Dual-Terahertz-Comb Spectrometer on CMOS for Rapid, Wide-Range Gas Detection With Absolute Specificity

Abstract

This paper describes the design and implementation of a 220–320 GHz spectrometer consisting of a pair of 65-nm CMOS chips. The spectrometer utilizes two counter-propagating frequency-comb signals to seamlessly scan the broadband spectrum and significantly reduces the total scanning time through high parallelism. The comb signal, with ten equally spaced frequency tones, is generated and detected by a chain of inter-locked transceivers on chip. The large reduction of required tuning range for each transceiver enables peak energy efficiency across a wide bandwidth. Each transceiver is based on a multi-functional electromagnetic structure, which serves as a frequency doubler, sub-harmonic mixer and an on-chip radiator simultaneously. In particular, theory and design methodology of a dual-transmission-line feedback scheme are presented, which maximizes the transistor gain near its cutoff frequency $f_{\mathrm{ max}}$ and enhances the harmonic generation efficiency. The spectrometer chip has a measured total radiated power of 5.2 mW and a measured single-sideband noise figure of 14.6 ~ 19.5 dB, representing the highest generated power and sensitivity of silicon-based terahertz circuits. The chip consumes a dc power of 1.7 W. Finally, absorption spectrum of acetonitrile (CH3CN) and carbonyl sulfide is obtained, which agree with the JPL spectroscopy catalog.