A 19–34 GHz SiGe HBT square-law detector with ultra-low 1/f noise for atmospheric radiometers

This paper presents the design, optimization, and characterization of a square-law power detector for heterodyne millimeter-wave radiometers implemented using 0.13 μm SiGe HBTs. A 3-dB bandwidth of 19–34 GHz (56% fractional bandwidth) is obtained through the use of inductively degenerated SiGe HBTs with large emitter lengths. The detector achieves a minimum noise-equivalent power (NEP) of 0.49 pW/VHz at 24 GHz with a peak responsivity of 17.1 kV/W. Through careful transistor biasing and judicious use of resistors, the detector achieves a measured 1/f noise corner frequency of 24 Hz when biased for optimal NEP. To the best of our knowledge, this detector achieves the widest fractional bandwidth and best 1/f noise performance of all tuned transistor-based square-law detectors for high-frequency radiometers to date.