Crossbar Array Current Reduction via Conductance Mapping
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Solution Overview
Problem
Crossbar array circuits with large output resistance (Rout) face challenges in achieving accurate Vector-Matrix Multiplication (VMM) due to high energy consumption and nonlinear output current, which is exacerbated by direct linear mapping of matrix values to conductance.
Innovation Solution
The method involves simulating a crossbar array circuit, calibrating a simulation model to account for device physics and circuit issues, determining a fixed ratio of ideal current, adjusting conductance mapping values, and programming the conductance matrix to reduce current while ensuring accurate computing results, using techniques such as conversion algorithms and dynamic conductance range matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct linear mapping of matrix values to crossbar conductance is used, then the conductance setting is simple, but the VMM results become inaccurate due to nonlinear output current from large Rout
Solution Approach 1:
The patent applies parameter changes by transforming the conductance mapping from a linear function to a nonlinear function that compensates for the large output resistance effect. Specifically, the conductance values are recalculated using a conversion algorithm that accounts for the voltage division between the memristor conductance and the large Rout, thereby maintaining VMM accuracy without changing the physical circuit structure.
2Loss of energy
If large output resistance (Rout) is used, then current consumption is reduced significantly, but the total current in the crossbar array circuit becomes too small for accurate computation
Solution Approach 1:
The patent uses parameter changes to adjust the conductance values of the crossbar array elements based on the large Rout present in the circuit. By applying a conversion algorithm that compensates for the voltage division effect caused by Rout, the system maintains sufficient current magnitude for accurate computation while preserving the energy-saving benefits of the large output resistance.
Solution Approach 2:
The patent incorporates feedback mechanisms through calibration processes that measure the actual current and voltage in the crossbar array circuit. These measurements are used to adjust and refine the conductance mapping values, ensuring that the compensation for Rout effects is accurate and that computing precision is maintained despite the large output resistance.
3Measurement precision
If conductance mapping values are adjusted to compensate for large Rout, then VMM accuracy is improved, but the complexity of the conductance setting process increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the conversion factors or lookup tables that map ideal conductance values to actual required conductance values accounting for the large Rout. This pre-computed conversion data is then applied during normal operation, avoiding the need for complex real-time calculations and reducing the operational complexity while maintaining accuracy.
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 significantly reduces current consumption by up to 40 times, improves computing accuracy, and dynamically adjusts conductance to match the circuit's resistance, ensuring reliable VMM operations even with large Rout values.
Implementation Method 1
An RRAM is a two-terminal passive device that is capable of changing its resistance responsive to sufficient electrical stimulations. The resistance of the RRAM may be electrically switched between two states: a High-Resistance State (HRS) and a Low-Resistance State (LRS).
Implementation Method 2
A memristor-based crossbar array circuit may perform VMMs. For instance, a crossbar array circuit may use current to do computation as I=V·G.
Data Source
AI summary
Methods of using large output resistance with adjusted conductance mapping value to reduce the current in crossbar array circuit are disclosed. An example method of simulating a crossbar array circuit having a crossbar array, includes steps of: S1. testing the crossbar array; S2. calibrating a simulation model; S3. simulating the crossbar array with the simulation model, wherein a simulation result is generated after the S3; S4. determining a fixed ratio of ideal current from the simulation result; S5. adjusting conductance mapping value to let the crossbar array pass the fixed ratio of ideal current and generating a conductance matrix; S6. programming the conductance matrix to the crossbar array; S7. passing an input signal to the crossbar array and generating a computing result; and S8. checking the quality of computing results.