Voltage-Divider Weighted-Sum Circuit With Constant Output Impedance
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Solution Overview
Problem
Existing electronic circuits for calculating weighted sums in neuromorphic hardware face issues such as high current densities, noise, process and temperature variations, and inefficiencies in current-to-voltage conversion, particularly when handling both positive and negative weights.
Innovation Solution
An electronic circuit with a crossbar architecture using voltage divider circuits for setting weight factors, ensuring constant impedance and local current cancellation, outputting weighted sums as differential voltages to avoid current-related issues and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a crossbar architecture with current-based computation is used, then in-memory computing performance is improved, but high current densities and noise issues occur
Solution Approach 1:
The patent replaces the conventional current-based computation mechanism with a voltage-based computation mechanism. Instead of using current to represent and compute weight values, the invention uses voltage dividers where voltage represents the weight and the computation is performed through voltage division and summation. This substitution eliminates the high current density and associated noise problems while maintaining the in-memory computing performance.
2Ease of operation
If current-to-voltage conversion is performed at the output, then the weighted sum can be read out, but conversion inefficiencies and additional circuit area are introduced
Solution Approach 1:
The patent extracts the voltage conversion function from the output stage and integrates it directly into the computational units (neurons). Each neuron computes its output voltage directly through voltage division and summation operations, eliminating the need for separate current-to-voltage conversion circuits at the output. This reduces circuit area and conversion inefficiencies while maintaining full readout capability.
3Adaptability or versatility
If both positive and negative weights are supported, then general weighted sum calculation is achieved, but circuit complexity increases
Solution Approach 1:
The patent handles negative weights by inverting the conventional approach. Instead of using separate circuits or complex switching mechanisms for negative weights, the invention represents negative weights as positive voltage values and uses the inverting input of the summing amplifier to achieve the negative contribution. This simplifies the circuit structure while maintaining full capability for both positive and negative weights.
4Use of energy by moving object
If analog multiplication is used for limited accuracy, then energy efficiency is improved, but sensitivity to process and temperature variations increases
Solution Approach 1:
The patent addresses sensitivity to process and temperature variations by changing the reference parameter from absolute voltage levels to voltage ratios. The voltage divider circuits use matched resistor pairs where the weight is determined by the ratio of resistances rather than absolute values. This ratio-based approach compensates for process and temperature variations that affect both resistors equally, maintaining reliability while preserving energy efficiency through analog computation.
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
The proposed circuit reduces power consumption, minimizes area requirements, and is less sensitive to temperature and process variations, providing accurate weighted sum calculations without input overflow or nonlinearity.
Implementation Method 1
allowing to set at least one of said weight factors by a ratio of at least two resistances
Implementation Method 2
several coupling units connecting the input lines to the output lines, each of the coupling units providing at least one individual weight factor
Data Source
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AI summary
An electronic circuit for calculating weighted sums of input voltages comprises several input lines to which the input voltages are applied, and at least one summation unit. The summation unit is formed of a first and a second output line, several first coupling units connecting the input lines to the first output line and several second coupling units connecting the input lines to the second output line. Each of the coupling units provides one or several individual weight factors for weighted coupling an input voltage on the corresponding input line to the corresponding output line. The electronic circuit is characterized in that each of the first and second coupling units comprises at least one voltage divider circuit, referenced to a common input potential, said voltage divider circuit allowing to set at least one of said weight factors by a ratio of at least two resistances. The voltage divider circuits are arranged and/or controlled such that an impedance seen from each output line into any of the coupling units stays constant independent on the weight factors set.