SRAM Write Assist Circuit for Dummy Write Prevention
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Solution Overview
Problem
Static random access memory (SRAM) cells experience dummy write issues due to threshold voltage fluctuations in pass gate transistors, leading to unintended changes in binary content during write operations, particularly exacerbated by temperature fluctuations and fabrication process variations.
Innovation Solution
A write assist circuit is implemented to provide a reference voltage to SRAM cells, including a boost circuit and an adjustment circuit to compensate for threshold voltage deviations, ensuring that unselected SRAM cells maintain their binary content by reducing the voltage difference between the pass gate transistor's gate and bitline, thereby preventing leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a write assist circuit is implemented to provide reference voltage to SRAM cells, then reliability is improved by preventing dummy write issues, but device complexity increases due to additional boost circuit and adjustment circuit components
Solution Approach 1:
A write assist circuit is introduced as an intermediary component between the write driver and SRAM cells. This circuit includes a boost circuit that generates a negative voltage and an adjustment circuit that regulates this voltage to compensate for threshold voltage variations in pass gate transistors, thereby preventing dummy write issues without requiring fundamental changes to the SRAM cell structure
Solution Approach 2:
The write assist circuit dynamically adjusts the reference voltage parameter provided to the SRAM cells during write operations. By changing the voltage level adaptively based on detected threshold voltage deviations, the circuit compensates for process variations and temperature effects, ensuring reliable write operations across different operating conditions
2Manufacturing precision
If adjustment circuit is used to compensate for threshold voltage deviations, then manufacturing precision is improved by maintaining binary content integrity, but device complexity increases due to additional voltage adjustment components
Solution Approach 1:
The adjustment circuit implements a feedback mechanism that monitors the threshold voltage of pass gate transistors and dynamically adjusts the reference voltage accordingly. This closed-loop control ensures that voltage compensation is applied only when needed, maintaining binary content integrity while avoiding unnecessary complexity in normal operating conditions
Solution Approach 2:
The boost circuit performs preliminary voltage generation by creating a negative voltage before the actual write operation. This pre-adjusted voltage is then fine-tuned by the adjustment circuit, allowing the system to proactively compensate for expected threshold voltage deviations rather than reacting to errors after they occur
Data Source
AI summary
The present disclosure describes embodiments of a write assist circuit. The write assist circuit can include a boost circuit configured to output a first negative voltage at a fist output terminal, and an adjustment circuit configured to couple the first negative voltage to a second negative voltage higher than the first negative voltage. The adjustment circuit can include a transistor, and a second output terminal electrically connected to the first output terminal. The transistor can include a first source/drain terminal, a second source/drain terminal, and a gate terminal. The first source/drain terminal can be electrically coupled to the second output terminal. The second source/drain terminal can be electrically connected to a voltage source. The gate terminal can be electrically connected to a ground voltage supply.