SRAM PUF Robustness via Differential Source Bias
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Solution Overview
Problem
Conventional SRAM-based physically unclonable functions (PUFs) face challenges in generating robust and unique device information due to manufacturing variations and environmental factors, making it difficult to predict and recreate the initial power-up states of SRAM cells.
Innovation Solution
The implementation of a differential source bias condition upon powering up SRAM cells, which modifies their natural state, allowing for multiple power-up states by applying different voltage settings between source lines, thereby increasing the robustness of the PUF response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SRAM is used with natural power-up states, then the PUF generates unique device information, but the robustness is insufficient and it is easier to extract unique information
Solution Approach 1:
The patent applies a differential source bias condition to the SRAM cells before the natural power-up process occurs. This preliminary action modifies the initial states of the SRAM cells, making the power-up behavior more predictable and robust while still maintaining uniqueness. The bias condition is applied during the power-up phase, influencing which state (0 or 1) each cell settles into, thereby enhancing the reliability of the PUF response.
Solution Approach 2:
The patent changes the electrical parameters of the SRAM cells by applying different voltage levels to the source lines (e.g., VSS + 0.1V to VSS + 0.5V). This parameter modification alters the natural power-up behavior of the cells, creating more stable and robust PUF responses. By varying the source bias voltage, the system can control the differential behavior of paired SRAM cells, improving the reliability of the generated unique information.
2Adaptability or versatility
If multiple voltage settings are applied to source lines, then multiple power-up states are achieved, but the device complexity increases
Solution Approach 1:
The patent divides the SRAM array into multiple banks, where each bank can be independently powered up with different differential source bias conditions. This segmentation allows the system to generate multiple challenge-response pairs by selectively activating different banks with different voltage settings, thereby achieving adaptability without requiring complex global control circuitry.
Solution Approach 2:
The differential source bias circuitry is designed to serve multiple functions: it can apply different voltage settings to different SRAM banks, it can be controlled through existing control signals (e.g., bank select signals), and it enhances the PUF's ability to generate multiple unique responses from the same physical structure. This multi-functionality reduces the need for additional dedicated circuitry.
Data Source
AI summary
A plurality of memory cells, in which each memory cell includes two corresponding supply terminal inputs, is powered up while applying a voltage differential between the corresponding supply terminal inputs for each of the plurality of memory cells. After powering up, the plurality of memory cells is read and a physically unclonable function (PUF) response is generated from data of the reading.