Diode-Connected Inverter Ring Oscillator for Linear Temperature Sensing
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Solution Overview
Problem
Conventional thermal sensors, whether BJT-based, diode-based, or resistor-based, are either too large for small digital circuits or have poor output linearity and low temperature sensitivity, while digital thermal sensors like ring oscillators lack the necessary sensitivity for accurate temperature monitoring.
Innovation Solution
The design incorporates diode-connected transistors, specifically PMOS and NMOS transistors, in an inverter and ring oscillator configuration, where the propagation delay time is a linear function of temperature, enabling accurate temperature monitoring through output frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermal sensors (BJT-based, diode-based, or resistor-based) are used, then temperature sensitivity is high, but device size becomes large and output linearity deteriorates
Solution Approach 1:
The patent replaces conventional BJT-based, diode-based, or resistor-based thermal sensors with a digital ring oscillator circuit implemented in standard CMOS technology. This substitution transitions from analog sensing components to a digital logic-based system that achieves temperature sensing through propagation delay measurements, significantly reducing device area while maintaining or improving temperature sensitivity
Solution Approach 2:
The patent exploits the temperature-dependent behavior of CMOS transistor threshold voltages and carrier mobilities to create a ring oscillator whose propagation delay varies linearly with temperature. By carefully selecting and configuring the inverter stages with specific transistor aspect ratios and threshold voltages, the circuit transforms physical temperature changes into measurable digital timing variations, achieving high temperature sensitivity in a compact digital format
2Area of stationary object
If digital thermal sensors like conventional ring oscillators are used, then device size is small, but temperature sensitivity and output linearity deteriorate
Solution Approach 1:
The patent introduces diode-connected transistors at specific locations within the ring oscillator circuit to create localized regions with enhanced temperature sensitivity. These diode-connected devices are strategically placed to provide local feedback that linearizes the overall propagation delay versus temperature relationship, thereby improving global temperature sensitivity and linearity without significantly increasing the total device area
Solution Approach 2:
The patent implements feedback mechanisms using diode-connected transistors that sense local voltage changes due to temperature variations and feed this information back into the oscillator circuit. This feedback action compensates for non-linearities in the transistor characteristics and enhances the overall temperature sensitivity, allowing the compact digital circuit to achieve measurement precision comparable to or exceeding conventional analog thermal sensors
Data Source
Figure 1~2A
Figure 2B~2C
Figure 3
AI summary
The invention provides an inverter. The inverter includes a first converter and a second converter. The first converter is coupled between a supply voltage and an output node of the inverter. The second converter is coupled between the output node of the inverter and a ground voltage. The first converter, the second converter, or both include diode-connected transistors. The propagation delay time of the inverter is substantially a linear function of the temperature of the inverter.