Variable-Width Power Gating for Low-Noise Rail Wake-Up
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Solution Overview
Problem
Conventional power gating modules in integrated circuit devices have a fixed effective width, leading to large instantaneous current draw and noise, which can cause electromigration violations and make it difficult to determine if the module is oversized or undersized, affecting performance characteristics.
Innovation Solution
A variable-width power gating module that modulates the effective width by enabling only a subset of transistors, allowing for different combinations to optimize performance parameters such as maximum frequency and minimum voltage, and includes control logic for gradual wake-up and wake-down transitions to manage transient current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional fixed-width power gating module is used, then the current carrying capacity is sufficient to power the secondary rail, but large instantaneous current draw and noise occur, causing electromigration violations
Solution Approach 1:
The power gating module divides the transistor array into multiple independently controllable groups (first subset and second subset). This segmentation allows selective activation of transistors based on actual power requirements, enabling gradual current transitions that reduce instantaneous current draw and associated noise while maintaining sufficient current carrying capacity when needed.
Solution Approach 2:
The power gating module transitions from a fixed-width configuration to a dynamic variable-width configuration. The effective width is adjusted by selectively enabling different subsets of transistors based on operational requirements. This dynamic adjustment allows the module to optimize between current carrying capacity and noise reduction, preventing electromigration violations while maintaining reliability.
2Power
If all transistors are enabled simultaneously to provide sufficient current, then the secondary rail is properly powered, but the instantaneous current draw increases causing voltage fluctuations and IR drops
Solution Approach 1:
The control logic enables transistors in a predetermined sequence through cascaded enable signals. Before the full current load is applied, a first subset of transistors is enabled to gradually charge the secondary rail. This preliminary action allows the rail voltage to stabilize before additional transistors are activated, preventing voltage fluctuations and IR drops that would occur with simultaneous activation.
Solution Approach 2:
The power gating module employs periodic or staged activation of transistor subsets rather than simultaneous activation. The cascaded enable signals create a time-separated activation pattern where different groups of transistors are enabled at different times. This periodic action distributes the current draw over time, reducing instantaneous peaks and associated voltage fluctuations.
3Power
If the power gating module width is increased to ensure adequate current supply, then the secondary rail can be powered, but it becomes difficult to determine if the module is oversized or undersized, affecting performance characteristics
Solution Approach 1:
The power gating module employs variable-width control where the effective transistor width is dynamically adjusted by selectively enabling different subsets. This allows the module to adapt its current carrying capacity to match actual operational requirements, eliminating the need to oversize the module while maintaining adequate current supply. The performance can be optimized by configuring the control logic to enable appropriate subsets based on specific operational conditions.
Solution Approach 2:
The invention changes the effective width parameter of the power gating module by selectively activating different transistor subsets. Instead of using a fixed width that must accommodate worst-case scenarios, the effective width parameter is variable and can be adjusted to match actual power requirements. This parameter change enables both adequate current supply and performance optimization.
4Use of energy by moving object
If multiple voltage rails are used to create voltage islands for selective power control, then power consumption is reduced, but the device complexity increases
Solution Approach 1:
The power gating module segments the transistor population into multiple independently controllable subsets, each manageable by dedicated control logic. This segmentation allows selective power control of different portions of the circuit without requiring complex global management of multiple voltage rails. The modular structure simplifies the control architecture while maintaining the power savings benefits of selective power gating.
Data Source
AI summary
A semiconductor device includes a primary voltage rail, a secondary voltage rail, a plurality of transistors coupled between the primary and secondary voltage rails, and control logic operable to enable a first subset of the plurality of transistors to couple the primary voltage rail to the secondary voltage rail. During a steady state condition, the first subset comprises less than all of the plurality of transistors.