Parallel Reference Cells for MRAM Sense Amplifier Read Error Reduction
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Solution Overview
Problem
Conventional resistive based memory devices, such as MRAM, experience significant read error rates due to variations in resistance values of reference cells, leading to fluctuations in reference currents and incorrect data reading.
Innovation Solution
The solution involves coupling multiple reference cells in parallel across different columns, allowing each sense amplifier to access a broader range of resistive elements, thereby averaging and reducing resistance variations, and utilizing a 'reverse-connected' configuration for read operations to minimize disturbances during data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single reference cell is used in conventional MRAM, then the structure is simple, but resistance variations cause huge current fluctuations and large read error rates
Solution Approach 1:
Multiple reference cells (first reference cell and second reference cell) are merged in parallel to form a combined reference structure. This parallel configuration allows the sense amplifier to access multiple reference elements, averaging out resistance variations and reducing read error rates from 4% to 0.8% while maintaining structural integration within the memory device
Solution Approach 2:
The reference cell function is segmented into multiple independent reference elements (first reference cell with first resistive element, second reference cell with second resistive element). Each reference element can be independently accessed by the sense amplifier, allowing parallel measurement and reducing the impact of individual element variations on overall read accuracy
2Measurement precision
If resistance variations are present in reference cells, then manufacturing is easier, but current fluctuations increase and measurement precision deteriorates
Solution Approach 1:
Multiple reference cells are merged in parallel to create a distributed reference structure. This allows the system to tolerate individual cell variations while achieving better measurement precision through averaging, without requiring ultra-precise manufacturing of each individual reference element
Solution Approach 2:
The sense amplifier incorporates feedback mechanisms to compare currents from multiple reference elements and adjust measurements accordingly. This feedback loop compensates for resistance variations in individual cells, maintaining measurement precision even when manufacturing variations exist
3Reliability
If conventional read operation is used, then the operation is simple, but disturbances occur during data retrieval and read errors increase
Solution Approach 1:
The read operation is segmented into separate phases: first reading data from the memory cell, then reading reference values from the reference cells. This segmentation allows the sense amplifier to process reference information after the main data read, minimizing disturbances to the memory cell during the critical data retrieval phase
Solution Approach 2:
The system performs preliminary reference cell readings after the main data read operation. By separating the reference measurement timing from the data read timing, the invention avoids disturbances to the memory cell while still providing accurate reference values for error correction
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 variations in reference currents, decreasing read error rates from 4% to 0.8% and maintaining accurate resistance values, enhancing the reliability of data reading in memory devices.
Implementation Method 1
variations of resistances of elements induce huge fluctuation in the current
Implementation Method 2
converting a current difference caused by the resistance of the magnetoresistive element into a difference of the voltage drop of a transistor in the sense amplifier
Data Source
AI summary
A memory device includes a plurality of sense amplifiers, a plurality of memory cells, a plurality of data lines, a plurality of reference cells, and a connection line. The memory cells are coupled to a plurality of first inputs of the plurality of sense amplifiers respectively. The data lines are coupled to a plurality of second inputs of the plurality of sense amplifiers respectively. The reference cells are arranged in a plurality of columns respectively and coupled to the plurality of data line respectively. Each of the plurality of reference cells includes a plurality of resistive elements. The connection line is coupled to the plurality of data lines. In a read mode, one of the sense amplifiers is configured to access the plurality of resistive elements arranged in at least one of the plurality of columns.