An RF MEMS Sensor Driver/Readout SoC With Resonant Frequency Shift and Closed-Loop Envelope Regulation for Portable Microplastic Detection

This article proposes a low-cost and portable device that enables automated detection of microplastic (MP) by using a high-precision 1.1-1.15-GHz radio frequency (RF) micro-electro-mechanical system (MEMS) sensor driver/readout system-on-chip (SoC). The proposed driver and readout SoC operate as an RF signal generator and a spectrum analyzer, respectively, enabling the analysis of resonant frequency shifts corresponding to MP concentration. The driver SoC uses closed-loop power amplifier (PA) envelope regulation (CPA-ER) to maintain consistent output power against frequency shifts. The driver SoC exhibits an output power up to 0.23 dBm at 1.14 GHz and achieves a small output power variation of less than 4.9% between 1.1 and 1.15 GHz. The proposed readout SoC can detect a minimum input power of $-$ 10 dBm while achieving a dynamic range (DR) of 18 dB and a low linearity error of 1%. The 180-nm CMOS driver SoC and 250-nm CMOS readout SoC occupy a silicon area of 7.1 and 3.8 mm $^{2}$ , respectively. Upon injecting 5 $\mu $ L of 1% regular standard polyethylene (PE) dispersion into the RF MEMS sensor five times, the resonant frequency shifts up to 10 MHz. Also, when 5 $\mu $ L of 1% amorphous polypropylene (PP) dispersion is injected 16 times, the resonant frequency shifts by 14 MHz, verifying that the proposed system can detect MP consisting of PE and PP.