Capacitor Ratio PUF Circuit for Secure Chip Identification
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Solution Overview
Problem
Existing chip identifiers, such as electronic fuses, are susceptible to theft and misuse due to their ease of physical access, necessitating a more secure and unclonable identification method.
Innovation Solution
A capacitor ratio identification system utilizing an oscillator, digital controller, and capacitance measurement circuitry to determine the capacitance ratio of capacitors, which serves as a physically unclonable function (PUF) for chip identification, requiring specific analog measurement circuitry for access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electronic fuses are used as chip identifiers, then the identification method is simple and easy to access, but the security is compromised due to susceptibility to theft and misuse
Solution Approach 1:
The patent introduces an intermediary measurement circuit as a mediator between the identifier element (capacitor) and the external reader. This circuit is required to physically access and measure the capacitor's electrical characteristics, creating an intermediate layer that prevents direct access and copying, thus resolving the contradiction between ease of access and security.
Solution Approach 2:
The patent replaces the purely electronic/digital identification system (electronic fuses) with a system that requires analog electrical measurement. By substituting the identification mechanism from digital bit-reading to analog capacitor measurement, it introduces physical measurement requirements that are harder to replicate, thereby improving security while maintaining operational simplicity.
2Reliability
If capacitor ratio identification is implemented, then security is improved through physically unclonable functions, but device complexity increases due to additional measurement circuitry
Solution Approach 1:
The patent designs the measurement circuit to serve multiple functions: it can measure different capacitor ratios, support various identification schemes, and potentially perform other electrical characterizations. By making the circuit universal and multi-functional, the patent reduces the relative complexity burden, as the same circuit infrastructure serves multiple purposes rather than requiring separate dedicated circuits for each function.
Solution Approach 2:
The patent utilizes parameter changes in the capacitor (electrical characteristics such as capacitance ratio) as the basis for identification. By changing the identification parameter from digital fuse states to analog capacitor electrical properties, the system achieves higher security through physically unclonable characteristics while the measurement circuit remains relatively simple, thus managing the complexity-security tradeoff.
3Ease of manufacture
If traditional electronic fuses are used, then manufacturing is simple and cost-effective, but the identifiers are vulnerable to physical theft and replication
Solution Approach 1:
The patent converts the potential harm of physical access into a benefit by using the physical electrical characteristics of capacitors (which are inherently difficult to copy) as the identification basis. The very fact that capacitors have unique, physically determined electrical properties that can be measured but not easily replicated becomes the security feature, turning the vulnerability of physical access into an advantage for creating unclonable identifiers.
Solution Approach 2:
The patent changes the identification parameter from easily copied digital fuse states to physically determined capacitor electrical characteristics (capacitance ratio). This parameter change maintains manufacturing simplicity since capacitors are standard electronic components, but fundamentally improves security by using physical properties that are inherently difficult to replicate, thus resolving the contradiction between manufacturing ease and security against theft.
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 capacitance ratio provides a secure and stable chip identifier that is difficult to read or replicate, offering superior security compared to traditional electronic fuses.
Implementation Method 1
an oscillator including a first switch, a current source, a capacitor, and a comparator, the capacitor and the comparator coupled at a node
Implementation Method 2
one or more delay buffers coupled to the comparator
Data Source
AI summary
A system includes an oscillator comprising a first switch, a current source, a capacitor, and a comparator, the capacitor and the comparator coupled at a node. The system includes one or more delay buffers coupled to the comparator. The system includes a first inverter coupled to the one or more delay buffers. The system includes a first buffer coupled to the one or more delay buffers. The system includes a first coupling capacitor coupled to the first inverter and the first buffer via second and third switches, respectively. The system includes a second inverter coupled to the one or more delay buffers. The system includes a second buffer coupled to the one or more delay buffers. The system includes a second coupling capacitor coupled to the second inverter and the second buffer via fourth and fifth switches, respectively. The first and second coupling capacitors are coupled to the oscillator.