PUF Bit Cell Characterization Using Ring-Oscillator Noise Injection
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Solution Overview
Problem
There is a need to develop a method to quickly evaluate the stability of bit cells in a physically unclonable function (PUF) generator to mask unpredictable and filter out unstable bit cells, ensuring unique, unclonable, and reliable PUF signatures.
Innovation Solution
The PUF generator includes a PUF cell array with bit cells that are evaluated for stability by introducing noise through ring oscillators, allowing for the identification and filtering out of unstable bit cells to generate a stable PUF signature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noise is introduced to evaluate bit cell stability, then the reliability of PUF signature is improved, but the device complexity increases due to additional noise injection circuitry
Solution Approach 1:
The PUF generator uses its own intrinsic physical variations to generate noise signals through ring oscillators, eliminating the need for external noise sources. The system self-evaluates its bit cell stability by comparing responses under different operating conditions, using its inherent physical properties rather than requiring additional complex evaluation equipment.
Solution Approach 2:
The ring oscillator circuits serve multiple functions: they generate the PUF responses, introduce controlled noise for stability evaluation, and enable bit cell characterization. This multi-functionality reduces the need for separate dedicated noise injection equipment, thereby managing device complexity while improving reliability.
2Reliability
If multiple operating conditions are tested to filter unstable bit cells, then the PUF signature uniqueness is improved, but the loss of time increases due to extended evaluation period
Solution Approach 1:
The system performs preliminary characterization of bit cell stability during manufacturing or initial operation by testing under multiple operating conditions. Unstable bit cells are identified and filtered out in advance, creating a mask that is stored for future use. This preliminary action ensures that only stable bit cells are used in normal PUF operations, eliminating the need for repeated time-consuming evaluations while maintaining uniqueness.
3Measurement precision
If ring oscillators are used for noise injection, then the stability evaluation accuracy is improved, but the device complexity increases due to additional oscillator circuits
Solution Approach 1:
The ring oscillators exploit changes in operating parameters such as supply voltage and temperature to induce noise that reveals bit cell stability characteristics. By varying these parameters and observing response changes, the system achieves accurate stability evaluation without requiring complex measurement equipment, using only the inherent sensitivity of the oscillators to parameter variations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the rapid identification and filtering of unstable bit cells, resulting in a unique and reliable PUF signature that ensures secure communication and authentication.
Implementation Method 1
introducing noise through ring oscillators
Data Source
AI summary
Disclosed is a physical unclonable function generator circuit and method. In one embodiment, physical unclonable function (PUF) generator includes: a PUF cell array that comprises a plurality of bit cells, wherein each of the plurality of bit cells comprises at least two access transistors, at least one enable transistor, and at least two storage nodes, wherein the at least two storage nodes are pre-configured with substantially the same voltages allowing each of the plurality of bit cells having a first metastable logical state; a PUF control circuit coupled to the PUF cell array, wherein the PUF control circuit is configured to access the plurality of bit cells to determine second logical states by turning on the at least one enable transistor and turning off the at least two access transistors of each of the plurality of bit cells, and based on the second logical states of the plurality of bit cells, to generate a PUF output; and a noise injector coupled to the PUF control circuit and the PUF cell array, wherein the noise injector is configured to create stressed operation conditions to evaluate stability of the plurality of bit cells.