Adaptive Bias Scheme for Non-Volatile Resistive Crossbar Arrays
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Solution Overview
Problem
Resistive memory crossbar arrays face significant energy consumption challenges during write operations, particularly due to the dependence on device and circuit characteristics and bias schemes, with existing bias schemes like V/2 and V/3 not clearly demonstrating energy efficiency advantages, and the energy consumption increasing with array size and number of selected cells.
Innovation Solution
An adaptive and dynamic bias scheme is implemented, where a read-before-write operation determines the number of cells to be written, comparing it to a threshold value to switch between V/2 and V/3 bias schemes, using tunable voltage regulators to optimize energy efficiency based on array size and non-linearity factor, thereby reducing write energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed bias scheme (V/2 or V/3) is used for write operations, then the circuit design is simple, but energy consumption increases with array size and number of selected cells
Solution Approach 1:
The patent implements a dynamic bias scheme that switches between V/2 and V/3 biasing modes based on the number of selected cells. When the number of selected cells is small, V/2 bias is used; when it exceeds a threshold, V/3 bias is applied. This dynamic adaptation resolves the contradiction by making the bias scheme flexible rather than fixed, reducing energy consumption for large arrays while maintaining simplicity for small arrays.
Solution Approach 2:
The patent changes the bias voltage parameter dynamically based on operating conditions. By adjusting the bias voltage from V/2 to V/3 depending on the number of selected cells, the system optimizes energy consumption across different array sizes and selection scenarios, resolving the contradiction between fixed design simplicity and variable energy efficiency.
2Speed
If the bias voltage is increased to improve write speed, then write operation speed improves, but energy consumption increases
Solution Approach 1:
The patent dynamically adjusts the bias voltage level based on the number of selected cells. For small numbers of selected cells, V/2 bias provides sufficient write speed with lower energy. For larger numbers, V/3 bias is applied to maintain write speed while optimizing overall energy consumption. This dynamic approach resolves the contradiction by matching bias voltage to actual operational needs.
Solution Approach 2:
The patent applies partial biasing (V/3) only when necessary (when number of selected cells exceeds threshold), rather than always using the higher V/2 bias. This partial application of higher voltage resolves the contradiction by providing sufficient write speed only when needed, reducing unnecessary energy consumption during operations with fewer selected cells.
3Device complexity
If a single bias scheme is used for all array sizes, then the control logic is simple, but energy efficiency decreases for larger arrays
Solution Approach 1:
The patent implements a dynamic control logic that selects between V/2 and V/3 bias schemes based on a simple threshold comparison of the number of selected cells. This resolves the contradiction by introducing minimal complexity (a threshold check) that yields significant energy efficiency improvements for larger arrays, rather than using a single suboptimal bias scheme for all cases.
Solution Approach 2:
The patent changes the bias scheme parameter based on array size and number of selected cells. By implementing a threshold-based parameter change from V/2 to V/3 bias, the system achieves better energy efficiency for larger arrays while maintaining relatively simple control logic, resolving the contradiction between control simplicity and energy efficiency.
4Speed
If V/2 bias scheme is used, then write speed is maintained, but leakage current increases for large arrays
Solution Approach 1:
The patent dynamically switches from V/2 to V/3 bias scheme when the number of selected cells exceeds a threshold. This resolves the contradiction by using V/2 bias (which maintains write speed) only when necessary (small number of selected cells), and switching to V/3 bias (which reduces leakage current) when the array size and number of selected cells make leakage significant.
Solution Approach 2:
The patent changes the bias voltage parameter from V/2 to V/3 based on the number of selected cells. This parameter change resolves the contradiction by reducing leakage current through lower bias voltage (V/3) when array size makes leakage significant, while maintaining V/2 bias (which provides better write speed) when the number of selected cells is small.
Data Source
AI summary
A method to adaptively and dynamically set a bias scheme of a crossbar array for a write operation includes: performing a read-before-write operation to determine a number of cells n to be written during a write operation; comparing n to a predetermined threshold value to determine an efficient bias scheme; setting at least one voltage regulator to provide a bias voltage according to the efficient bias scheme; and performing the write operation. A method to determine threshold value to determine an efficient bias scheme of a crossbar array and an energy efficient crossbar array device are also described.