Managing Device Lifecycle: Reconfigurable Constrained Codes for M/T/Q/P-LC Flash Memories

01/08/2020
by   Ahmed Hareedy, et al.
0

Flash memory devices are winning the competition for storage density against magnetic recording devices. This outcome results from advances in physics that allow storage of more than one bit per cell, coupled with advances in signal processing that reduce the effect of physical instabilities. Constrained codes are used in storage to avoid problematic patterns. Recently, we introduced binary symmetric lexicographically-ordered constrained codes (LOCO codes) for data storage and data transmission. This paper introduces simple constrained codes that support non-binary physical substrates; multi, triple, quad, and the currently-in-development penta-level cell (M/T/Q/P-LC) Flash memories. The new codes can be easily modified if problematic patterns change with time. These codes are designed to mitigate inter-cell interference, which is a critical source of error in Flash devices. The occurrence of errors is a consequence of parasitic capacitances in and across floating gate transistors, resulting in charge propagation from cells being programmed to the highest charge level to neighboring cells being programmed to lower levels. The new codes are called q-ary asymmetric LOCO codes (QA-LOCO codes), and the construction subsumes codes previously designed for single-level cell (SLC) Flash devices (A-LOCO codes). QA-LOCO codes work for a Flash device with any number, q, of levels per cell. For q ≥ 4, we show that QA-LOCO codes can achieve rates greater than 0.95 log_2 q information bits per coded symbol. The complexity of encoding and decoding is modest, and reconfiguring a code is as easy as reprogramming an adder. Capacity-achieving rates, affordable encoding-decoding complexity, and ease of reconfigurability support the growing development of M/T/Q/P-LC Flash memory devices, as well as lifecycle management as the characteristics of these devices change with time.

READ FULL TEXT
research
07/08/2019

Asymmetric LOCO Codes: Constrained Codes for Flash Memories

In data storage and data transmission, certain patterns are more likely ...
research
10/21/2020

The Secret Arithmetic of Patterns: A General Method for Designing Constrained Codes Based on Lexicographic Indexing

Constrained codes are used to prevent errors from occurring in various d...
research
11/14/2021

Read-and-Run Constrained Coding for Modern Flash Devices

The pivotal storage density win achieved by solid-state devices over mag...
research
02/28/2019

LOCO Codes: Lexicographically-Ordered Constrained Codes

Line codes make it possible to mitigate interference, to prevent short p...
research
02/03/2023

Efficient Constrained Codes That Enable Page Separation in Modern Flash Memories

The pivotal storage density win achieved by solid-state devices over mag...
research
10/10/2020

Power Spectra of Constrained Codes with Level-Based Signaling: Overcoming Finite-Length Challenges

Constrained codes are used to eliminate error-prone patterns in various ...
research
07/10/2020

On the Performance of Direct Shaping Codes

In this work, we study a recently proposed direct shaping code for flash...

Please sign up or login with your details

Forgot password? Click here to reset