Cyclostationary Shot-Noise Measurements in RF Schottky-Barrier Diode Detectors

Homodyne (zero-IF) operation is very prone to low-frequency noise, partially contributed by the solid-state detector operated in large-signal (quasi-)periodic conditions. Shot noise is the major contributor to this noise if the detector is operated beyond its noise corner frequency. In this letter, we experimentally observe that the current spectral density of this shot noise in Schottky diode detectors is different from the conventional $\hbox{2}qI$, where $I$ is the average current. It is found that it varies as $\hbox{2}nkT/R_{ \rm dp}$, where $n$ is the diode ideality factor and $R_{\rm dp}$ is the small-signal resistance of the pumped diode that can be very different from the standard-diode small-signal resistance obtained from the differential of the $I$–$V$ characteristic. To the best of our knowledge, this behavior was anticipated theoretically a long time ago but has been seldom addressed experimentally.