Dual-Oscillator Monitoring Circuit for Clock Failure Identification
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Solution Overview
Problem
Existing in-vehicle monitoring circuits fail to maintain operation and perform protective functions when an oscillator abnormally stops, particularly in systems requiring functional safety standards like ISO 26262, due to the reliance on clock signals from oscillators.
Innovation Solution
A monitoring circuit design utilizing multiple oscillators and frequency dividers with separate reference voltage sources, counters, and a selector to ensure continuous operation by switching to a normal-state clock signal upon abnormality detection, without requiring a charging and discharging circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single oscillator is used for clock signal generation, then the circuit structure is simple, but the system cannot maintain operation when the oscillator abnormally stops
Solution Approach 1:
The patent divides the clock signal generation system into multiple independent oscillators (first oscillator and second oscillator), each capable of operating independently. This segmentation allows the system to maintain functionality even when one oscillator fails, directly resolving the contradiction between reliability and complexity by distributing the critical function across separate components.
Solution Approach 2:
The patent implements preliminary action by pre-configuring multiple oscillators and establishing a switching mechanism before any abnormality occurs. The monitoring circuit continuously checks the operational state of each oscillator and is ready to switch to a backup oscillator immediately upon detecting a failure, ensuring continuous operation without requiring complex real-time decision-making during the abnormal event.
2Reliability
If multiple oscillators are used with separate reference voltage sources, then abnormality detection capability is enhanced, but the circuit scale increases
Solution Approach 1:
The patent segments the reference voltage generation into separate reference voltage sources for each oscillator, allowing independent monitoring and failure detection. This segmentation enables the system to detect abnormalities in one oscillator without affecting the other, enhancing reliability while keeping each oscillator module relatively simple and modular.
Solution Approach 2:
The patent introduces a monitoring circuit as an intermediary component that observes the operational state of multiple oscillators and reference voltage sources without being part of their core oscillation mechanism. This intermediary enables comprehensive abnormality detection while maintaining the independence and simplicity of each oscillator module, effectively managing the trade-off between detection capability and circuit scale.
3Measurement precision
If a charging and discharging circuit is added for abnormality detection, then the monitoring accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent applies self-service by enabling oscillators to monitor their own operational state through their inherent oscillation characteristics. The monitoring circuit detects abnormalities by observing whether oscillators are producing expected clock signals, allowing the system to achieve monitoring accuracy without adding complex external charging and discharging circuits to each oscillator module.
Data Source
AI summary
A monitoring circuit includes first and second oscillators, first and second frequency dividers, first and second counters, a determination portion, and an identification portion. The first and second frequency dividers respectively divide frequencies of first and second clock signals outputted from the first and second oscillators, respectively. The first and second counters respectively count the numbers of clocks of the second and first clock signals at first and second numbers of periods of first and second frequency-divided signals outputted from the first and second frequency dividers, respectively. The determination portion determines, based on results of counting by the first and second counters, whether or not an abnormality has occurred in either of the first and second clock signals. The identification portion identifies, at the occurrence of an abnormality in either of the first and second clock signals, which of the first and second clock signals is in an abnormal state.