUT spurious. The baseline here is pV noise densities.

That isolation also helps against acoustics, and me, I'm quite quiet, so sorry, no microphonics seen. :-)

regards, Gerhard

Reply to
Gerhard Hoffmann
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Grin.. yeah the beauty and curse of a diode laser. Believe me I know all about this. (A bit ago I spent ~1 week measuring the 25C free running wavelength of 100's of DL's into a wave meter Jr. Whose back reflections is bad too. The back reflection "stair case" has lots of steps in ~1GHz, so ~100MHz. for a ~1m path length. Watching a spectrum seems like a good indicator.

Are back reflections a parametric amplification? So that below some threshold it's "mostly harmless"?

This is much smaller... it smells like a ground loop, shielding thing, which is harder, cause whatever I did ~10 years ago for grounding and shielding was f'ing around till it worked...

George H.

Reply to
George Herold

If you arrange the batteries antiparallel, for 0V nom output, the first stage could have a decent gain, 20x at least, and be DC coupled.

Every wire connected to a battery is a thermal antenna + thermocouple. You could get 10s of uV/K from a copper wire soldered to a nickel-over-steel end cap. Millikelvin temp fluctuations could generate some of the noise.

We've seen the same thing in crystal oscillators, in the 1 Hz jitter ballpark. You can really improve a cheap XO's jitter by covering it with foam.

--

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

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

I still don't understand. :(

How can fig.27 show the output is zero at 10MHz if the GBW is 110MHz? Should there not be *some* output at 110MHz?

Thank for your help.

Reply to
John S

There will be, but not much. With a slew rate of 22 V/us, the maximum undistorted sine wave is 22E6/(2 pi * 110E6) = 30 mV peak.

It's intended for audio, where that slew rate is much better than good enough.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Thanks, Phil. I think I understand now.

Reply to
John S

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