SRAM Word Line Overdrive Using Capacitor-Boosted Write Assist
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Solution Overview
Problem
Static random-access memory (SRAM) circuits face challenges in maintaining operating margins and reducing power consumption due to the lossy charging and discharging of bit lines and word lines, leading to potential memory errors and increased power usage.
Innovation Solution
Implementing a write assist circuit with an overvoltage generator (OVG) that charges a capacitor to a higher voltage than the word line driver, coupling it with the word line to enhance operating margins and reduce power consumption by selectively asserting different voltages based on operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If word line driver asserts word line to standard voltage, then memory cell operation is maintained, but operating margin decreases and memory errors increase
Solution Approach 1:
The system dynamically adjusts word line voltage based on operating conditions. The overvoltage generator is selectively activated to provide elevated voltage (e.g., 1.2V-1.8V above standard voltage) when operating margins are compressed due to temperature variations or process variations, while maintaining standard voltage during normal operation. This dynamic voltage adjustment resolves the contradiction by improving reliability only when needed, rather than continuously increasing voltage.
Solution Approach 2:
The patent changes the voltage parameter of the word line based on operating conditions. The controller monitors parameters such as temperature and process variations, and adjusts the word line voltage accordingly by activating the overvoltage generator. This parameter change allows the system to maintain adequate operating margins without permanently increasing device complexity.
2Reliability
If overvoltage generator charges capacitor to higher voltage, then operating margin increases, but power consumption increases
Solution Approach 1:
The overvoltage generator operates periodically rather than continuously. It is activated only during specific write operations when operating margins are compressed, and deactivated during normal read operations or when voltage margins are adequate. This periodic activation significantly reduces average power consumption while still providing the reliability benefits when needed.
Solution Approach 2:
The capacitor is pre-charged to the elevated voltage level before the write operation begins. The overvoltage generator charges the capacitor in advance, and then the capacitor discharges to provide the boosted voltage to the word line during the critical write window. This preliminary charging action ensures that the high voltage is available exactly when needed, minimizing the time the overvoltage generator is active and thus reducing power consumption.
3Productivity
If word line driver continuously drives word line, then write operations are completed, but power consumption increases
Solution Approach 1:
The overvoltage generator pre-charges the capacitor before the write operation, so that when the write is needed, the voltage is already boosted and ready. This eliminates the need for the word line driver to continuously maintain high drive strength, as the capacitor provides the voltage boost during the critical write window. The driver only needs to provide the initial charge and then can be decoupled, reducing continuous power consumption.
Solution Approach 2:
The capacitor acts as an intermediary energy storage element between the overvoltage generator and the word line. Instead of the word line driver continuously supplying high voltage, the capacitor stores the energy and releases it during the write operation. This intermediary approach allows the driver to be decoupled from the word line during the write, reducing the driver's power consumption while still achieving fast write operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The OVG enhances memory cell operation by increasing voltage margins, reducing memory errors, and optimizing power usage by dynamically adjusting voltage levels according to temperature and timing requirements.
Implementation Method 1
an overvoltage generator to charge a capacitor. The controller is configured to couple the overvoltage generator with the capacitor to charge the capacitor to a voltage exceeding the first voltage
Implementation Method 2
couple the capacitor with the word line to assert the word line to the voltage in excess of the first voltage
Data Source
AI summary
A memory circuit includes memory cells commonly coupled to a word line, a word line driver, an overvoltage generator, and a memory controller. The word line driver is selectively coupled to the word line to assert the word line to a first voltage. The memory controller can couple the word line driver with the word line to assert the word line to the first voltage. The memory controller can decouple the word line driver from the word line to maintain the word line at the first voltage. The memory controller can couple the overvoltage generator with the capacitor to charge the capacitor to a second voltage. The memory controller can couple the capacitor with the word line to assert the word line to the second voltage. The memory controller can write a data value to a memory cell with the word line driven to the second voltage.