Current-Mode Dielectric Spectroscopy for Liquid Permittivity Measurement

In this work, we propose a current-mode dielectric spectroscopy integrated circuit (IC) for the detection of liquids permittivity at microwave frequency range. The current-mode sensing scheme presents wideband operation with enhanced dynamic range compared to conventional voltage-mode sensing approach. A low intermediate frequency (IF) receiver architecture further provides better performances in flicker noise, dc offset, and harmonic mixing that degrade a sensor accuracy in zero-IF receiver architecture. Measured maximum conversion gain is 31.4 dB at 0.4 GHz RF frequency, while the 1dB-compression point (P_1dB) is measured to be -8 dBm at 1 GHz RF frequency. The operation frequency of the proposed spectroscopy IC is from 50 MHz to 4 GHz according to 3 dB bandwidth. The permittivity measurements for propanol across the frequency range of 0.03-10 GHz are performed with root mean square (rms) permittivity error of 0.49. The dielectric spectroscopy IC is fabricated in 28-nm CMOS technology with active area of 0.5 mm × 0.2 mm only, while consuming 13 mW from a 1.2 V supply.