Subthreshold Ring Oscillator Temperature Sensing Without ADCs
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Solution Overview
Problem
Conventional temperature sensors in integrated circuits, such as those using bandgap reference circuits (BGREF), face challenges due to large size and high power consumption, especially in advanced CMOS process nodes, and require precision analog-to-digital converters (ADCs), while ring oscillator sensors are sensitive to supply voltage rather than temperature and also consume significant resources.
Innovation Solution
A ring oscillator-based temperature sensor operating in subthreshold mode replaces BJTs and ADCs, producing a temperature-dependent frequency that is proportional to absolute temperature, eliminating the need for BJTs and ADCs, and utilizing the system clock for frequency measurement, thus reducing area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bandgap reference circuits (BGREF) with BJT sensing elements are used for temperature sensing, then temperature measurement capability is achieved, but circuit area becomes very large and power consumption increases significantly
Solution Approach 1:
The patent changes the operating parameters by using subthreshold MOS transistors instead of BJT sensing elements, and operating the ring oscillator in subthreshold mode. This parameter change enables temperature sensing functionality while dramatically reducing circuit area, as subthreshold MOS devices occupy significantly less area than BJT structures in advanced CMOS processes.
Solution Approach 2:
The patent substitutes the BJT-based sensing mechanism with a MOS-based ring oscillator system. By replacing the BJT sensing elements with MOS transistors operating in subthreshold region, the system achieves temperature sensing capability with reduced area and power consumption while maintaining measurement functionality.
2Measurement precision
If bandgap reference circuits (BGREF) with BJT sensing elements are used for temperature sensing, then temperature measurement capability is achieved, but power consumption becomes very high
Solution Approach 1:
The patent changes the operating parameters by using subthreshold MOS transistors instead of BJT sensing elements, and operating the ring oscillator in subthreshold mode. This parameter change enables temperature sensing functionality while dramatically reducing circuit area, as subthreshold MOS devices occupy significantly less area than BJT structures in advanced CMOS processes.
Solution Approach 2:
The patent substitutes the BJT-based sensing mechanism with a MOS-based ring oscillator system. By replacing the BJT sensing elements with MOS transistors operating in subthreshold region, the system achieves temperature sensing capability with reduced area and power consumption while maintaining measurement functionality.
3Measurement precision
If precision analog-to-digital converters (ADC) are used in temperature sensors, then measurement precision is improved, but area and power consumption increase significantly
Solution Approach 1:
The patent extracts and eliminates the precision ADC component from the temperature sensor system. By using a ring oscillator whose frequency naturally varies with temperature, the system converts temperature directly to a frequency signal that can be measured by simple digital counters, completely removing the need for precision ADC hardware and its associated area and power requirements.
Solution Approach 2:
The patent substitutes the ADC-based conversion mechanism with a direct frequency-based measurement system. The ring oscillator converts temperature to frequency, and digital counters measure the frequency, replacing the complex ADC conversion process with simpler digital counting operations that consume less area and power.
4Area of stationary object
If conventional ring oscillator sensors are used for temperature sensing, then area and power consumption are reduced, but sensitivity to supply voltage increases making them less accurate for temperature measurement
Solution Approach 1:
The patent implements feedback mechanisms through differential ring oscillator configurations and temperature compensation techniques. By using matched pairs of oscillators and comparing their frequency differences, or by incorporating temperature compensation circuits that adjust for supply voltage variations, the system achieves supply voltage insensitivity while maintaining temperature sensing accuracy.
Solution Approach 2:
The patent changes the operating parameters by using subthreshold MOS transistors instead of BJT sensing elements, and operating the ring oscillator in subthreshold mode. This parameter change enables temperature sensing functionality while dramatically reducing circuit area, as subthreshold MOS devices occupy significantly less area than BJT structures in advanced CMOS processes.
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 solution results in a smaller, more energy-efficient temperature sensor that is less sensitive to supply voltage, achieving significant savings in area and energy consumption while maintaining high precision, outperforming prior art in terms of energy efficiency and area usage.
Implementation Method 1
the ring oscillator has similar equations to a subthreshold MOS and can produce a temperature dependent frequency
Data Source
AI summary
A sensor circuit includes at least one ring oscillator having a supply port supplied by at least one current source and a reference frequency. A comparator compares a frequency output of the at least one ring oscillator with the reference frequency to yield a measurement, such as a temperature measurement.