Phase noise and amplitude issues of a wide-band VCO utilizing a switched tuning resonator

A 3.5-5.3 GHz, low phase noise CMOS VCO with switched tuning for multi-standard radios is presented in this paper. Design of low phase noise and small amplitude variations across the operating frequency is shown to be important aspects in wide-band VCO. An analytic expression for the output amplitude of the VCO is derived as a function of the switched capacitor resonator Q. The linear-time variant model was used for prediction of the phase noise and for deciding a proper tank current to achieve the minimum phase noise and amplitude variations across the frequency range. The results are verified in a fully integrated 0.18 μm VCO with measured phase noise levels of less than -115 dBc/Hz at 1 MHz offset from the carrier while dissipating 6 mW of power.