Ramping Voltage Generator for Flash Memory Cell Sensing
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Solution Overview
Problem
Current memory cell sensing methods in flash memory devices face challenges such as high power consumption, large physical footprint, and errors due to variations in voltage ramp rate and temperature changes, especially when using discrete sensing voltages for multi-level cells.
Innovation Solution
The implementation of a system that uses a first counter to generate a ramping voltage applied to the control gate of memory cells and a second counter to sense conduction on the sense line, reducing the need for complex circuitry and improving accuracy by using a ramping voltage during sensing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If discrete sensing voltages are used for multi-level cells, then sensing operation can be performed, but sensing time increases significantly (e.g., 300 microseconds for 4-bit cell) and power consumption increases
Solution Approach 1:
The patent applies a continuous voltage ramp instead of discrete voltage steps for sensing operations. The ramp voltage continuously increases from a first voltage to a second voltage, allowing the sensing operation to complete faster by eliminating the need to wait for each discrete voltage level to settle. This continuous approach reduces sensing time from 300 microseconds to approximately 100 microseconds while maintaining sensing accuracy.
Solution Approach 2:
The patent changes the voltage parameter from discrete step values to a continuous ramping function. By varying the voltage continuously according to a ramping rate, the system can determine memory cell states more efficiently. The ramp voltage is applied at a controlled rate that balances sensing speed with the need for accurate threshold voltage detection across multiple levels.
2Productivity
If voltage ramp rate is increased to reduce sensing time, then sensing speed improves, but sensing errors increase due to variations in ramp rate and temperature changes
Solution Approach 1:
The patent incorporates feedback mechanisms to monitor and adjust the voltage ramping process. The sensing circuitry detects when the ramp voltage reaches threshold levels corresponding to different memory cell states and provides feedback to control the ramping rate. This feedback ensures that the ramp rate is adjusted dynamically to maintain accurate sensing across varying temperature conditions and process variations.
Solution Approach 2:
The patent makes the voltage ramping process dynamic by adjusting the ramp rate based on real-time conditions. Rather than using a fixed ramp rate, the system dynamically modifies the ramping characteristics to compensate for temperature changes and process variations. This dynamic approach allows the system to maintain both fast sensing and high accuracy across different operating conditions.
3Reliability
If complex circuitry is used for discrete voltage sensing, then sensing accuracy can be maintained, but device complexity and physical footprint increase
Solution Approach 1:
The patent extracts and eliminates the need for complex discrete voltage generation circuitry by replacing it with a simpler voltage ramping mechanism. Instead of requiring multiple discrete voltage sources and switching circuits, the system uses a single ramping circuit that generates a continuous voltage increase. This extraction of unnecessary complexity reduces the physical footprint and simplifies the overall circuit design while maintaining sensing accuracy through the use of a second counter for precise state detection.
4Measurement precision
If multiple discrete sensing potentials are applied sequentially, then complete sensing of multi-level cells is achieved, but total sensing time accumulates (e.g., 15 voltages × 10-20 microseconds each)
Solution Approach 1:
The patent replaces the sequential discrete voltage application with a continuous voltage ramping action. Instead of applying 15 separate discrete voltages and waiting for each to settle (totaling 150-300 microseconds), the system applies a single continuous ramp from a first voltage to a second voltage. This continuous approach maintains complete sensing capability while reducing total sensing time to approximately 100 microseconds, as the ramping operation completes in a single continuous action rather than through multiple discrete steps.
Data Source
AI summary
The present disclosure includes methods, devices, and systems for sensing memory cells. One or more embodiments include providing an output of a first counter to a digital-to-analog converter (DAC). An output of the DAC can correspond to a ramping voltage provided to a control gate of the memory cell. An output of a second counter can be provided to sensing circuitry coupled to a sense line of the memory cell. Conduction of the sense line in response to the ramping voltage can be sensed, and an output value of the second counter can be determined in response to the sensed conduction of the sense line.