Design formula for band-switching capacitor array in wide tuning range low-phase-noise LC-VCO

A low phase noise with wide tuning range complementary LC cross-coupled voltage control oscillator (LC-VCO) using 0.18 μm CMOS technology is presented. This paper proposes a design formula for the choice of the value of varactor (ΔC_var) and band switch capacitor (C_s) for the binary-weighted band-switching LC tank which is convenient to determine the proper tuning constant for wideband, low-phase-noise operations. This general formula considers the ratio of frequency overlap (ov) and all the parasitic effects from band-switching capacitor array and transistors. The designed VCO using a 4-bit band-switching capacitor array demonstrates the operating frequencies from 4.166 to 5.537 GHz with an equivalent tuning bandwidth of 28.26%. The measured tuning range of all sub-bands is well agreed with that of the post-layout simulation results. The measured phase noise is -123.1 dBc/Hz at 1 MHz offset in the 5.2 GHz band. The calculated figure-of-merit (FoM) of this VCO was as high as -187 dB. When considering the tuning bandwidth the designed VCO obtains a FoM-bandwidth product of 52.83, which is much better than previously published works.