Entropy Source Characterization via Allan Variance
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Solution Overview
Problem
Existing methods for characterizing the entropy source based on the jitter of a ring oscillator in electronic circuits face challenges such as the contribution of frequency dividers to noise being unknown, significant additional surface area required for characterization circuits, and low precision due to uncontrolled frequency ratios.
Innovation Solution
An electronic device comprising a first and second identical ring oscillators, a synchronous flip-flop, a counter, and circuits to modify the oscillators' periods and characterize the Allan variance, allowing for embedded characterization of the entropy source with controlled frequency ratios and reduced surface area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a frequency divider is used to obtain the Q factor for measuring oscillator oscillations, then the measurement can be implemented, but the contribution of the frequency divider circuit to the final noise is unknown and adds uncertainty to the entropy source characterization
Solution Approach 1:
The patent removes the frequency divider from the measurement system and directly counts oscillator periods using a counter circuit. This extraction eliminates the harmful noise contribution from the frequency divider while preserving the ability to measure the number of oscillations and calculate Allan variance for jitter characterization.
Solution Approach 2:
The patent introduces a counter circuit as an intermediary between the oscillators and the measurement system. This counter directly counts the number of periods of the first oscillator during Q periods of the second oscillator without using a frequency divider, thereby avoiding the noise contribution while enabling precise measurement of the oscillation ratio.
2Measurement precision
If separate characterization circuits are added next to the entropy source processing, then the jitter can be characterized, but significant additional surface area is required
Solution Approach 1:
The patent merges the entropy source generation function with the characterization function into a single integrated circuit. The same two oscillators and counter used for random number generation are also used for jitter characterization, eliminating the need for separate characterization circuits and reducing the total surface area required.
Solution Approach 2:
The oscillators and counter circuit serve dual purposes: they generate entropy for random number generation and simultaneously enable jitter characterization through Allan variance calculation. This multi-functionality eliminates redundant components and reduces the overall circuit footprint while maintaining both generation and characterization capabilities.
3Ease of manufacture
If uncontrolled frequency ratios are used between oscillators, then the measurement implementation is simplified, but the precision of jitter characterization is reduced
Solution Approach 1:
The patent uses feedback to control the frequency ratio between the two oscillators. The counter measures the actual ratio of oscillations, and this information is used to adjust the oscillators to maintain a predetermined rational frequency ratio, thereby ensuring precise jitter characterization while keeping the implementation straightforward.
Solution Approach 2:
The patent changes the frequency ratio parameter of the oscillators from uncontrolled to controlled values. By adjusting the oscillators to maintain a predetermined rational frequency ratio based on measured values, the system achieves both ease of manufacture and high measurement precision in the jitter characterization.
Data Source
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AI summary
This description relates to a device (1) comprising: a first oscillator (RO1) and a second oscillator (RO2) identical to the first; a flip-flop (FF) providing an output signal (S3) corresponding to a sampling of an output (S1) of the first oscillator (RO1) at a frequency of the second oscillator (RO2); a counter (COUNTER) providing a value (N) equal to a number of periods of the second oscillator (RO2) counted during each period of the output signal (S3) of the flip-flop (FF); a first circuit (FB CTRL) modifying a period of one of the oscillators (RO1, RO2) on the basis of the values (N) of the counter (COUNTER) so that an average deviation between the periods of the oscillators is equal to a target deviation; and a second circuit (PROCESS) characterizing an Allan variance on the output (O) of the counter from said values (N).