Leakage-Based Ring Oscillator Temperature Sensing With Low Complexity
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Solution Overview
Problem
Existing temperature sensors for on-chip heat management face challenges such as high design complexity, large area occupation, high power consumption, and susceptibility to external interference, particularly in advanced CMOS process nodes with complex integrated circuit chips.
Innovation Solution
A temperature sensor circuit utilizing a NAND gate and K delay units with leakage-based inverters and Schmitt triggers, forming a ring oscillator structure, which operates in PMOS and NMOS leakage modes, allowing for accurate temperature measurement with reduced control signal lines and low power consumption, and enhanced anti-interference capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional temperature sensor designs are used, then temperature measurement function is achieved, but design complexity increases and chip area occupation increases
Solution Approach 1:
The patent changes the operating parameter from voltage-mode to frequency-mode measurement. The ring oscillator's oscillation frequency is used as the measurement parameter, which has a direct exponential relationship with temperature through MOS transistor leakage current. This parameter change simplifies the overall design while maintaining measurement accuracy.
Solution Approach 2:
The patent extracts and utilizes the inherent leakage current characteristic of MOS transistors, which is typically considered a harmful effect, and converts it into the basis for temperature sensing. By taking out this parasitic effect and making it the core measurement mechanism, the design achieves simplicity while maintaining accuracy.
2Measurement precision
If traditional temperature sensor designs are used, then temperature measurement function is achieved, but chip area occupation increases
Solution Approach 1:
By changing to frequency-based measurement using ring oscillator, the patent reduces the required chip area. Frequency measurement can be achieved with simple counter circuits that occupy minimal area compared to traditional voltage measurement circuits requiring amplifiers, filters, and reference voltage generators.
Solution Approach 2:
The patent uses standard digital logic cells (NAND gates, inverters, Schmitt triggers) that are already present in CMOS process libraries. By copying and assembling these standard cells into a ring oscillator configuration, the design achieves area efficiency while maintaining measurement functionality.
3Measurement precision
If traditional temperature sensor designs are used, then temperature measurement function is achieved, but power consumption increases
Solution Approach 1:
The patent employs periodic oscillation of the ring oscillator to perform temperature measurement. Instead of continuous operation, the oscillator runs periodically and the frequency is measured over a counting period. This periodic action significantly reduces average power consumption while maintaining measurement accuracy through frequency measurement.
Solution Approach 2:
The ring oscillator is self-sustaining and does not require external reference voltage sources or complex biasing circuits. The oscillation is generated inherently by the odd number of inverters in the ring, and the frequency directly reflects temperature through leakage current variations, eliminating the need for additional power-consuming reference circuits.
4Measurement precision
If traditional temperature sensor designs are used, then temperature measurement function is achieved, but susceptibility to external interference increases
Solution Approach 1:
The patent replaces voltage-based measurement (analog domain) with frequency-based measurement (digital domain). Frequency is a digital parameter that is inherently more robust against noise and interference. The use of digital logic elements (NAND gates, Schmitt triggers) further enhances immunity to external interference compared to analog circuits.
Solution Approach 2:
The ring oscillator provides inherent feedback through its closed-loop structure. The oscillation frequency is determined by the total delay around the loop, which is stabilized by the feedback mechanism. This feedback ensures that the measurement is self-regulating and less susceptible to external disturbances.
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
The proposed solution simplifies design complexity, reduces chip area, achieves high accuracy with low power consumption, and improves robustness against external interference, enabling reliable temperature measurement across a wide temperature range.
Implementation Method 1
the leakage current of MOS transistor is exponential relationship to temperature, and the leakage current is exponential relationship to output frequency in ring oscillator
Data Source
AI summary
A reconfigurable all-digital temperature sensor includes a NAND gate and several delay units, the NAND gate comprises two input terminals and an output terminal, one input terminal is used for external starting control signal; a plurality delay units are connected in series, the input end of the first delay unit is connected to the output terminal of the NAND gate, and the output end of the last delay unit is connected to another input terminal of the NAND gate, thereby forming a ring oscillator structure; each delay unit includes a leakage-based inverter and a Schmitt trigger, and the output end of the leakage-based inverter is connected to the input end of the Schmitt trigger. The reconfigurable all-digital temperature sensor can realize the conversion of temperature-leakage-frequency based on the ring oscillator structure in the temperature range of −40˜125° C., thereby reducing the design complexity and achieving high accuracy.