Memory Cell Self-Diagnosis Using Fixed-Value Readback
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Solution Overview
Problem
Existing memory devices, such as OTP ROMs, lack effective self-diagnosis functions for ensuring functional safety and efficient data storage and retrieval, particularly in applications like vehicle power supply systems.
Innovation Solution
A memory device with integrated self-diagnosis functionality, utilizing a matrix of memory cells and peripheral circuits, including a controller, DC/DC converters, and a detector, that stores fixed values for self-testing and ensures accurate data reading and writing by comparing actual values with expected values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If self-diagnosis functionality is integrated into the memory device, then functional safety is enhanced, but device complexity increases
Solution Approach 1:
The self-diagnosis function is merged with the existing memory device structure by utilizing the controller and detector circuits that are already present for normal memory operations. The controller executes self-diagnosis routines using the same data input/output circuits and bit detectors, combining diagnostic capabilities with the core memory functionality without adding separate dedicated diagnostic hardware.
Solution Approach 2:
The controller and detector circuits are designed to serve multiple functions: they handle both normal memory read/write operations and self-diagnosis operations. The data input/output circuits and bit detectors are used universally for both external data access and internal self-testing, eliminating the need for separate dedicated diagnostic components.
2Measurement precision
If fixed values are stored in memory cells for self-testing, then measurement precision is improved, but manufacturing precision requirements increase
Solution Approach 1:
Fixed test values are pre-stored in specific memory cells during the manufacturing process before the device is deployed. These predetermined values serve as reference data for self-diagnosis operations, allowing the device to perform accurate fault detection without requiring high-precision manufacturing of the test data itself, as the values are established in advance.
Solution Approach 2:
The self-diagnosis function uses copied or replicated fixed values stored in memory cells as reference data for comparison during testing. By storing multiple copies of known good values in the memory array, the system can accurately detect faults by comparing actual readings against these pre-stored reference copies, reducing the burden on manufacturing precision.
Data Source
AI summary
A memory device includes: a word line selector (X decoder) configured to select word lines; a memory cell having cells that are connected to the word lines and to bit line units so as to be arrayed in a matrix; a bit detector configured to detect, via the bit line units, the logic values of the bit data stored in the cells connected to a selected word line; a data output circuit configured to output data based on the results of detection by the bit detector; and a controller. Fixed values are stored in part of the cells corresponding to a predetermined number of bits, and the controller compares, with expected values, the fixed values read from the part of the cells via the bit detector and the data output circuit.