26.2 A 0.08mm2 25.5-to-29.9GHz Multi-Resonant-RLCM-Tank VCO Using a Single-Turn Multi-Tap Inductor and CM-Only Capacitors Achieving 191.6dBc/Hz FoM and 130kHz 1/f3 PN Corner

VCO designs have evolved from single-resonant LC-tank VCOs to the recent multiresonant RLCM (Resistor-Inductor-Capacitor-Mutual-inductance) tank VCOs that allow reshaping of VCO phase-noise (PN) impulse sensitivity function (ISF). Two recent RF VCOs [1,2] exploited the 2
^nd
-harmonic resonance to impede the flicker-noise upconversion, achieving an FoM
_@1MHz
of up to 195.4dBc/Hz (Fig. 26.2.1). Specifically, the RLCM tank in [1] tailors a multi-turn inductor with a positive mutual coupling factor (k>0) to generate an implicit common-mode (CM) resonance at 2× the oscillation frequency (F
_OSC
). Yet, the CM resonance has a quality factor (Q) that is ~50% of its differential-mode (DM) counterpart, due to partial magnetic-flux cancellation within the multi-turn inductor. In [2], the transformer-based RLCM tank offers two intrinsically high-Q resonances at F
_OSC
and 2F
_OSC
that can effectively suppress PN in the 1/f
²
-to-1/f
³
PN regions. Still, when migrating to mm-waves both [1] and [2] face their respective challenges. A large fixed DM capacitor (C
_DM
) for fulfilling the DM-to-CM capacitance ratio of [1] largely limits the tuning range (TR) at mm-wave. For [2], its high-ratio multiturn transformer cannot maintain its Q at mm-waves.