Wideband LC VCO with 39.3 % Frequency Tuning Range for Dielectric Spectroscopy System

Abstract

To detect the permittivity of various materials, an accurate reference frequency over wideband is required. In this work, we propose a LC voltage controlled oscillator (VCO) suitable for a dielectric spectroscopy system covering C-band frequency range. Wide tuning range of a LC VCO is achieved by a 3-bit controlled capacitor bank and a NMOS varactor. Coarse frequency tune is provided by the capacitor bank with 100fF resolution and its capacitance covers up to 700fF. NMOS varactor provides the fine tune covering 50fF to 200fF capacitance ranges. The prototype circuit is implemented in 28-nm CMOS technology with the active area of 0.33 mm × 0.53 mm, while consuming 4.35 mW power consumption from a 1.1 V supply voltage. The proposed VCO operates from 4.5 to 6.7 GHz (39.3% tuning range) and achieves a low phase noise of-105.9 dBc/Hz at 1 MHz offset frequency.