CMOS cross-coupled VCO architecture comparison at 2GHz and 16GHz

This paper presents a comparison study between double-switch (DS) and single-switch (SS) cross-coupled CMOS VCO architectures at 2 GHz and 16 GHz. The oscillators are designed with optimal differential tank oscillation amplitude, which is equal to the threshold voltage of the cross-coupled transistors. Measurement data from prototype oscillators show that the DS architecture can achieve a better performance than the SS architecture at low oscillation frequencies. However, as frequency increases the single-switch architecture outperforms the double-switch counterpart. By employing the single-switch cross-coupled architecture with an optimal oscillation amplitude, a high performance 23.5 GHz VCO is designed and demonstrated with an FOM of 184 dB, which is the best compared to any reported Si-based VCO in the 20 GHz - 30 GHz frequency range.