Resistor-Bridge PUF Cells for Stable Low-Bias Random Number Generation
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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 value, is low-cost in terms of power and area, and remains stable over time, while minimizing systematic bias and component influence.
Innovation Solution
A PUF apparatus comprising a plurality of PUF cells with a full resistor bridge or H-bridge configuration, where random manufacturing differences create a persistent random number based on the impedance difference between the two sides of the bridge, with a determination unit to select and read out PUF values from these cells, and a readout unit to convert analog signals to digital, using a voltage reference generator to maintain stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a PUF apparatus uses full resistor bridge configuration with random manufacturing differences, then randomness and persistence of generated numbers are improved, but systematic bias and component influence may worsen
Solution Approach 1:
The patent employs asymmetric resistor bridge configuration where the two sides of the bridge have deliberately different nominal resistance values. This asymmetry ensures that random manufacturing variations produce measurable differential voltages while the asymmetric design itself helps cancel out systematic biases through differential measurement techniques
Solution Approach 2:
The patent introduces intermediate calibration and measurement steps between the resistor bridge and final PUF value generation. A determination unit measures and compensates for systematic biases in the resistor values, using these measurements as intermediaries to correct the raw signals before generating the final persistent random number
2Use of energy by stationary object
If a PUF apparatus minimizes components to reduce power and area, then power consumption and area are reduced, but measurement precision and reliability may worsen
Solution Approach 1:
The patent combines multiple functions into the determination unit, which simultaneously performs bias measurement, compensation calculations, and PUF value generation. This functional integration reduces the need for separate calibration circuits and components, minimizing power consumption and area while maintaining measurement precision through software-based compensation algorithms
3Device complexity
If a PUF apparatus uses minimal components, then device complexity is reduced, but reliability and stability over time may worsen
Solution Approach 1:
The patent implements self-calibration and self-compensation mechanisms within the determination unit. The system automatically measures its own systematic biases and applies corrections without external intervention, maintaining reliability over time despite using minimal physical components. This self-service approach compensates for aging and environmental variations through software algorithms
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
The solution ensures a persistent random number with equal probability, reducing power consumption and area, while minimizing systematic bias and maintaining stability over time, suitable for applications like IoT device security.
Implementation Method 1
each PUF cell comprising a first potential divider comprising a first resistor and a second resistor connected to each other in series at a first measurement point; and a second potential divider, coupled in parallel to the first potential divider, and comprising a third resistor and a fourth resistor connected to each other in series at a second measurement point
Implementation Method 2
a first potential divider comprising a first resistor and a second resistor connected to each other in series at a first measurement point
Data Source
Figure 1
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Figure 4a
AI summary
A Physical Unclonable Function, PUF, apparatus is disclosed. The apparatus comprises a plurality of PUF cells that each comprise a first potential divider and a second potential divider. The apparatus also comprises a determination unit that comprises a selection unit for selecting at least one of the plurality of PUF cells, and a readout unit coupled to each selected PUF cell. The readout unit is configured to determine a PUF value for the selected PUF cell based on a difference between a first analog voltage at the first potential divider and a second analog voltage at the second potential divider.