Digital LDO Passgate Rotation for Electromigration Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digital Low Dropout (LDO) voltage regulators face reliability issues due to uneven electromigration (EM) stress across passgate transistors, leading to potential chip failures, as some passgates are used more frequently than others, resulting in higher EM stress and reduced reliability.
Innovation Solution
Implementing a digital controller that rotates active passgates during operation, varying which passgates are active and inactive at each clock cycle to distribute the load evenly among all passgates, thereby reducing average EM stress and increasing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed set of passgates is continuously activated to provide load current, then the LDO regulator can maintain stable output voltage, but the activated passgates experience uneven electromigration stress leading to reduced reliability
Solution Approach 1:
The patent implements periodic rotation of passgate activation patterns. The digital controller cycles through different combinations of passgates in a rotating sequence, ensuring each passgate experiences activation and deactivation periodically. This periodic action distributes electromigration stress evenly across all passgates over time, preventing any single passgate from bearing excessive cumulative stress and improving overall reliability.
2Reliability
If more passgates are activated to share the load, then electromigration stress per passgate is reduced, but the device area and complexity increase
Solution Approach 1:
The patent employs dynamic passgate selection where the set of activated passgates changes over time rather than remaining static. The digital controller dynamically rotates which passgates are active in each clock cycle, allowing a smaller number of passgates to share the load over time. This dynamic approach achieves stress distribution without requiring a permanently larger array of passgates, thus avoiding increased device area.
3Reliability
If passgate rotation is implemented to distribute load evenly, then electromigration stress is reduced and reliability increases, but the control complexity and switching overhead increase
Solution Approach 1:
The patent segments the passgate array into multiple groups or sets that can be independently controlled. The digital controller manages rotation through discrete segmentation of passgate activation patterns, where each segment represents a specific combination of active passgates. This segmentation approach simplifies the control logic compared to individually managing each passgate, reducing controller complexity while still achieving even stress distribution across the array.
Data Source
AI summary
A system includes a digital controller in a voltage regulator. The system also includes a passgate array including two or more passgate transistors, where the passgate array is configured to provide a load current to a load, and where the digital controller is configured to activate and deactivate each passgate transistor in the passgate array. The system also includes a feedback loop configured to provide an error signal to the digital controller, the error signal based on a difference between an output voltage of the voltage regulator and a programmed voltage for the voltage regulator. The digital controller is configured to activate or deactivate a passgate transistor based at least in part on the error signal. The digital controller is also configured to activate at least one passgate transistor and deactivate at least one passgate transistor responsive to a clock cycle.