Write Driver Pre-Emphasis for Variable Resistance Memory
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Solution Overview
Problem
In variable resistance memory elements, the overshoot phenomenon occurs due to the resistance state of cells, leading to inefficient data writing as the required current is not adequately transferred, necessitating repeated program and verify processes.
Innovation Solution
A write driver is configured to determine the magnitude and application time of a pre-emphasis current pulse based on parasitic components and the resistance value of the target cell, adding this current to the preset program current to improve data writing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If only time constant determined according to path from write driver to cell is considered for program current pulse compensation, then current transfer is improved, but overshoot phenomenon occurs according to resistance state of cell before program
Solution Approach 1:
The patent applies preliminary action by performing a pre-read operation before the program operation to obtain the resistance value of the target cell. Based on this pre-obtained resistance value, the system determines appropriate pre-emphasis current parameters (magnitude and application time) in advance, allowing the system to compensate for cell-specific characteristics before the actual programming occurs, thereby preventing overshoot while ensuring adequate current transfer.
Solution Approach 2:
The patent changes parameters by adjusting both the magnitude and application time of the pre-emphasis current pulse based on the pre-read resistance value. The controller dynamically modifies these parameters according to the specific resistance state of the target cell, enabling precise control that adapts to different cell conditions and eliminates the overshoot phenomenon while maintaining reliable current transfer.
2Productivity
If program current pulse is not adequately compensated, then device complexity is reduced, but repeated program and verify processes are required
Solution Approach 1:
The patent implements feedback by using the pre-read resistance value of the target cell to determine the appropriate pre-emphasis current parameters. This feedback mechanism allows the system to adjust the program current pulse characteristics based on the actual state of the target cell, ensuring that the programming operation is performed optimally in a single attempt, thereby improving writing efficiency and eliminating the need for repeated program and verify cycles.
3Reliability
If pre-emphasis current with determined magnitude and application time is added to program current, then current transfer to target cell is improved, but device complexity increases
Solution Approach 1:
The patent reduces the apparent complexity of the write driver by performing the complex calculation and determination of pre-emphasis current parameters in advance through a pre-read operation. The controller determines the magnitude and application time of the pre-emphasis current based on the pre-obtained resistance value before the actual program operation, allowing the write driver to simply execute a predetermined sequence of operations rather than performing complex real-time calculations.
Data Source
AI summary
A write driver is configured to determine a magnitude and an application time of a pre-emphasis current pulse in response to control codes generated according to parasitic components on a path from a write driver to a program target cell and a resistance value of the program target cell, and supply a preset program current to a memory circuit block by adding a pre-emphasis current to the preset program current in a program mode.