SRAM Retention Voltage Regulator Tracking Leakage Current
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Solution Overview
Problem
In power-efficient silicon memories, it is challenging to track and maintain the retention voltage of static random-access memory (SRAM) in retention mode, as it varies with temperature and process variations, leading to increased power consumption when overcompensating for worst-case scenarios.
Innovation Solution
A circuit is implemented to track the leakage current and threshold voltage of SRAM bitcells, using a voltage regulator to supply a supply voltage proportional to the tracked threshold voltage, thereby reducing power consumption by avoiding overcompensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a supply voltage is set based on worst-case operating conditions assumption, then the SRAM cells will reliably retain data, but power consumption increases
Solution Approach 1:
The voltage regulator dynamically adjusts the supply voltage based on real-time feedback from leakage current sensing and threshold voltage tracking circuits, transitioning from a static worst-case voltage to an adaptive voltage that matches actual operating conditions
Solution Approach 2:
The system implements feedback mechanisms where leakage current is sensed and threshold voltage is tracked, feeding this information back to the voltage regulator to continuously adjust the supply voltage and maintain it at the minimum required level for data retention
2Use of energy by moving object
If the supply voltage is reduced to minimize standby power, then power consumption decreases, but the SRAM cells may fail to retain data
Solution Approach 1:
The patent replaces simple mechanical voltage reduction with an intelligent control system that uses leakage current sensing, threshold voltage tracking, and feedback control to precisely maintain voltage at the retention threshold
Solution Approach 2:
The system changes the voltage parameter dynamically based on tracked threshold voltage and leakage current, adjusting the supply voltage to match the actual retention requirements rather than using a fixed conservative value
3Use of energy by moving object
If the retention voltage is tracked accurately across temperature and process variations, then power consumption is minimized, but the circuit complexity increases
Solution Approach 1:
The patent uses copying by creating mirror circuits that replicate the SRAM bitcell structure to sense and track threshold voltage and leakage current characteristics without requiring direct measurement of the actual storage cells
Solution Approach 2:
The voltage regulator circuit performs multiple functions including leakage current sensing, threshold voltage tracking, feedback control, and voltage adjustment, consolidating these functions into an integrated system rather than separate circuits
Data Source
AI summary
Systems, apparatuses, and methods for tracking a retention voltage are disclosed. In one embodiment, a circuit is utilized for generating a standby voltage for a static random-access memory (SRAM) array. The circuit tracks the leakage current of the bitcells of the SRAM array as the leakage current varies over temperature. The circuit mirrors this leakage current and tracks the higher threshold voltage of a p-channel transistor or an n-channel transistor, with the p-channel and n-channel transistors matching the transistors in the bitcells of the SRAM array. The circuit includes a voltage regulator to supply power to the SRAM array at a supply voltage proportional to the higher threshold voltage tracked. Setting a supply voltage of the SRAM array based on threshold voltages and leakage current may reduce power consumption as compared to using a supply voltage based on a worst case operating conditions assumption for the SRAM array.