Influence of Temperature on the EFT Immunity of Multistage Integrated Oscillators

The reliable operation of an integrated circuit (IC) can be affected by transient electromagnetic disturbances and temperature variations. In this paper, the performance of three oscillator circuits, namely 3- and 5-stage current-starved voltage controlled oscillators and a 3-stage ring oscillator, is compared with respect to electrical fast transients (EFT) under the influence of thermal stress. The main objective is to compare and assess, by means of measurements, the EFT immunities of integrated oscillators with the same electrostatic discharge (ESD) protections but different circuit topologies. The failure modes caused by EFT are proposed based on the considered failure criterion. Moreover, the importance of the IC package on the immunity levels of each oscillator is investigated. The output frequency response of each oscillator to the combined EFT and temperature stresses is analyzed without the external parasitics. The results show that the 5-stage CSVCO is most resilient towards temperature variations, whereas it is the least immune to the combined effect of EFT and temperature. Moreover, a distinct behavior in each tested oscillator's frequency is observed for the in-phase EFT injections due to the topology of the circuit. Relevant MOSFET characteristics such as on-state drain-to-source resistance, power dissipation, effective mobility and threshold voltage are further analyzed under the influence of thermal stress and EFT. The root cause of higher EFT susceptibility of the 5-stage CSVCO is found to be the considerable variation of the on-state resistance due to the combined reduction of effective mobility and absolute threshold voltage levels of the MOSFETs.