20.1 A 5.0-to-6.36GHz Wideband-Harmonic-Shaping VCO Achieving 196.9dBc/Hz Peak FoM and 90-to-180kHz 1/f3 PN Corner Without Harmonic Tuning

Since 2001 [1], LC VCOs have been demonstrating significant improvements of figureof-merit (FoM) and 1/f ³ phase noise (PN) corner [2-5] by exploring common-mode (CM) resonance at twice the oscillation frequency (2F _OSC ). In addition, for area reduction, the shaping of the impulse sensitivity function (ISF) has evolved from explicit with two coils [1] to implicit with one coil [2]. Yet, as depicted in Fig. 20.1.1, the latter suffers from large CM magnetic-flux cancellation, resulting in a much lower CM impedance |Z _CM | that is -0.64 of its differential-mode (DM) impedance |Z _DM |. The VCO in [3] achieves a high FoM@10MHz up to 191.4dBc/Hz by boosting |Z _CM | at 2F _OSC and |Z _DM | at 3F _OSC . Yet, to uphold an optimal performance over the tuning range (TR), the VCO in [3]still requires manual harmonic tuning for aligning the 1 ^st -to-2 ^nd and 1 ^st -to-3 ^rd harmonic resonances. This denotes a narrowband effect. For the VCO in [4], which features a four-winding transformer with no harmonic tuning, there is a large variation of FoM _@10MHz (190.7 to 196.5dBc/Hz) and 1/f ³ PN corner (60 to 600kHz) across the TR.