Power-Gate Charge Recycling for Short Idle Periods
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Solution Overview
Problem
Conventional power-gating techniques face inefficiencies due to the large size of power-gate transistors, which consume more energy when switching on and off, especially during short idle periods, leading to reduced usage and increased energy consumption.
Innovation Solution
A power-gate circuit with a power-gate transistor that recycles charge by routing it from the gate terminal to the rail during idle mode and back during active mode, using a switch to control the flow, allowing the transistor to remain active even during short idle periods, thus minimizing energy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power-gate transistor is turned OFF during idle mode to reduce leakage current, then power consumption is reduced, but energy is consumed for switching the transistor ON and OFF
Solution Approach 1:
The patent recovers the charge that would otherwise be discarded when turning off the power-gate transistor. A recovery circuit captures the charge from the gate terminal during the OFF transition and stores it for reuse, thereby reducing the energy penalty associated with repeated switching operations while maintaining leakage current reduction benefits
2Loss of energy
If the power-gate transistor is made large in size to handle power gating, then leakage current reduction is improved, but switching energy consumption increases
Solution Approach 1:
The recovery circuit captures and stores the charge that would be lost during transistor switching, enabling the use of larger power-gate transistors for better leakage control without proportionally increasing switching energy consumption, as the recovered charge offsets the switching energy penalty
3Adaptability or versatility
If the power-gate transistor is switched frequently for short idle periods, then power gating control is improved, but efficiency decreases due to high switching energy relative to leakage savings
Solution Approach 1:
The charge recovery circuit makes frequent switching viable by capturing and reusing the charge that would otherwise be wasted, thereby improving switching efficiency and enabling adaptable power gating control even during short idle periods where the leakage savings exceed the recovered switching energy cost
Data Source
AI summary
A power-gate circuit includes a power-gate transistor operable to switch to decouple a first supply voltage from a second supply voltage during an idle mode, and to couple the first supply voltage to the second supply voltage during a full operational mode. Part of the charge stored at a gate terminal of the power-gate transistor, would have been otherwise flushed to ground while turning on the power-gate transistor, is routed to the rail of the second supply voltage of the logic block. Part of the charge on the rail of the second supply voltage is used to charge the gate terminal of the power-gate transistor to deactivate the power-gate transistor if the logic block goes to the idle mode. Energy is saved both ways because of the charge recycling and the ability to use the power-gate circuit even in cases where the duration of the idle mode may be short.