Reliability Enhanced Digital Low-Dropout Regulator with Improved Transient Performance

Overview & Synopsis

Digital low-dropout voltage regulators (DLDOs) have drawn increasing attention for the easy implementation within nanoscale devices. Despite their various benefits over analog LDOs, disadvantages may arise in the form of bias temperature instability (BTI) induced performance degradation. In this Chapter, conventional DLDO operation and BTI effects are explained. Reliability enhanced DLDO topologies with performance improvement for both steady-state and transient operations are discussed. DLDOs with adaptive gain scaling (AGS) technique, where the number of power transistors that are turned on/off per clock cycle changes dynamically according to load current conditions, have not been explored in view of reliability concerns. As the benefits of AGS technique can be promising regarding DLDO transient performance improvement, a simple and effective reliability aware AGS technique with a steady-state capture feature is proposed in this work. AGS senses the steady-state output of a DLDO and reduces the gain to the minimum value to obtain a stable output voltage. Moreover, a novel unidirectional barrel shifter is proposed to reduce the aging effect of the DLDO. This unidirectional barrel shifter evenly distributes the load among DLDO output stages to obtain a longer lifetime. The benefits of the proposed techniques are explored and highlighted through extensive simulations. The proposed techniques also have negligible power and area overhead. NBTI-aware design with AGS can reduce the transient response time by 59.5% as compared to aging unaware conventional DLDO and mitigate the aging effect by up to 33%.