SRAM Keeper Circuit Polarity Shift for Lower Bit Line Area

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Solution Overview

Problem

Existing SRAM technologies require a substantial number of p-type transistors for keeper circuits, leading to undesired area overhead.

Innovation Solution

Implementing a memory circuit with a keeper circuit and a pre-charge circuit that utilize transistors of opposite conductive types, such as n-type and p-type, to reduce area overhead.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If p-type transistors are used for keeper circuits in SRAM, then the keeper circuit can maintain bit line voltage levels, but the area overhead increases substantially

Engineering Contradiction:

Improvebit line voltage level maintenanceVSAvoidkeeper circuit area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent changes the key parameter of transistor conductive type from p-type to n-type for the keeper circuit. This parameter change allows the keeper circuit to maintain bit line voltage levels effectively while occupying substantially less area, thus resolving the contradiction between reliability and area overhead.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using p-type transistors as conventionally done in keeper circuits, the patent inverts the approach by using n-type transistors. This inversion enables the keeper circuit to achieve its voltage maintenance function with reduced area, addressing both the reliability requirement and the area overhead concern.

Inventive Principle:

Principle #13The other way round (Inversion)

2Stability of the object's composition

If more transistors are used in keeper circuits, then voltage level stability improves, but integration density decreases

Engineering Contradiction:

Improvevoltage level stabilityVSAvoidintegration density

Core Design Contradiction:

Stability of the object's compositionVSProductivity

Solution Approach 1:

By changing the transistor conductive type parameter from p-type to n-type in the keeper circuit, the patent achieves voltage level stability with fewer transistors. This parameter change enables better integration density while maintaining the required voltage stability during read operations.

Inventive Principle:

Principle #35Parameter changes

3Area of stationary object

If n-type transistors are used for keeper circuits, then area overhead is reduced, but the ability to maintain voltage levels during read operations may be affected

Engineering Contradiction:

Improvekeeper circuit areaVSAvoidvoltage level maintenance

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent successfully changes the transistor conductive type to n-type while maintaining voltage level maintenance capability. The n-type keeper circuit is designed with appropriate sizing and configuration to ensure it can effectively maintain bit line voltage levels during read operations, thus achieving area reduction without compromising reliability.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20260051350A1Memory circuits with keeper circuits and methods for operating the same

Publication Date: 2026.02.19 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A memory circuit includes a plurality of memory cells commonly coupled to a bit line. The memory circuit includes a pre-charge circuit coupled to the bit line, and comprising one or more first transistors with a first conductive type. The memory circuit includes a keeper circuit coupled to the bit line, and comprising one or more second transistors with a second conductive type.