A 420-GHz Sub-5-μm Range Resolution TX-RX Phase Imaging System in 40-nm CMOS Technology

This article presents a 420-GHz phase imaging system designed in a 40-nm CMOS technology. It consists of a transmitter (TX), based on a multiplier chain, and a receiver (RX), based on a two-step IQ down-conversion. Those chips share an external, 17.5 GHz, reference to secure frequency synchronization between them. To increase the overall system signal-to-noise ratio (SNR), the TX is modulated with a low-frequency sine-wave signal, while a two-way LO power combining is implemented for the RX first mixer. Those techniques result in a measured TX effective isotropic radiated power (EIRP) of 10 dBm and RX noise figure (NF) of 27 dB, leading to the overall SNR of 52 dB (at a distance of 25 cm and a resolution bandwidth (RBW) of 100 kHz). Furthermore, the measured phase-detection root-mean-square (rms) 1σ precision is equal to 1.7° (on a 400○ range, at a distance of 25 cm and processing time of 500 ns), which leads to 3.4-μm range resolution. In addition, the system operation is illustrated in two imaging demonstrations, recognition of the printed text on paper and 3-D imaging. Those demonstrations illustrate the potential of the presented system and terahertz (THz) phase imaging in general.