Comparison of microstrip stub resonators for dielectric sensing in low-power K-band VCO

This paper presents the design and comparison of three K-band sensing oscillators in standard 0.25 μm SiGe:C BiCMOS technology with featuring an open-stub, shunt-stub and a combination of both. The different stub types are combined with the inductive and capacitive elements of the particular oscillator and serve as the sensing elements in the respective setup. The input impedances of the stubs highly depend on the permittivity of the medium. Therefore, the oscillation frequencies correspond to the dielectric material under test (MUT). The sensors response to different dielectric properties has been investigated using different Methanol-Ethanol solutions The conducted experiments show that the proposed architectures indicate the MUTs permittivity with a maximum frequency shift of 4.3 % for a change in permittivity of 2.4. Each of three sensors has an chip-area of 0.6 mm2 and consumes less than 12 mW power. The proposed sensor is a potential component for future low-power front-ends to perform minimally invasive investigations of bio-materials.