SRAM Charge Recycling Circuit for Power Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power consumption in memory devices, such as SRAM, increases due to leakage current, especially in high-performance embedded memory where charge recycling during transitions from active to standby mode is inefficient, leading to wasted power as most charge is dumped into ground.
Innovation Solution
A memory device with multiple banks, including a block of SRAM that transitions between active and standby modes, utilizes a recycling circuit to transfer charge from one SRAM block to others when entering standby mode, using a regulator circuit to manage voltages and selectively open switches to optimize charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If charge recycling is implemented in traditional SRAM cells, then power consumption is reduced, but the bit-line discharge is relatively small compared to total charge, so most charge is still dumped into ground
Solution Approach 1:
The memory device is divided into multiple banks with independent charge recycling paths. Each bank can recycle charge independently to other banks through dedicated recycling circuits, separating the charge recycling function from the traditional bit-line based approach. This segmentation allows much larger portions of charge to be recycled rather than dumped to ground.
Solution Approach 2:
A recycling circuit acts as an intermediary between the SRAM cell capacitance and the power supply/ground. Instead of directly discharging charge to ground or recycling it through the bit-line, the recycling circuit mediates the charge transfer process, enabling efficient charge redistribution to other banks that are in precharge state.
2Quantity of substance
If more SRAM cells are connected to each bit line to increase capacity, then storage capacity increases, but more charge is needed to increase SRAM-cell voltage during read-assist operation, increasing power consumption
Solution Approach 1:
The memory is organized into multiple banks that are independently controllable and can be independently charged. This segmentation allows the system to serve multiple banks simultaneously, reducing the charge requirement per bank while maintaining overall capacity. Each bank operates with its own charge recycling path, eliminating the need to service all banks through a single bit-line.
Solution Approach 2:
Banks that are not currently in use are placed in standby mode with their charge recycling circuits pre-configured. When a bank needs to be accessed, it can be quickly brought to active state by recycling charge from other banks that are in precharge state, eliminating the need to charge all banks fully before each operation.
3Reliability
If read assist voltage control is used to reduce leakage current, then leakage current is reduced, but power is wasted because large capacitance is charged up to high voltage and subsequently dumped into low voltage during precharge cycle
Solution Approach 1:
Instead of discarding the charge stored in SRAM cell capacitance during the precharge cycle (where it is dumped to ground), the recycling circuit recovers this charge and redirects it to other banks that need charging. This recovers the energy that would otherwise be wasted, reducing the total power consumption while maintaining the leakage current reduction benefits of read assist.
Solution Approach 2:
The charge that would normally be considered waste product during precharge is converted into a useful resource. The recycling circuit takes the charge that would be discarded and uses it to charge other banks, transforming the harmful energy loss into a beneficial charging action that reduces overall power consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces power consumption and improves performance by recycling charge stored during active mode for use in precharge cycles, thereby minimizing waste and enhancing operational efficiency.
Implementation Method 1
a recycling circuit that selectively opens a second switch between the first switch and the first power-signal line when the block of SRAM transitions from the active operating mode to the standby mode, thereby transferring charge from the block of SRAM to the one or more additional blocks of SRAM in the one or more additional banks
Data Source
AI summary
A memory device that includes multiple blocks of static random access memory (SRAM), which each have a standby mode and an active operating mode, is described. During the active operating mode, a selection circuit couples a higher voltage from a first power-signal line and a power-supply circuit to a given block of SRAM, and during the standby mode the selection circuit couples a lower voltage from a second power-signal line to the given block of SRAM. Note that a regulator circuit regulates the lower voltage on the second power-signal line by selectively opening or closing a first switch between the first power-signal line and the second power-signal line. Furthermore, a recycling circuit selectively opens a second switch between the first switch and the first power-signal line when the block of SRAM transitions from the active operating mode to the standby mode, thereby transferring charge from the block of SRAM to other blocks of SRAM.