A 3–10-GHz CMOS Time-Domain Complex Dielectric Spectroscopy System Using a Contactless Sensor

Abstract

This article presents an integrated time-domain (TD) microwave broadband dielectric spectroscopy (MBDS) system in the 3–10-GHz frequency span divided into nine subbands. The generated multitone input pulse with 1-GHz bandwidth is upconverted to RF frequencies in the transmitter using a broadband single-sideband (SSB) mixer to suppress the lower sideband of the excited signal and prevent the signal distortion at the configured dc-free direct conversion receiver with the center frequency of 500 MHz at the baseband. The upconverted pulse is passed through a contactless sensor in TD where the material under test (MUT) is placed in the middle of the two ultra-wideband (UWB) Vivaldi antennas coupled in their radiative near field. To identify both the real ( $\epsilon _{r}'$ ) and imaginary ( $\epsilon _{r}''$ ) parts of the MUT’s permittivity, the impact of the entire system on MUT characterization is alleviated by designing the system subblocks and the sensor with flat gain and constant group delay over the entire frequency range. The proposed MBDS system is fabricated in 65-nm CMOS and occupies an active area of 1.24 mm2 while consuming 64~69 mW from a 1-V supply. As a proof of concept, the complex dielectric permittivity of different pure organic chemical liquids has been detected within the desired frequency range with a customized quartz-glass cuvette with the MUT volume of ~ 5 mL by calibrating the sensor using the variations in the phase and the magnitude after FFT with respect to the reference material (air). The system results in an rms error of less than 0.2% and 0.4% for $\epsilon _{r}'$ and $\epsilon _{r}''$ , respectively, compared with theory. To the best of our knowledge, this is the first CMOS TD MBDS system with a homodyne RF transceiver architecture including an on-chip UWB excitation pulse generation and the contactless sensor.