Cross-Coupled Resistive Memory Read Method
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Solution Overview
Problem
Resistive random access memory (ReRAM) and conductive bridging random access memory (CBRAM) cells face challenges in reliably reading their resistance values, especially when they change due to previous read operations or poor data retention, leading to disturbance of the memorized conductive state.
Innovation Solution
A cross-coupled read method and system using two resistive memory devices in a degenerated current mirror circuit, where the trip point is adaptively set between the logic one and zero states, minimizing disturbance and allowing for accurate reading even with small differences in resistance values, and enabling low-frequency read operations without a fixed voltage reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a unipolar read operation is used to read the state of the memory cell, then the memory cell state can be read, but the memorized resistance value of the memory cell will be disturbed
Solution Approach 1:
The patent applies differential reading by inverting the conventional approach: instead of reading one memory cell against a fixed reference, two memory cells are read differentially against each other. One cell is selected for reading while the other serves as a complementary reference, both subjected to the same read voltage. This inversion of the reference concept eliminates disturbance issues because neither cell acts as a fixed reference that could be destabilized by the read operation.
Solution Approach 2:
The patent changes the reading parameter from unipolar (single-ended) to differential mode. By applying the read voltage across both selected and complementary memory cells simultaneously and comparing their current outputs, the system achieves accurate state reading without disturbing the memorized resistance values, as both cells experience identical voltage stress.
2Measurement precision
If the resistance value of the resistive memory element changes due to previous read operations or poor data retention, then reading accuracy deteriorates, but using a fixed voltage reference requires calibration
Solution Approach 1:
The patent implements self-calibration through the differential architecture. The complementary memory cell automatically serves as a dynamic reference that adapts to resistance value changes in the selected cell. Since both cells are subjected to the same read conditions, any drift or change in resistance values is automatically compensated for in the differential comparison, eliminating the need for external calibration circuits or procedures.
Solution Approach 2:
The patent transitions from a static fixed voltage reference to a dynamic adaptive reference system. The complementary memory cell's resistance value dynamically adjusts based on the selected cell's state, providing a moving reference point that maintains reading accuracy even when resistance values drift due to previous operations or retention issues.
3Reliability
If both memory cells have very small differences in resistance values, then it becomes difficult to distinguish the data state, but increasing the resistance difference may require higher read voltage that disturbs the cell state
Solution Approach 1:
The patent employs feedback through the cross-coupled latch circuit that captures the differential current output. The latch circuit provides regenerative feedback that amplifies small current differences resulting from small resistance variations, enabling reliable data state distinction without requiring large resistance differences or high read voltages that would disturb the cell states.
Solution Approach 2:
The patent uses the complementary memory cell as a counterweight to the selected cell in the differential measurement. By subtracting the current from one cell from the other, the system creates a balanced measurement where small resistance differences produce measurable current differences without requiring excessive read voltage, thus avoiding disturbance to the cell states.
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 maximizes data retention and ensures correct reading of resistive memory cells by maintaining a stable window between resistance states, reducing disturbance and the need for calibration, and can be implemented in microcontroller designs for efficient fuse reading.
Implementation Method 1
ReRAM and CBRAM like memory cells change their conductive state when an external electric field is applied thereto
Implementation Method 2
two resistive memory devices in a degenerated current mirror circuit, where the trip point is adaptively set between the logic one and zero states
Data Source
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AI summary
By arranging both a conductive and non-conductive resistive memory cell in a cross coupled arrangement to facilitate reading a data state the memory cells can have very small differences in their resistance values and still read correctly. This allows both of the memory cells' resistances to change over time and still have enough difference between their resistances to read the desired data state that was programmed. A pair of ReRAM or CBRAM resistive memory devices are configured as a one bit memory cell and used to store a single data bit wherein one of the resistive memory devices is in an ERASE condition and the other resistive memory devices of the pair is in a WRITE condition. Reading the resistance states of the resistive memory device pairs is accomplished without having to use a reference voltage or current since a trip-point is between the conductive states thereof.