300-GHz Direct and Heterodyne Active Imagers Based on 0.13-μm SiGe HBT Technology

300-GHz direct and heterodyne imagers based on a 0.13-μm SiGe HBT technology were developed for active imaging applications in this work. The direct imager, which is based on the square-law principle, shows a maximum responsivity of 6121 V/W and a minimum noise equivalent power (NEP) of 21.2 pW/Hz^1/2 at 315 GHz. The heterodyne imager, which consists of a mixer, a local oscillator, an IF amplifier, and an IF detector, exhibits a maximum responsivity of 322 kV/W and a minimum NEP of 3.9 pW/Hz^1/2 at 300 GHz. Total dc power consumption of the direct imager is 0.6 mW, while the heterodyne imager consumes 21 mW. The chip areas of the direct and heterodyne imagers including the on-chip antenna are 460 × 410 and 610 × 610 μm², respectively. To compare the performance of the two types of imagers for imaging applications, images from both imagers were acquired and compared with various output power levels of the signal source. It was demonstrated that the heterodyne imager shows much better image quality, especially when the signal source power is not sufficiently high.