Cross Correlation Measurements Of Thermal Noise With Cooled Transformers
Jian Wei · AIP conference proceedings · 2006
Most measuring equipment adds its own noise to the thermal noise of the sample being tested. Because it is also correlated, this intruding noise cannot be separated from the sample’s noise by cross correlation. With an improved algorithm for cross correlation, we were able to estimate the intruding noise added by the transformer‐amplifier combination. The dominant source of the added noise was found to be the transformer, and was further identified as arising from the core resistance of the transformer, instead of from the winding resistance. Using cross correlation with cooled transformers, we obtained noise temperatures less than 1 K for sample resistances from 1 to 10 Ω.