Robust SRAM Designs and Analysis: A Comprehensive Guide for Engineers

The two transistors M1 and M2 form the cross-coupled inverters, while the transistors M3 and M4 serve as access transistors. When the word line (WL) is asserted, the access transistors M3 and M4 turn on, allowing data to be read from or written to the cell. The data is stored in the form of a charge imbalance on the internal nodes of the cell.

The stability of an SRAM cell is determined by the ratio of the strengths of the access transistors M3 and M4 to the strengths of the cross-coupled inverters M1 and M2. If the access transistors are too strong, the cell may be inadvertently written during a read operation. Conversely, if the cross-coupled inverters are too strong, the cell may lose its data during a write operation.

SRAM Layout

The layout of an SRAM cell is critical to its stability and performance. The following factors should be considered when designing the layout of an SRAM cell:

• Symmetry: The layout of the cell should be symmetrical to minimize the effects of process variations and noise.
• Spacing: The spacing between the transistors should be carefully controlled to minimize the risk of electrostatic discharge (ESD) and other reliability issues.
• Interconnect: The interconnect between the transistors should be designed to minimize the resistance and capacitance of the cell.

SRAM Analysis

The analysis of an SRAM cell is essential to ensure its stability and reliability. The following techniques can be used to analyze SRAM cells:

• Static analysis: Static analysis can be used to determine the stability of an SRAM cell under worst-case conditions. This involves calculating the noise margins of the cell and ensuring that they are sufficiently large.
• Dynamic analysis: Dynamic analysis can be used to simulate the behavior of an SRAM cell over time. This can be used to identify potential problems with the cell, such as write-disturb and read-disturb errors.
• Layout verification: Layout verification can be used to ensure that the layout of an SRAM cell is correct and meets the design specifications.

SRAM design and analysis is a complex and challenging task. However, by following the techniques described in this article, engineers can design and implement robust SRAM cells that meet the requirements of their applications.

For more information on this topic, please refer to the following resources:

• Robust SRAM designs a must for advanced process nodes
• New SRAM cell design mitigates variability, improves yield and stability
• Analysis and Design of SRAM Cells for Low-Power and High-Stability