Phil might like this one:
This is a 1 nv-noise-class opamp with a 1 Hz 1/f corner. It doesn't seem to be a chopper, but that may be hidden inside. Input noise current is fairly high.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Chopper. The noise density plot gives it away @ 100kHz-10MHz. But still pretty impressive to my somewhat chopper-naive eyeballs. (I've never had to fool with truly tiny signals.)
Cheers, James Arthur
Huh, wouldn't a chopper be peakier? I was thinking it could be shot noise from some gain stage * some resistance. It would be annoying if you wanted to use it past 100k Hz.
George H.
That does not look like a chopper, more like the usual noise peak that plagues 3 stage opamps. The LT1028 has it at 300 KHz. ADA4898 and AD797 do not have it.
The input stage must be run at high current to get the low voltage noise. That brings high current noise automatically.
I have made a low voltage noise amplifier (220pV/rtHz) by paralleling
20 opamps (10 ADA4898-2 pairs). The current noise is awful. But that's not bad if the input source is low impedance.cheers, Gerhard
It must have a bias-current-cancelling input stage, like the LT1028, which has 25nA input-bias current, but likely 250nA actual base current, making about 1pA/rt-Hz noise (see AoE pg 327). Adding a trace for the L6018 on the integrated voltage noise graph (Fig. 5.54 pg 338), shows that it's pretty close to the LT1028, and not much like the other choppers. Also, adding pencil traces on the voltage- and current-noise density graphs (Fig 8.60, pg 528), shows it coming close to matching the LT1028. Yes, all three plots do show better 1/f performance. But I suspect it's not a chopper.
--
Thanks,
- Win
It looks like giant NPNs in the input stage, with very good Ib cancellation and trimming. Input capacitances are high. The noise hump does resemble the LT1028.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Looks awesome. I'll try putting it in a compound-amp loop with an LM6171 and see how it works as a 100X instrument amp. My HP89441A is supposed to be here Tuesday, so that'll come in handy.
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 https://hobbs-eo.com
Yes, input capacitances are higher than the LT1028. Lowering the current density helps to move the 1/f break point lower. Too bad it doesn't come in a TO-5 package. I sawed the top off a metal-case LT1028 to get the die photo in Fig 8.59 page 527, look how big the input transistors are there.
--
Thanks,
- Win
I said "chopper" because somehow I thought I saw no 1/f rise, and thought the 200kHz-15MHz band was 1/f heterodyned up with some fancy hardware, maybe spread spectrum-ish. But, looking again there it is, 1/f right where it should be.
Rats. I am duly chastened.
Yes, and thanks for posting those.
Cheers, James Arthur
Seems unlikely. None of the noise plots on page 7 of the data sheet suggest that to me - pseudo-random chopping waveforms can spread out chopper noise, but those curves are pretty smooth.
The simplified schematic on page 11 certainly doesn't suggest any chopper element.
-- Bill Sloman, Sydney
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