Current-Starved Inverter Cell Design Trade-Offs for Single Capacitively Coupled Ring VCOs

This paper presents a comparative study of inverter cell topologies for use in a single capacitively coupled (SCC) ring VCO targeting multi-phase RF applications. Three inverter cells are investigated: nMOS-only (N), pMOS-only (P), and complementary nMOS-pMOS (NP), each implemented with current-starved control for frequency tuning. The cells are designed in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$28-\text{nm}$</tex> FD-SOI technology under a common parameterization, ensuring that performance differences arise from intrinsic architectural properties rather than transistor sizing. Simulation results compare frequency tuning range, power consumption, output swing, signal symmetry and phase noise. The N cell achieves the widest tuning range, the NP cell offers better symmetry and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{P}$</tex> cell shows limited swing and higher asymmetry but with lower power consumption. These results reveal intrinsic trade-offs between efficiency, signal integrity, and spectral purity, providing practical guidelines for inverter selection in SCC VCO designs.