PUF Circuit Isolation for Stable Transistor-Variation Sensing
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Solution Overview
Problem
Physically Unclonable Function (PUF) circuits in integrated circuits face instability due to variations in transistor characteristics such as NBTI, PBTI, and thermal noise, leading to inconsistent functionality over time and between identical circuits.
Innovation Solution
A stability-enhanced PUF circuit design that includes precharge circuitry with transistors of one type and uses only transistors of a second type to produce signals during sensing, disabling the first type transistors to isolate their variations, thereby improving stability and uniqueness of the output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PUF circuit uses both P-type and N-type transistors to produce output signal, then the circuit can function with nominal transistor strength equality, but the output becomes unstable over time due to different aging characteristics and NBTI/PBTI effects
Solution Approach 1:
The patent extracts and isolates the problematic element by using only N-type transistors for the PUF function, removing P-type transistors from the critical signal path. This extraction eliminates the instability caused by mixing transistor types with different aging characteristics, while the precharge circuitry handles the initialization function separately.
Solution Approach 2:
The patent segments the circuit into distinct functional blocks: precharge circuitry (using P-type transistors) and PUF core circuitry (using only N-type transistors). This segmentation allows each block to be optimized independently, with the precharge block handling initialization and the PUF core block providing stable unique identification.
2Reliability
If PUF circuit relies on gate-threshold variations in both P-type and N-type transistors, then the circuit can operate under various conditions, but the functionality becomes inconsistent due to different responses to temperature and voltage changes
Solution Approach 1:
The patent extracts the P-type transistors from the PUF core functionality, removing the source of inconsistent responses to environmental changes. By using only N-type transistors in the critical path, the circuit achieves consistent functionality across temperature and voltage variations, as N-type transistors exhibit more uniform characteristics under these conditions.
3Reliability
If PUF circuit includes precharge circuitry with transistors of first type and circuitry with transistors of second type, then the stability is improved by isolating variations, but the device complexity increases
Solution Approach 1:
The patent segments the circuit into precharge circuitry and PUF core circuitry with distinct transistor type assignments. This segmentation, while adding structural complexity, provides clear functional separation that improves output stability by preventing interaction between differently-aged transistor types during the critical PUF measurement phase.
Data Source
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AI summary
A Physically Unclonable Function circuit may include precharge circuitry that precharges an output. The precharge circuitry may include transistors of a first type such as N-type or P-type. Circuitry having only transistors of a second, different type may be coupled to the output. The circuitry may produce a signal at the output based on variations between the transistors of the second type. The circuitry may include first and second circuits such as first and second transistors of the second type that are crosscoupled. While the circuitry is producing the signal at the output, the precharge circuitry or any transistors not of the second type may be disabled or electrically disconnected from the output. In this way, the stability over time of the Physically Unclonable Function circuit may be improved, because only variations associated with transistors of the second type may be used in producing the signal.