Ring Oscillator Startup Delays for Unpredictable Random Bits
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Solution Overview
Problem
Prior art ring oscillator-based random number generators may produce predictable output streams due to similar startup phases of individual oscillators, leading to non-random bit generation.
Innovation Solution
Incorporating a delay circuit between each ring oscillator's enable signal and the next to intentionally stagger their startup across oscillation cycles, ensuring random bit generation by distributing transitioning edges evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ring oscillators are enabled simultaneously without delay, then the circuit operation is simple and fast, but the output may be predictable due to consistent initial states
Solution Approach 1:
The patent applies preliminary action by introducing delay circuits before the enable signals of ring oscillators. These delay circuits are configured to stagger the startup timing of each oscillator, ensuring that they do not all start simultaneously. This preliminary timing adjustment guarantees phase differences and random initial states before the oscillators begin operation, thereby improving output randomness without requiring complex post-processing.
2Reliability
If delay circuits are added to stagger oscillator startup, then randomness is improved, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the enable signal distribution into multiple staged groups. Instead of using individual delay circuits for each oscillator, the enable signal is segmented and distributed through a hierarchical structure where intermediate signals are generated and then broadcast to multiple oscillators. This segmented approach reduces the total number of delay circuits while maintaining the staggered startup pattern across all oscillators.
Solution Approach 2:
The patent applies merging by combining multiple delay circuit functions into shared intermediate signal generation. Multiple ring oscillators share common delay stages, where a single delay circuit's output serves as the enable signal for multiple oscillators. This merging of functions reduces the overall component count and circuit complexity while still achieving the desired staggered startup effect across all oscillators.
Data Source
AI summary
Apparatus and method for a ring oscillator based random number generator with intentional startup delays timed for each ring to provide a uniform initial spreading of the ring oscillator transition edges. This invention adds a controlled incremental delay in the startup of each individual ring within the ring oscillator random number generator. Typically the delay units used in the ring oscillators themselves can be used to get a course delay between the start times of each ring. A subset of the rings start up with a particular course delay and different fine delays such that the transition edges of all the rings are spread out over the oscillation period. This spreading of the transition edges ensures the output of the random number generator are not a predictable sequence of ones and zeros based on a simultaneous startup of all rings at the same time.