A 0.18-μm CMOS fully integrated 0.7–6 GHz PLL-based complex dielectric spectroscopy system

A fully-integrated sensing system utilizes a ring oscillator-based phase locked loop (PLL) for wideband complex dielectric spectroscopy of materials under test (MUT). Characterization of both real and imaginary MUT permittivity is achieved with frequency-shift measurements between a sensing oscillator, with a frequency that varies with MUT-induced changes in capacitance and conductance of a delay-cell load, and an amplitude-locked loop (ALL)-controlled MUT-insensitive reference oscillator. Fabricated in 0.18-μm CMOS, the 0.7-6 GHz spectroscopy system occupies 6.25 mm2 area and achieves 3.7% maximum permittivity error.