1.5-T Flash Memory PUF Random Number Generation
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Solution Overview
Problem
Physically unclonable function (PUF) circuitry faces challenges in generating high-quality random numbers due to systematic bias in memory cell states, which affects the randomness and reliability of the numbers produced, particularly in regions with manufacturing variations.
Innovation Solution
Incorporating whitening circuitry that resets and cycles memory cells to achieve a balanced distribution of bit states, using flash memory that is resistant to stress-induced leakage current and other aging defects, and implementing whitening algorithms to ensure approximately half of the random number bits are in each state, thereby enhancing randomness as quantified by NIST tests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If memory cells are used to generate random numbers directly, then the generation process is simple, but systematic bias in certain regions reduces the quality of randomness
Solution Approach 1:
A whitening circuit is introduced as an intermediary component between the memory cells and the random number output. This circuit processes the biased random bits from memory cells through XOR operations and shifting to produce unbiased random numbers, thereby resolving the contradiction between simple generation and high-quality randomness.
Solution Approach 2:
The patent transforms the parameter distribution of random bits by applying whitening algorithms that change the statistical parameters. The process adjusts the bias parameter from non-uniform distribution to uniform distribution (0.5 probability for each bit state), improving randomness quality without significantly increasing system complexity.
2Reliability
If whitening circuitry is added to reduce bias, then the quality of randomness improves, but the device complexity increases
Solution Approach 1:
The whitening circuit serves as a compact intermediary that achieves significant randomness improvement with minimal additional complexity. By using simple XOR gates and shift registers to process memory cell outputs, the circuit adds little complexity while substantially improving the statistical quality of generated random numbers.
Solution Approach 2:
The whitening algorithm efficiently changes the statistical parameters of the random bit stream through mathematical transformations. This approach achieves unbiased output (parameter transformation from biased to uniform distribution) with computationally simple operations, minimizing the complexity-quality trade-off.
3Ease of manufacture
If conventional memory is used, then the device is easier to manufacture, but stress-induced leakage current and aging defects reduce reliability
Solution Approach 1:
The patent employs flash memory technology which combines specific material properties (floating gate structure, oxide layers) to create a composite memory cell that is inherently resistant to SILC and aging defects. This composite structure maintains manufacturing compatibility while providing superior reliability for random number generation.
Solution Approach 2:
The patent uses flash memory cells that can be easily manufactured and replaced, leveraging their robustness against aging. The memory cells are designed to be disposable or replaceable units that maintain their random number generation capability over extended periods without degradation from SILC or other aging effects.
Data Source
AI summary
This disclosure relates generally to physically unclonable function (PUF) circuitry along with methods of generating numbers. In one embodiment, the PUF circuitry includes a memory, a memory control circuitry, and whitening circuitry. To reduce or eliminate the systematic bias from the array, whitening circuitry is configured to generate a random number comprising random number bits in response to the memory control circuit implementing at least one sequence of memory cycles on the array of the memory cells in the memory. The whitening circuitry is configured to provide the random number bits of the random number based on the variable bit states stored by the array of the memory cells. On average the whitening circuitry is configured to provide approximately half of the random number bits in the first bit state and half of random number bits in a second bit state.