Charge Trapping Memory Reference Current Adjustment
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Solution Overview
Problem
Charge trapping memory cells experience unreliability due to operation window shifts caused by charge loss after multiple cycling or data retention, which existing methods like cycling tables and extra bits cannot effectively address, especially in high-speed operations.
Innovation Solution
A charge trapping memory system with a reference current generator, sense amplifiers, and comparators that adjust the reference current based on differences between read and expected data to compensate for charge loss, ensuring accurate reading by using tracking cells and a look-up table for quick adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reading methods are used without adjustment, then the reading process is simple and fast, but the reading reliability deteriorates due to operation window shifts caused by charge loss
Solution Approach 1:
The patent performs preliminary sensing of tracking cells and adjustment of reference current before the actual memory cell reading operation. This preliminary action compensates for charge loss effects in advance, ensuring that the subsequent reading of memory cells is performed with the correct reference current for accurate threshold voltage comparison.
Solution Approach 2:
The patent uses tracking cells as copies of memory cells to monitor charge loss effects. By sensing the threshold voltage of tracking cells (which are not subjected to programming/erasing operations) and comparing with expected data, the system can determine the degree of charge loss and adjust the reference current accordingly without affecting the actual memory data.
2Reliability
If cycling tables are used to compensate for charge loss, then reading reliability improves, but the system complexity and operational overhead increase significantly
Solution Approach 1:
The patent dynamically changes the reference current parameter based on the sensed threshold voltage of tracking cells. Instead of using complex cycling tables with multiple operation conditions, the system continuously monitors tracking cell characteristics and adjusts the reference current magnitude to compensate for charge loss, simplifying the compensation mechanism to a single adjustable parameter.
Solution Approach 2:
The patent implements a feedback mechanism where the sensed data from tracking cells is compared with expected data, and the difference (indicating charge loss) is used to adjust the reference current. This closed-loop feedback continuously compensates for charge loss effects, maintaining reading reliability without requiring pre-defined cycling tables.
3Measurement precision
If extra bits are used to calculate and compare data, then reading accuracy improves, but the operation speed decreases due to multiple reading iterations
Solution Approach 1:
The patent performs the reference current adjustment in a preliminary manner before the actual memory cell reading. By sensing tracking cells and adjusting the reference current in advance, the system eliminates the need for multiple iterative readings with extra bits, achieving both high accuracy and fast operation in a single reading pass.
4Reliability
If the reference current is adjusted based on tracking cells, then the operation window shift is compensated and reading reliability improves, but the time required for current adjustment may increase
Solution Approach 1:
The patent directly adjusts the reference current parameter based on the sensed threshold voltage of tracking cells, using a continuous parameter adjustment approach rather than discrete steps. This allows for faster convergence to the correct reference current value, minimizing the time required for adjustment while ensuring accurate compensation for charge loss.
Data Source
AI summary
An accessing method for a charge trapping memory including memory cells and tracking cells for storing expected data. The method includes the following steps. In a specific time first, the expected data is written into the tracking cells and the memory cells are not being programmed, read or erased. Next, the data stored in the tracking cells is sensed as read data according to a present reference current. Then, the present reference current is adjusted to an adjusted reference current according to a difference between the read data and the expected data so that the data stored in tracking cells is sensed as corresponding with the expected data according to the adjusted reference current. Thereafter, the memory cells are read according to the adjusted reference current.