MBIST in VLSI: Ensuring Better Quality Chips

MBIST in VLSI: Ensuring Better Quality Chips

In modern SoCs, embedded memory takes up the majority of the chip space and incorporates an even greater number of active devices. Because memories are meant to be exceedingly dense to the limitations of technology, faults may occur. Moreover, when fault types become more complex and diversified, they may escape detection during testing.

Memory test techniques should evolve to address the flaws associated with the target manufacturing process and memory design. Hence, MBIST (Memory Built-In Self Test) is a crucial aspect of VLSI design and testing.

In modern-day electronics, the quality and reliability of memories like RAM, ROM, and other memory chips play a significant role in the functioning of electronic devices. Hence, the testing of memory chips has become a critical step in the manufacturing and testing of electronic systems. MBIST is an efficient method for testing memories and ensuring their functionality.

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What is MBIST in VLSI?

MBIST is a self-testing method incorporating a self-test circuit within the memory chip. The self-test circuit is designed to write a test pattern to the memory, read it back, and compare the results with the expected results. The self-test circuitry includes test pattern generators, output comparators, and control circuitry. It is a valuable tool for ensuring the quality and reliability of memory chips, which play a significant role in the functioning of electronic devices. The MBIST technique allows the testing of memory chips during manufacturing and operation, ensuring that any defects or faults are detected and corrected in a timely manner. This results in better quality and reliability of electronic systems, which are critical for various applications in today’s world.

How Does It Work?

The MBIST technique is used during manufacturing to test memory chips for defects and errors that may have occurred during fabrication. The self-test circuitry allows the testing of the memory cells in isolation from the rest of the circuitry. The memory cells are tested by writing a test pattern and reading it back to ensure that it matches the expected result. Any discrepancies between the expected and actual results are used to detect faults in the memory cells. In case of any discrepancies, the chip is repaired, or if the error is significant, it is discarded.

Architecture of MBIST In VLSI

The MBIST architecture is an essential component of VLSI design and testing. It allows for the efficient and accurate testing of memory chips during manufacturing and operation, ensuring their quality and reliability. The architecture includes a test pattern generator, a data comparator, a control unit, and a memory array, which work together to detect faults in the memory chips and take corrective action if necessary.

Also Read Types of Testing in Design for Testability?

Test Pattern Generator: 

The test pattern generator generates a sequence of test patterns to be written to the memory array. The test patterns are designed to exercise all possible memory cell states, ensuring that every possible fault is detected. 

Data Comparator: 

The data comparator compares the read data from the memory array with the expected data generated by the test pattern generator. If the read data does not match the desired data, it indicates a fault in the memory array.

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Control Unit: 

The control unit controls the test process and generates the necessary control signals for the test pattern generator and data comparator. 

Memory Array: 

The memory array is the actual memory device being tested. It is typically a set of memory cells arranged in rows and columns, with each cell capable of storing a single bit of data.

Conclusion

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