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Ring oscillators provide a versatile and area-efficient means of on-chip frequency generation in modern CMOS processes. This paper presents an in-depth analysis and benchmarking of three ring oscillator architectures implemented in a 45-nm CMOS technology: conventional CMOS, NMOS-only, and current-starved tunable designs. Circuit operation, noise analysis, layout considerations, and tuning techniques are detailed. Post-layout simulations demonstrate phase noise as low as −110 dBc/Hz with power consumption down to 2.4 mW. A figure-of-merit (FOM) evaluation indicates that the NMOS-only cross-coupled variant, with its lower component count, achieves the best balance of phase noise, power, and tuning range. Overall trends reveal design techniques to optimize ring oscillator performance for a given target frequency and CMOS process node.