22.3 A 0.42THz Coherent TX-RX System Achieving 10dBm EIRP and 27dB NF in 40nm CMOS for Phase-Contrast Imaging

The small wavelength and non-ionizing nature of EM waves in the THz spectrum make this frequency band attractive for high-resolution imaging applications. While amplitudebased THz imaging systems have already been demonstrated in Silicon [1], an integrated solution for phase detection in this frequency range has not been reported so far. Detecting the phase change of THz waves passing through the imaged object would enable applications like high-precision thickness measurement and dielectric permittivity characterization. Furthermore, phase-contrast imaging techniques allow scanning of weakly absorbing materials, such as soft tissues and polymers, where amplitude-based scanners are incapable of providing clear pictures [2]. However, the mentioned applications demand high phase-detection accuracy, imposing strict SNR requirements on THz phase imagers for real-time operation. The main SNR limitation of such systems comes from the high NF of the THz receivers [3,4], due to the lack of an LNA prior to downconversion of the THz signal. This paper proposes a two-step IQ downconversion RX architecture with low-loss LO power combining as a way to alleviate the mentioned problem, achieving RX NF of 27dB at 420GHz. Additionally, it presents a frequencylocked TX that achieves 10dBm EIRP, leading to 52dB SNR (100kHz RBW) of the TX-RX coherent imaging system when operating at a distance of 25cm. This system demonstrates 420GHz phase detection with RMS accuracy of 2.8° and RMS 1σ precision of 1.7°.