2.5 A complementary VCO for IoE that achieves a 195dBc/Hz FOM and flicker noise corner of 200kHz

An LC oscillator can achieve near optimal performance if the common-mode of the circuit is designed to resonate at twice the oscillation frequency [1-3]. Common-mode resonance can be accomplished with an explicit tail inductor [1] or implicitly by designing the primary resonant tank such that the differential mode is half the common-mode [2,3]. Figures 2.5.1a and 2.5.1b show the NMOS-only and complementary versions [4] of Hegazi's explicit common mode resonance topology, while Fig. 2.5.1c shows a design that employs implicit common-mode resonance. Implicit common-mode resonance has the advantage of a more easily controlled and modelled common-mode and requires one less inductor, but so far has only been applied to NMOS-only oscillators [2,3]. The primary advantage of an NMOS-only design is that, for a given inductance, lower absolute phase noise can be achieved owing to the larger maximum output swing; however, a complementary design is more suitable for low-power applications with more modest phase-noise specifications (such as IoE) where phase noise per unit current and area is important. With an eye to such applications, this paper extends the concept of implicit common-mode resonance to an ultralow power complementary design (i.e. the missing topology in Fig. 2.5.1d).