Parallel Ring Oscillator Test Structure for Fast Oscillation Screening
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Solution Overview
Problem
Testing multiple ring oscillators used in high-definition content protection (HDCP) for secret key generation is costly and inefficient due to the asynchronous nature and large number of oscillators, making conventional testing methods impractical and costly.
Innovation Solution
A modular ring oscillator test structure that allows for parallel testing of multiple oscillators, reconfiguring them into a testable form for structural and functional testing, reducing test time and cost by integrating testing with other system logic and using control signals to validate oscillation frequency within specified jitter limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional functional testing methods are used for each ring oscillator individually, then testing accuracy is maintained, but test time and cost increase substantially with the number of oscillators
Solution Approach 1:
The patent combines multiple ring oscillators into a single integrated test structure where multiple oscillators are connected in parallel and tested simultaneously through a unified test interface. This merging approach allows functional testing of N oscillators to be performed in a single test cycle rather than requiring N separate test cycles, thereby maintaining testing accuracy while reducing test time proportionally to the number of oscillators tested in parallel.
Solution Approach 2:
The patent creates a universal test structure that can accommodate and test any number of ring oscillators through a single standardized interface. The test structure uses multiplexers and shared control logic to provide multi-functional capability, allowing the same test hardware to test one oscillator or many oscillators without requiring additional test equipment or interfaces for each individual oscillator.
2Reliability
If individual on-chip counters are used for each ring oscillator, then oscillation detection is achieved, but hardware overhead and test setup complexity increase with the number of oscillators
Solution Approach 1:
The patent merges multiple individual counter functions into a single shared counter resource that is time-multiplexed across multiple oscillators. Instead of having dedicated counters for each oscillator, the test structure uses a single counter controlled by multiplexers to count oscillations from different oscillators sequentially, thereby maintaining reliable oscillation detection while reducing hardware overhead from O(N) counters to O(1) counter.
Solution Approach 2:
The patent introduces multiplexers as intermediary components between the oscillators and the shared counter. These multiplexers act as mediators that selectively connect different oscillator outputs to the common counter based on control signals, enabling a single counter to serve multiple oscillators without direct one-to-one connections, thus reducing hardware complexity while maintaining detection reliability.
3Measurement precision
If direct observation of ring oscillator output at the tester is performed, then functional testing is possible, but test access efficiency is poor due to asynchronous nature of ring oscillators
Solution Approach 1:
The patent introduces synchronizers and clocking circuits as intermediary components between the asynchronous ring oscillators and the synchronous test equipment. These intermediaries convert the asynchronous oscillator outputs into synchronous signals that can be efficiently captured and processed by the test equipment, thereby maintaining functional testing capability while dramatically improving test access efficiency by enabling synchronized operation with the test system.
Solution Approach 2:
The patent implements feedback mechanisms where the test structure monitors the oscillation outputs and uses this information to control the testing process. The feedback allows the system to adapt to the actual oscillation states, enabling efficient test access by dynamically adjusting test parameters based on real-time oscillator behavior rather than attempting to force synchronous operation.
Data Source
AI summary
A method and apparatus is disclosed herein for testing of multiple ring oscillators. In one embodiment, the apparatus comprises at least one ring oscillator structure having a ring oscillator having an inverter chain with an odd number of inverters connected back-to-back and operable to produce an oscillatory output, and a test structure coupled to provide either an observability chain input or a test input to the ring oscillator and to receive the oscillatory output as a feedback from the ring oscillator.