Leakage-Mode Ring Oscillator for IC Temperature Monitoring
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Solution Overview
Problem
Existing integrated circuit monitoring systems face inefficiencies due to complex relationships between oscillation frequency and temperature, and the need for accurate, context-specific MOSFET parameter monitoring, which is hindered by local variations and systematic effects, requiring a small, low-power monitoring circuit for embedded MOSFETs and silicon acceptance testing.
Innovation Solution
A ring oscillator with inverting stages where at least one transistor operates in a leakage mode, controlling oscillation frequency by limiting current flow, allowing for monitoring of operating parameters such as leakage current and temperature through predictable current leakage variations, using a gate voltage supply to manage current leakage and determine threshold voltages for low power modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a ring oscillator is used to monitor operating temperature, then temperature monitoring capability is provided, but the relationship between oscillation frequency and temperature becomes complex and requires complicated biasing circuits and/or analogue outputs
Solution Approach 1:
The patent changes the operating parameter of the transistor from standard conduction modes to leakage mode (subthreshold region). By operating the transistor in leakage mode, the oscillation frequency becomes exponentially dependent on temperature through the leakage current, providing a simplified and more predictable temperature monitoring mechanism without complex biasing circuits or analogue outputs.
2Productivity
If process geometries are reduced to increase integration density, then manufacturing capability is improved, but local variation of MOSFET characteristics becomes so large that simple chip-level guard-banded designs become heavily over designed and inefficient
Solution Approach 1:
The patent replaces traditional mechanical/guard-banded design approaches with an electrical monitoring system. By using a ring oscillator with transistors operating in leakage mode, the system electrically measures and monitors MOSFET characteristics in-situ, allowing for precise detection of local variations without relying on conservative guard-banding that leads to over-design.
Solution Approach 2:
The monitoring circuit uses transistors from the actual circuit being monitored (or identical transistors located nearby), allowing the system to self-characterize its own components. This self-service approach enables accurate measurement of local MOSFET variations without requiring external characterization equipment or conservative design margins.
3Ease of manufacture
If wafer acceptance test MOSFET parameters are used for monitoring, then manufacturing testing is simplified, but accuracy is reduced due to context-dependent effects and local variations that cannot be monitored from distant areas
Solution Approach 1:
The patent implements monitoring at the local circuit level rather than relying on distant wafer-level measurements. By placing ring oscillators with leakage-mode transistors directly within or near the circuit under test, the system captures local MOSFET characteristics including context-dependent effects such as stress engineering and implant shadowing, providing accurate in-situ monitoring that reflects actual operating conditions.
4Reliability
If a monitoring circuit is designed to monitor embedded MOSFET parameters, then manufacturing and adaptive circuit capabilities are improved, but the monitoring circuit itself consumes power and occupies area
Solution Approach 1:
The patent uses transistors operating in leakage mode where the subthreshold conduction current is exponentially sensitive to temperature and other parameters. This parameter change enables the monitoring circuit to achieve high sensitivity with minimal current consumption, as the leakage currents themselves serve as the monitoring signal rather than requiring additional active biasing currents.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables a compact, low-power monitoring circuit capable of accurately monitoring various integrated circuit parameters, including leakage current and temperature, with improved sensitivity and reduced power wastage, while providing precise control over leakage currents and temperature calibration.
Implementation Method 1
operating at least one of said inverting stages such that at least one transistor supplying current to said inverting stage limits current flow in and output signal slew rate of said inverting stage and thereby controls said oscillation frequency; and supplying a gate voltage to said transistor to operate said transistor in a leakage mode in which substantially all current flow through said transistor is by current leakage
Implementation Method 2
generating an oscillating signal at an oscillation frequency with a ring oscillator comprising a plurality of serially connected inverting stages
Data Source
AI summary
An integrated circuit 2 is provided with one or more monitoring circuits 14, 16, 18, 20 in the form of ring oscillators 22. These ring oscillators 22 include a plurality of tri-state inverters 24, 26, 28 containing a current-limiting transistor 42 operating in a leakage mode. The leakage current through the transistor 42 is dependent upon an operating parameter of the integrated circuit 2 being monitored. Accordingly, the oscillation frequency Fosc of the ring oscillator 22 varies in dependence upon the operating parameter to be measured.