Sense Amplifier Dynamic Back Bias for Fast Sensing
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Solution Overview
Problem
Conventional sense amplifiers in DRAM with 28 nm and below semiconductor processes face slow sensing speed due to small gate overdrive voltage, often requiring ultra-low threshold voltage devices or extra masks, which increase manufacturing costs and may result in degraded read data.
Innovation Solution
A sense amplifier with an adjustable dynamic back bias, where the bulk of NMOS transistors is raised to about one third or half of the operating voltage VDD during sensing, temporarily lowering the threshold voltage and increasing current, allowing for faster operation without the need for ultra-low threshold voltage devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional sense amplifier with fixed bias is used in 28 nm and below processes, then manufacturing cost is reduced (no extra masks needed), but sensing speed becomes slow due to small gate overdrive voltage
Solution Approach 1:
The patent applies dynamic biasing by raising the bulk voltage of NMOS transistors during sensing operations. The bulk voltage is temporarily increased to about one third or half of VDD, creating a time-varying bias condition that lowers threshold voltage only when needed for fast sensing, while maintaining standard manufacturing processes without requiring ultra-low threshold voltage devices or additional masks
Solution Approach 2:
The invention changes the bulk voltage parameter of NMOS transistors from a fixed low value to a dynamically adjusted value during sensing. By modifying the bulk-to-source voltage relationship, the threshold voltage is temporarily reduced, increasing gate overdrive voltage and sensing speed without requiring process changes or additional manufacturing steps
2Speed
If ultra-low threshold voltage devices are used to increase sensing speed, then sensing speed is improved, but manufacturing cost increases due to extra masks
Solution Approach 1:
Instead of changing device characteristics through additional masks, the patent changes the operational parameter (bulk voltage) of standard transistors. This allows achieving low threshold voltage effects dynamically during sensing without requiring ultra-low threshold voltage devices, thus avoiding extra manufacturing masks and associated costs
3Speed
If gate overdrive voltage is increased to speed up sensing, then sensing speed is improved, but threshold voltage control becomes more difficult
Solution Approach 1:
The patent implements a dynamic bulk biasing scheme where the bulk voltage is raised only during sensing operations to the appropriate level (about one third or half of VDD). This temporary dynamic adjustment provides the needed gate overdrive voltage for fast sensing while automatically returning to normal bias conditions afterward, simplifying overall control compared to static high-speed designs
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
This approach enhances sensing speed, reduces manufacturing costs by omitting extra masks, and ensures quick restoration and writing of read data, preventing data degradation.
Implementation Method 1
the bulk of NMOS transistors is raised to about one third or half of the operating voltage VDD during sensing, temporarily lowering the threshold voltage and increasing current
Data Source
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AI summary
A circuit having a sensing circuit and at least one of a first node (VSSA) and a second node (VDDA) is described. The sensing circuit includes a pair of a first type transistors (N5,N6) and a pair of a second type transistors (P1,P2). Each transistor of the pair of the first type transistors (N5,N6) is coupled in series with a transistor of the pair of the second type transistors (P1,P2). The first node (VSSA) has a first voltage and is coupled to each bulk of each transistor of the pair of the first type transistors (N5,N6). The second node (VDDA) has a second voltage and is coupled to each bulk of each transistor of the pair of the second type transistors (P1,P2). During sensing, the first and second voltages are changed to reduce the threshold voltages of the pairs of first (N5,N6) and second (P1,P2) types of transistors, thereby increasing sensing speed.