Stress-Enhanced Ring Oscillator Circuit for MOSFET Aging Sensing
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Solution Overview
Problem
Conventional methods for monitoring and compensating transistor aging in MOSFETs, such as CMOS ring oscillator circuits, have low sensing resolution and are invasive, making it difficult to accurately detect stress-based aging effects, which leads to inefficient dynamic power consumption and overcompensation.
Innovation Solution
A transistor aging monitor circuit with a reference ring oscillator and a stressed ring oscillator, where transistors in the stressed ring oscillator receive a negative gate-to-source voltage bias, and stress-enhanced inverter circuits amplify aging effects to increase detection sensitivity, allowing for more precise compensation of performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CMOS ring oscillator circuits are used to monitor transistor aging, then the monitoring method is low-cost and reliable, but the sensing resolution is low (5%-10% frequency degradation range) and measurement precision is insufficient
Solution Approach 1:
The circuit is segmented into two separate ring oscillators: a stressed ring oscillator that experiences BTI/HCI aging effects and a reference ring oscillator that is protected from stress. This segmentation allows independent optimization of each oscillator's function, enabling high-precision aging detection without requiring complex single-circuit designs.
Solution Approach 2:
A dedicated frequency comparison circuit serves as an intermediary that compares the frequencies of the stressed and reference ring oscillators. This intermediary component translates the subtle frequency differences caused by aging into measurable signals, achieving high sensing resolution without directly modifying the oscillator circuits themselves.
2Productivity
If conventional ring oscillator implementations are used, then the circuit structure is simple, but the measurement time is long and productivity is reduced
Solution Approach 1:
The reference ring oscillator is prepared in advance and protected from stress throughout operation, so that when aging measurement is needed, the comparison can be made immediately without requiring lengthy measurement periods. The stressed oscillator continuously experiences aging conditions, accumulating measurable effects over time while the reference remains stable.
Solution Approach 2:
The stressed ring oscillator continuously operates under stress conditions during normal circuit operation, continuously accumulating aging effects. This continuous useful action allows aging to be monitored in real-time without interrupting normal circuit function or requiring separate measurement phases.
3Reliability
If conventional ring oscillator circuits are used, then the implementation is non-invasive, but the results are very sensitive to environmental variations such as temperature shifts
Solution Approach 1:
The frequency comparison circuit provides continuous feedback between the stressed and reference oscillators, allowing real-time compensation for environmental variations. When temperature or other environmental factors affect both oscillators similarly, the differential comparison automatically compensates, isolating the aging effect from environmental noise.
Solution Approach 2:
The reference ring oscillator is specifically designed with local quality differences from the stressed oscillator - it is protected from BTI/HCI stress through decoupling during monitoring mode. This local quality difference (stress vs. no-stress condition) allows the reference to serve as a stable baseline that is insensitive to aging, thereby improving overall measurement reliability.
4Measurement precision
If only PMOS devices in every other stage are stressed, then the circuit operation is simplified, but it is difficult to accurately measure the effects of stress-based aging
Solution Approach 1:
The stressed ring oscillator is designed as a copy of the reference ring oscillator in terms of topology and transistor types, but with the key difference that all transistors in the stressed oscillator are subjected to stress conditions. This copying approach ensures that both oscillators respond similarly to environmental variations, allowing accurate isolation of aging effects through comparison.
Data Source
AI summary
A stress-based aging monitor circuit includes a reference ring oscillator circuit and a stressed ring oscillator circuit that each include transistors like the transistors in a circuit to be monitored. Transistors in the stressed ring oscillator circuit receive a negative gate to source voltage bias while the reference ring oscillator is protected from stress. To measure performance degradation due to stress-based aging, the switching frequencies of the reference ring oscillator circuit and the stressed ring oscillator circuit are compared. The reference ring oscillator and the stressed ring oscillator include stress-enhanced inverter circuits configured to amplify stress-based aging effects to increase sensitivity to the performance degradation caused by stress-based aging. Increased sensitivity increases the precision (e.g., higher resolution) of a supply voltage guard band adjustment used to compensate for the performance degradation to reduce or avoid overcompensating for the effects of stress-based aging.