A CMOS Fractional- $N$ PLL-Based Microwave Chemical Sensor With 1.5% Permittivity Accuracy

A highly sensitive CMOS-based sensing system is proposed for permittivity detection and mixture characterization of organic chemicals at microwave frequencies. The system determines permittivity by measuring the frequency difference between two voltage-controlled oscillators (VCOs); a sensor oscillator with an operating frequency that shifts with the change in tank capacitance due to exposure to t...