Switched-Capacitor Temperature Sensor Circuit for Linear Low-Temp Sensing
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Solution Overview
Problem
Integrated temperature sensors on integrated circuits face issues with linearity deterioration at low temperatures, require multiple calibrations, and have high power consumption due to current application through resistors.
Innovation Solution
A temperature sensor circuit using switched capacitors with differential sensing circuits, comprising n-channel and p-channel metal-oxide-semiconductor transistors, and a voltage reference circuit for biasing, along with a controller for process control and analog-to-digital conversion, achieving linear temperature dependence and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistive temperature sensor with different material resistors is used, then temperature sensing capability is achieved, but linearity deteriorates for temperatures below 0°C and power consumption increases
Solution Approach 1:
The patent changes the fundamental operating parameter from resistive (current-based) to capacitive (voltage-based) sensing. The temperature sensor uses capacitors with temperature-dependent capacitance values rather than resistors with temperature-dependent resistance values. This parameter change enables linear temperature measurement across the full range including below 0°C while significantly reducing power consumption since capacitors can be charged and discharged without requiring continuous current flow through sensing elements.
Solution Approach 2:
The patent substitutes the resistive sensing mechanism with a capacitive sensing mechanism. Instead of using ohmic law-based resistive temperature detection that requires continuous current application, the invention uses voltage-to-frequency conversion through capacitive charging and discharging cycles. This substitution eliminates the need for continuous power application to sensing elements while maintaining measurement capability across all temperature ranges.
2Measurement precision
If a resistive temperature sensor is used, then temperature sensing is achieved, but multiple calibrations are required at different temperatures
Solution Approach 1:
The patent changes from resistive to capacitive parameter usage, where capacitor values inherently exhibit linear temperature dependence across the full operating range. This physical parameter change eliminates the need for multiple calibration points at different temperatures, as the capacitive sensing mechanism provides consistent linear response from -50°C to 120°C without requiring compensation for non-linear resistive behavior.
3Measurement precision
If current is applied through resistors in a resistive temperature sensor, then temperature measurement is enabled, but power consumption increases significantly
Solution Approach 1:
The patent replaces the resistive sensing system that requires continuous current application with a capacitive sensing system that uses voltage charging and discharging. The temperature-dependent capacitance values are exploited to create voltage changes that can be measured without continuous power application to the sensing elements, thereby significantly reducing the power consumption while maintaining temperature measurement capability.
Solution Approach 2:
The patent employs periodic charging and discharging cycles of capacitors to enable temperature measurement. Instead of continuous current flow through resistors, the system uses periodic voltage application to charge capacitors, then measures the discharge characteristics or voltage changes that reflect temperature. This periodic action reduces average power consumption while enabling continuous temperature sensing.
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 provides improved accuracy, linearity, and lower power consumption by ensuring a linear voltage dependence on temperature, allowing for precise temperature measurements with reduced energy use.
Implementation Method 1
a first capacitor (110) connected to a first reset transistor (120) for biasing the first capacitor (110) to a first bias voltage, a second capacitor (150) connected to a second reset transistor (160) for biasing the second capacitor (150) to a second bias voltage
Implementation Method 2
a bias transistor (140) having a first terminal connected to the first capacitor (110), a second terminal connected to the second capacitor (150), and a third terminal connected to a voltage readout node (103)
Data Source
Figure 1
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Figure 4
AI summary
A temperature sensor (300) comprising at least one temperature sensing circuit (100). Each temperature sensing circuit (100) comprise a series connection of a first connecting node (111), a first capacitor (110) connected to a first reset transistor (120) for biasing the first capacitor to a first bias voltage, a bias transistor (140) for distributing charges between the first and second capacitor after biasing the first and second capacitor, a second capacitor (150) connected to a second reset transistor (160) for biasing the second capacitor to a second bias voltage, a second connecting node (151). Each temperature sensing circuit comprises at least one voltage readout node between the first capacitor (110) and the second capacitor (150).