A CMOS Microwave Broadband Adaptive Dual-Comb Dielectric Spectroscopy System for Liquid Chemical Detection
An integrated ultra-wideband (UWB) microwave coherent dual-comb spectroscopy (DCS) system, with two on-chip frequency combs with a tunable and slightly different repetition frequency rates, is presented for liquid chemicals detection. One of the frequency combs interrogates a coplanar waveguide (CPW) planar transmission line sensor loaded with the material under test (MUT) while the other identical empty sensor is excited by the second comb. Two frequency combs are then heterodyned using a UWB mixer to generate the dual-comb output that represents the properties of the MUT from microwave frequencies mapped to low-frequencies eliminating the need to use high-frequency analog-to-digital converters (ADCs). To achieve detection of both real and imaginary parts of the complex permittivity of liquid samples, an adaptive sampling method along with phase-locking of all sources are utilized. The 3–10 GHz microwave DCS system fabricated in 65 nm CMOS, occupies 1.98 mm² an area and consumes ~72 mW from a 1 V supply. To verify the chemical detection, MUTs including methanol, ethanol and water results at the output of DCS system in this paper are presented.