Comprehensive Analytical Comparison of Ring Oscillators in FDSOI Technology: Current Starving Versus Back-Bias Control

Schramme, Maxime [UCL] Van Brandt, Léopold [UCL] Flandre, Denis [UCL] Bol, David [UCL]

Back-bias control is a new degree of freedom brought by fully-depleted silicon-on-insulator (FDSOI) CMOS technologies, which can be used to control the oscillation frequency of voltage-controlled ring oscillators (VCROs). The resulting VCRO architecture is called a back-bias-controlled oscillator (BBCO). This paper compares it with the conven- tional current-starved ring oscillator (CSRO) topology in terms of power consumption and phase noise figure-of-merit (FoM), while taking practical design constraints of process-voltage- temperature (PVT) robustness and frequency tuning range into account. The proposed comprehensive analysis takes advantage of relevant and compact analytical models, as well as extensive pre-layout simulation results. The comparison is made at four different target oscillation frequencies, which are representative of frequency synthesis for WiFi/Bluetooth/LPWAN wireless com- munications and of clock generation for smartphone/Internet-of- Things processors: 300 MHz, 868 MHz, 2.45 GHz, and 5.18 GHz. In 28-nm FDSOI technology, the results demonstrate that BBCOs can intrinsically reach 1.69 to 4.63× lower minimum power consumption and slightly better FoM values than CSROs