Si-based Sub-THz heterodyne imaging circuits

This paper presents an analysis to compare the heterodyne detection and the direct detection in terms of their noise performance, particularly for high frequency applications where low noise amplifiers can hardly be employed. The results show that the heterodyne detection provides superior noise performance, especially when a high gain IF amplifier is inserted before the IF detector. To verify the analysis, a sub-THz heterodyne imaging receiver has been developed based on 65-nm Si CMOS technology. It exhibits a noise equivalent temperature (NEP) as low as 0.9 pW/Hz^0.5 in absence of an RF low noise amplifier, experimentally verifying the excellent noise performance expected from the heterodyne detection.