A 1.5 GHz-1.8 GHz Voltage Controlled Oscillator for Passive LC Sensors Readout

In this paper a voltage-dip based readout interface of passive LC sensors is presented. Our work includes improvements of the original parallel tuned Colpitts voltage-controlled oscillator (VCO) topology to meet requirements for an interface with passive LC sensors in GHz-range. Our redesign provides stable amplitude of output oscillations independent of the input tune voltage, multichannel operation, and linear range of output frequency (1.5 GHz-1.8 GHz) versus input tune voltage (0 V-15 V). The proposed VCO was implemented as a part of the voltage-dip based readout interface of resonant frequency estimation of passive LC sensors. Conducted analysis showed that the presented readout topology could operate with coupling factors greater than 0.05, and that readout is independent to changes of coupling factor. Additional tests revealed that the proposed topology is sensitive to changes of the resonant frequency greater than 0.187%.