Other Parts Discussed in Thread: OPA2209, TIPD147, OPA2140, OPA2192
I wonder how you are measuring the noise spec for the OPA2189
Unfortunately, I have not been able to get near the specified numbers when using it in a differential amplifier. I do get 30nv/rtHz or so, at 1khz and referred to input when I expect less than 9. Non inverting inputs are tied to ground. I tried various gains, from 4 to 21. No difference. Replacing the chip by an OPA2209, the only decent high voltage amp I had on hand improves the performance considerably, so it looks like it is something from the op amp itself. I tried several different 2189 with similar results.
And, by the way, I get what I expect when I test a low voltage low noise self correcting op amp like the CS3002 with the same setup.
For your information, I am using a SRS SR1 analyzer to measure the noise.
What is wrong? Am I missing something? On paper, the 2189 looks like it will improve our products but the test results, as they are, do not look good.noise test.pdf