Memory Cell Ring Oscillator PMV for Write Margin Characterization
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Solution Overview
Problem
Conventional process monitor vehicles (PMVs) are not available to monitor process variation effects on memory cell operation, which is crucial for characterizing and optimizing memory cell performance in programmable logic devices (PLDs).
Innovation Solution
A process monitor vehicle (PMV) is designed with a series of shift register bits, a logic gate, and a programmable write driver to measure the drive strength of memory cells, allowing characterization of process variation effects by simulating different transistor drive levels and measuring oscillation frequencies in a ring oscillator configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional process monitor vehicles are used, then process variation characterization is available for most PLD components, but process variation effects on memory cell operation cannot be monitored
Solution Approach 1:
The process monitor vehicle is segmented into distinct functional blocks including memory cell blocks, inverter blocks, and logic gate blocks. Each block can be independently configured and monitored, allowing specific memory cell operations to be characterized separately from other PLD components.
Solution Approach 2:
The PMV structure is designed to be universal across different memory cell types and configurations. The same PMV architecture can monitor various memory cell implementations (e.g., 6T, 8T, 10T cells) by reconfiguring the interconnect and control logic, making it adaptable to diverse memory technologies within PLDs.
2Manufacturing precision
If memory cell performance characterization is implemented, then process optimization guidance is improved, but device complexity increases
Solution Approach 1:
The PMV employs a nested structure where memory cell blocks contain embedded test logic, which in turn contains control signals and interconnect structures. This hierarchical nesting allows comprehensive monitoring functionality to be integrated within minimal additional area, as each level reuses resources from outer levels.
Solution Approach 2:
The PMV structure is self-configuring through automated test sequences that programmatically activate different memory cell blocks and measurement modes. The device performs self-diagnosis and characterization without requiring external complex test equipment, reducing overall system complexity while maintaining measurement capabilities.
Data Source
AI summary
A method and apparatus is provided for the implementation of a process monitor vehicle (PMV) for memory cells. The memory cell PMV is useful in characterizing drive strength of the N-type and P-type field effect transistors (FETs) that are used to implement the memory cell. The memory cell PMV may be used, for example, to measure the amount of margin available for memory cell flips and how process variation affects the memory cell write margin. The memory cell PMV is implemented as a plurality of shift register bits interconnected as a ring oscillator, where each shift register bit is comprised of a memory cell. By adjusting the drive current for each memory cell and measuring the resultant change in oscillation frequency of the ring oscillator, information may be obtained concerning process variation and its effect on memory cell performance.