Phase displacement study in MOSFET based ring VCOs due to heavy-ion irradiation using 3D-TCAD and circuit simulation

This paper analyzes the radiation tolerance of both single ended and differential ring VCO in the presence of SET in 90 nm CMOS process technology. Phase displacement is an important metric in assessing the susceptibility and suitability of any frequency synthesizer in the presence of SET. Through device level characterization using Synopsys TCAD and extensive circuit level simulation and verification, for heavy ion dosage with LET between 20 ((MeV-cm2)/mg) and 200 ((MeV-cm2)/mg), the current starved differential delay cell based 3-stage differential ring VCO exhibits a phase displacement improvement of around 20% compared to a current starved inverter based single ended ring VCO oscillating at 420 MHz. When the number of stages in differential ring VCO are increased from 3 to 7 the phase displacement is reduced by a factor of 57%. However, to achieve similar phase displacement improvement in inverter based single ended ring VCO required in excess of 15 stages. The active area for the differential ring VCO decreases by almost 40% as the number of stages increases.