Self-reference sense amplifier circuit for flash memory
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Solution Overview
Problem
Conventional flash memory devices have large size issues due to separate provision of reference voltage generators and suffer from errors caused by ineffective electrical connections and differences in current driving capabilities between main and dummy memory cells.
Innovation Solution
A sense amplifier circuit with a self-reference capability, utilizing different current driving capabilities between transistors controlled by selected and unselected bit lines, eliminates the need for a separate reference voltage generator by using a precharge voltage as a reference, thereby reducing size and improving operational stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate reference voltage generator is provided on a different part of the substrate, then the sense amplifier can perform voltage comparison, but the overall device size increases
Solution Approach 1:
The reference voltage generation function is merged with the memory cell array by using dummy memory cells located within the same substrate region as the main memory cells. This eliminates the need for a separate reference voltage generator circuit, thereby reducing overall device size while maintaining sensing stability through proper voltage comparison capability.
Solution Approach 2:
The dummy memory cells serve multiple functions: they generate the reference voltage Vref needed by the sense amplifier, they are located within the memory cell array region to minimize area overhead, and they undergo the same programming and erasing operations as main memory cells to ensure matched characteristics. This multi-functionality resolves the contradiction between reliability and device size.
2Reliability
If dummy cells are disposed in a different region from main memory cells, then reference voltage can be generated, but electrical connections become ineffective causing errors
Solution Approach 1:
The dummy memory cells are strategically located within the same substrate region as the main memory cells, specifically in regions that share the same bit line connections. This local positioning ensures that the dummy cells experience the same electrical environment, process variations, and connection qualities as the main memory cells, thereby eliminating sensing accuracy errors caused by ineffective electrical connections while maintaining reference voltage generation capability.
3Ease of operation
If dummy cells are used to generate reference voltage, then the sense amplifier can operate, but differences in current driving capabilities cause mismatches
Solution Approach 1:
The dummy memory cells are programmed and erased in advance along with the main memory cells during normal memory operations. This preliminary action ensures that the threshold voltages of dummy cells closely match those of main memory cells before they are used to generate reference voltage, thereby minimizing mismatches in current driving capabilities and improving manufacturing precision.
Solution Approach 2:
The sense amplifier uses the dummy memory cells to generate a reference voltage that is continuously adjusted based on the actual state of main memory cells. By comparing the current driving capabilities and adjusting the reference accordingly, the system compensates for process variations and maintains high manufacturing precision in sensing operations.
Data Source
AI summary
A sense amplifier circuit for a flash memory device is disclosed. The sense amplifier including a first transistor controlled by a first voltage applied via a selected bit line, and a second transistor controlled by a second voltage applied via an unselected bit line. The second transistor has a current driving capability lower than a current driving capability of the first transistor.