Transistor PUF Cell Layout for Persistent Random IoT Keys
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Solution Overview
Problem
Implementing a Physical Unclonable Function (PUF) apparatus that generates a persistent, random number with equal probability for each output, while being low-cost in terms of power consumption and area, and suitable for integration in Internet of Things (IoT) devices, poses challenges due to the need for equal probability of output values and efficient manufacturing variations.
Innovation Solution
A PUF apparatus comprising a plurality of PUF cells with matched pairs of transistors of the same type, where the on-state characteristics are compared to determine a transistor difference value, generating a persistent random number based on random manufacturing variations, and using these cells for both selection and determination mechanisms to reduce size and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If matched pairs of transistors are used to generate random output based on manufacturing variations, then randomness and persistence of output are improved, but device area and power consumption increase
Solution Approach 1:
The patent combines the selection mechanism and determination mechanism into a single integrated structure where matched pairs of transistors serve both purposes. Each transistor pair simultaneously selects a PUF cell and determines the output bit, eliminating the need for separate selection circuits and reducing overall device area while maintaining output persistence.
Solution Approach 2:
The matched pair of transistors performs multiple functions: they act as the PUF element generating randomness from manufacturing variations, serve as the selection mechanism for choosing PUF cells, and function as the determination mechanism for generating output bits. This multi-functionality reduces the number of components needed and minimizes device area.
2Reliability
If multiple PUF cells are used to ensure equal probability output values, then output randomness is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent merges the selection and determination functions into a unified transistor pair structure, reducing device complexity. By using the same matched transistor pair for both selecting the PUF cell and determining the output bit, the system achieves equal probability output values without requiring separate complex selection circuits and determination logic.
3Ease of operation
If separate selection and determination mechanisms are used, then functional clarity is improved, but device area and power consumption increase
Solution Approach 1:
The patent combines selection and determination mechanisms into a single operational step using matched transistor pairs. This integration reduces power consumption by eliminating redundant circuit operations while maintaining functional clarity through the inherent differential comparison mechanism that clearly distinguishes between selected and non-selected states.
Data Source
AI summary
The present disclosure relates to a PUF apparatus and method for generating a persistent, random number. The generated number is random in that each particular instance of PUF apparatus should generate a randomly different number to all other instances of PUF apparatus, and is persistent in that each particular instance of the PUF apparatus should repeatedly generate the same number, within acceptable error correction tolerances. The persistent, random number is determined by selecting one or more PUF cells, each comprising a matched pair of transistors that are of identical design, and comparing an on-state characteristic of the pair (e.g., turn-on threshold voltage or gate-source voltage). The difference in on-state characteristic of each selected pair of transistors is caused by random manufacturing differences between the transistors. This causes the randomness between each different instance of PUF apparatus, and should be relatively stable over time to provide persistence of the generated number.