Shift-Register DLDO Control for NBTI Aging Mitigation
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Solution Overview
Problem
Digital low-dropout voltage regulators (DLDOs) face significant performance degradation due to negative bias temperature instability (NBTI), which affects maximum output current capability, load response time, and voltage droop, especially under varying load current and temperature conditions, leading to reliability concerns in critical applications like microprocessors.
Innovation Solution
Aging-aware DLDOs employ a unidirectional shift register to evenly distribute electrical stress among power transistors, mitigating NBTI-induced degradation by activating and deactivating transistors in a manner that balances stress across all transistors under arbitrary load conditions, thereby enhancing reliability without significant power or area overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DLDO designs are used, then the device structure is simple and easy to manufacture, but NBTI induces significant performance degradation in maximum output current capability, load response time, and voltage droop
Solution Approach 1:
The patent divides the single power transistor into multiple parallel power transistors (e.g., 4 transistors) and uses a shift register to sequentially activate them. This segmentation allows the electrical stress to be distributed across multiple devices, reducing NBTI degradation on each individual transistor while maintaining the required output current capability.
Solution Approach 2:
The patent implements periodic activation of power transistors using a shift register controlled by a clock signal. Each transistor is activated for a specific duration and then deactivated, allowing it to recover from electrical stress. This periodic action reduces cumulative NBTI degradation while maintaining continuous power delivery capability.
2Reliability
If multiple power transistors are used to share electrical stress, then NBTI degradation is reduced, but the device area and control circuit complexity increase
Solution Approach 1:
The patent combines multiple power transistors in parallel configuration, where each transistor can independently contribute to the total output current. The shift register control circuit manages their activation sequences, allowing stress distribution across multiple devices while maintaining compact integration.
Solution Approach 2:
The patent introduces dynamic control through a shift register that sequentially activates power transistors based on clock cycles. This dynamic activation pattern allows the system to adaptively distribute stress over time, reducing NBTI degradation without requiring all transistors to be simultaneously active, thereby optimizing area utilization.
3Productivity
If power transistors are continuously activated to maintain output current capability, then the current delivery is maintained, but NBTI-induced performance degradation accelerates
Solution Approach 1:
The patent employs periodic activation of power transistors using a shift register controlled by a clock signal. Each transistor is activated for a specific duration and then deactivated, allowing it to recover from electrical stress. This periodic action reduces cumulative NBTI degradation while maintaining continuous power delivery capability.
Solution Approach 2:
The patent implements a recovery mechanism where power transistors are periodically deactivated to allow stress relief and performance recovery. The shift register control ensures that while one transistor is active and delivering current, others are in recovery mode, reducing cumulative NBTI degradation and extending device lifetime.
Data Source
AI summary
An apparatus and method are provided for mitigating performance degradation in digital low-dropout voltage regulators (DLDOs) caused by the effects of aging on the power transistors of the DLDO, such as by the effects of negative bias temperature instability (NBTI)-induced aging, for example. The apparatus comprises a shift register for use in a DLDO that is configured to activate and deactivate power transistors of the DLDO to evenly distribute electrical stress among the transistors in a way that mitigates performance degradation of the DLDO under various load current conditions. In addition, the shift register and methodology can be implemented in such a way that nearly no extra power and area overhead are consumed.