Crossbar Read Tracking Circuits for PVT-Resilient ReRAM
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Solution Overview
Problem
Crossbar arrays in ReRAM-based memory circuits are highly sensitive to process, voltage, and temperature variations, leading to increased read bit errors, especially in multi-bit configurations, due to smaller noise margins.
Innovation Solution
Incorporation of a tracking circuit with replica cells and arrays that monitor and compensate for PVT variations by generating reference voltages and compensating for leakage currents, ensuring accurate read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit ReRAM configuration is used to increase storage capacity, then the noise margin decreases leading to higher sensitivity to PVT variations, but the storage density is improved
Solution Approach 1:
The patent employs replica cells that are identical copies of the actual ReRAM cells, configured to track PVT variations. These replica cells generate compensation signals that are fed back to the read driver circuitry, effectively copying the sensitivity characteristics of the main array to enable active compensation.
Solution Approach 2:
The patent implements a feedback mechanism where the read driver circuitry continuously monitors the output of replica cells and adjusts the read voltage accordingly. This closed-loop feedback system dynamically compensates for PVT variations, maintaining the noise margin despite changes in process, voltage, or temperature conditions.
2Measurement precision
If replica cells and tracking circuits are added to compensate for PVT variations, then read accuracy is improved, but circuit complexity and area overhead increase
Solution Approach 1:
The replica cells serve multiple functions simultaneously: they track PVT variations, generate compensation signals, and validate the operation of the main array. The read driver circuitry also performs both normal read operations and compensation adjustments, reducing the need for separate dedicated compensation circuits.
Solution Approach 2:
The patent merges the tracking functionality directly into the existing crossbar array structure by using replica cells that share the same physical infrastructure (word lines, bit lines, and read driver circuitry). This integration approach eliminates the need for separate tracking circuits and reduces overall complexity.
3Measurement precision
If replica cells are used to track PVT variations in real-time, then compensation accuracy is improved, but power consumption increases
Solution Approach 1:
The tracking circuit operates periodically rather than continuously, updating compensation signals at intervals sufficient to track PVT variations without requiring constant monitoring. This periodic operation significantly reduces the average power consumption while maintaining adequate compensation accuracy for typical operating conditions.
Data Source
AI summary
Described herein are techniques to enable tracking circuits for crossbar circuits. One embodiment provides an apparatus including a crossbar array comprising: a plurality of bit lines intersecting with a plurality of word lines; and a plurality of cross-point devices, wherein each of the cross-point devices is connected to at least one of the word lines and at least one of the bit lines; a read-out circuit selectively connected to at least one of the bit lines, wherein the read-out circuit is to generate an output representative of the memristor conductance; a tracking circuit comprising a first replica cell that emulates at least one of the cross-point devices, wherein the tracking circuit is to produce a reference voltage; and a converter configured to convert the output of the read-out circuit into a digital output or a pulse-width-modulated signal, wherein the reference voltage is provided to the converter as an input.