I am comparing Analog/Linear op amps (along with some by Brand X) using the NOISE analysis of LTspice. The context is: single supply via 9V battery, high source impedance, low bandwidth needed (-3dB at 20KHz would be fine).
When I test the LT1464 against other models such as LT1006 and LT1112 I find that its noise at 1K is higher than either part and higher than the specs suggest to me. (Yes I know the LT1464 is dual and the others single).
Compared to LT1006, LT1464 voltage noise density is similar and current noise density is MUCH lower in the LT1464 (at 0.4fA), yet noise is slightly higher as shown below.
Based on my reading of several excellent Analog papers on op amp noise I expected that current noise density would dominate because of the 200K source resistance, at least until current noise density of the amp is VERY low, as with the LT1464. And if current noise is sufficiently low then resistor noise would dominate, which I have eliminated by the 'noiseless' spec. Yet if op amp voltage noise becomes the dominant factor then why are LT1006 and LT1112 very close in LTspice-reported noise when LT1112 voltage noise density at 1K is almost half that of LT1006 (22nV vs 14nV)?
These are the analyses for the tests:
I am very eager to understand these apparent contradictions.