Implementation of the ultra-low power load-independent LC VCO

In this paper the influence of the external load on the key parameters of the commonly used cross-coupled LC VCO architecture is investigated. It is shown, that even high ohmic external load decreases the impedance of the resonator, limits the frequency tuning range, degraded the phase noise and increases the power dissipation of the structure. Additionally, based on the carried out analyses, the novel load-independent LC VCO architecture is implemented and characterized. In the presented VCO topology, the resonator is isolated from the external load, by connecting the VCO outputs in the common collector configuration. As a result, the oscillator with the power consumption of 540 μW from the 1.8 supply voltage is achieved. The measured frequency tuning range of the VCO lies between 6.30 GHz and 8.59 GHz and the phase noise is better than -100 dBc/MHz at the frequency offset of 1 MHz within entire tuning range.