Hi Jinan,
In addition to Michael's suggestion, I found the following application note on the topic. Hope this helps.
https://www.ti.com/tool/TIPD147?keyMatch=SPECTRUM%20ANALYZER%20NOISE&tisearch=Search-EN-everything
https://www.ti.com/lit/ug/tidu016…
Hello Robert,
I had a discussion with one of our Precision Amplifiers Test Engineers, and one of our Product Characterization Engineers in an attempt to gain a more complete understanding how the OPA2189 noise is measured and characterized. I have a better…
A common method used to measure low noise circuits is discribed in the TI design given in the link below. The key is to follow your amplifier with low noise amplifier that will boost the noise signal to a level you can measure with a scope. If you provide…