Random number generator using ring oscillators with initial delay
Inventors
Assignees
United States Department of the Air Force
Publication Number
US-9361066-B2
Publication Date
2016-06-07
Expiration Date
2034-01-09
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Abstract
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.
Core Innovation
The invention is an apparatus and method for a ring oscillator based random number generator that utilizes intentional startup delays timed for each ring oscillator to uniformly spread the ring oscillator transition edges. This is achieved by adding a controlled incremental delay in the startup of each individual ring within the ring oscillator random number generator, using delay units typically found in the ring oscillators themselves to create coarse and fine delays of the enable signals.
The problem the invention addresses is that prior art ring oscillator random number generators rely on unintentional manufacturing variations to create phase differences between ring oscillators. Without sufficient difference, simultaneously starting all ring oscillators can lead to predictable output sequences with consistent zeros or ones for some time, reducing randomness. The invention solves this by intentionally staggering the startup times of ring oscillators, spreading out the transition edges over an oscillation cycle to ensure unpredictability in the random number output.
Claims Coverage
The patent includes multiple independent claims detailing apparatus and method features for a random number generator utilizing ring oscillators with staggered startup delays.
Incrementally staggered startup delays uniformly spread across the oscillation period
The random number generator includes a plurality of ring oscillator chains each with the same oscillation period, where their enable inputs receive incrementally staggered startup delays distributed uniformly across the oscillation period via a plurality of delay cells connected between an enable signal and each ring oscillator input.
Use of delay cells to induce different time delays in enable signals
The plurality of delay cells induce relatively different time delays in the enable signal to each of the plurality of ring oscillator chains, ensuring the staggered startup.
Ring oscillator output latching and exclusive OR processing
Each ring oscillator output is latched individually, and pairs of latched outputs are processed through a first plurality of exclusive OR gates, with outputs further combined through a second plurality of exclusive OR gates, eventually producing a single output representing the random bit.
Method for generating random numbers using staggered enable signal delays
The method includes latching outputs of N ring oscillators, performing successive exclusive OR operations on latched outputs, creating incrementally staggered time delay paths via time delay cells prior to each enable input, and applying an enable signal staggered uniformly across the oscillation period to generate randomness.
The claims collectively cover both apparatus and method aspects of a ring oscillator based random number generator with enabling signals staggered in time by delay cells to ensure uniformly spaced startup delays across the oscillation period, combined with latch and XOR circuitry for random number output generation.
Stated Advantages
Intentional staggering of ring oscillator startup times ensures truly random bits even when oscillators are very similar, overcoming prior art limitations relying on manufacturing variation.
Spreading oscillator transition edges evenly over the oscillation cycle improves unpredictability of the captured outputs.
Documented Applications
Generating random numbers in digital integrated circuits using ring oscillator based random number generators with improved randomness properties by controlled startup delay staggering.
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