Digital Double Sampling CMOS Temperature Sensor
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Solution Overview
Problem
Conventional CMOS temperature sensors rely on differential circuits, consuming more power and requiring larger circuit areas due to their operation in the analog domain, and face challenges with temperature-independent reference voltage generation due to variations in bipolar junction transistor saturation currents.
Innovation Solution
A CMOS temperature sensor utilizing single-ended circuits, where a PTAT buffer generates digital voltage signals across two nodes, amplified and converted by a single-ended A/D converter, and compared with a digitally generated reference voltage to produce a digital output signal, eliminating the need for differential signals and enabling easier calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If differential circuits are used in CMOS temperature sensors, then measurement precision is improved, but power consumption increases and circuit area increases
Solution Approach 1:
The patent replaces the analog differential circuit system with a digital measurement system. Specifically, it uses a digital-to-analog converter (DAC) to generate reference voltages and a successive approximation register (SAR) ADC to convert the measured voltage to digital form, eliminating the need for complex analog differential amplification circuits while maintaining measurement precision.
Solution Approach 2:
The patent changes the operating domain from analog to digital by introducing ADC and DAC components. The temperature measurement is converted to a digital value through the SAR ADC, and the reference voltage is generated digitally through the DAC, fundamentally changing how the measurement and reference signals are processed and compared.
2Measurement precision
If differential circuits are used in CMOS temperature sensors, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces the analog differential circuit system with a digital measurement system. Specifically, it uses a digital-to-analog converter (DAC) to generate reference voltages and a successive approximation register (SAR) ADC to convert the measured voltage to digital form, eliminating the need for complex analog differential amplification circuits while maintaining measurement precision.
3Power
If band gap reference circuit with BJTs is used, then reference voltage is generated, but temperature variation occurs due to saturation current spread
Solution Approach 1:
The patent employs a feedback mechanism where the digital output from the SAR ADC is converted back to analog form through the DAC and compared with the original measurement. This allows for calibration and correction of the reference voltage to compensate for temperature variations and BJT saturation current spread, improving the stability of the reference voltage over temperature.
4Measurement precision
If analog domain operation is used, then temperature signal is processed, but power consumption increases
Solution Approach 1:
The patent replaces the analog differential circuit system with a digital measurement system. Specifically, it uses a digital-to-analog converter (DAC) to generate reference voltages and a successive approximation register (SAR) ADC to convert the measured voltage to digital form, eliminating the need for complex analog differential amplification circuits while maintaining measurement precision.
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 reduces power consumption and circuit complexity while ensuring accurate temperature measurement by operating in the digital domain, mitigating temperature variations associated with bipolar junction transistors.
Implementation Method 1
PTAT buffers can generate a voltage signal of the base to emitter voltage (VBE) across a MOSFET within the PTAT buffer. By using MOSFETs with different bias to current densities, a voltage difference ΔVBE can be generated, representing the difference between two differential nodes of the PTAT buffer. This voltage signal is proportional to temperature.
Implementation Method 2
PTAT buffers can generate a voltage signal of the base to emitter voltage (VBE) across a MOSFET within the PTAT buffer. By using MOSFETs with different bias to current densities, a voltage difference ΔVBE can be generated, representing the difference between two differential nodes of the PTAT buffer. This voltage signal is proportional to temperature.
Data Source
AI summary
An on-chip temperature sensor for generating a digital output signal representing a temperature value includes: a proportional to absolute temperature (PTAT) buffer for alternately generating a first voltage signal representing a first temperature of the PTAT buffer and a second voltage signal representing a second temperature of the PTAT buffer; an analog to digital (A/D) converter, coupled to the PTAT buffer, for converting the first voltage signal to a first digital voltage signal and for converting the second voltage signal to a second digital voltage signal; and a digital output generating block, for receiving the first digital voltage signal and the second digital voltage signal, and comparing a difference between the first digital voltage signal and the second digital voltage signal with a digital voltage reference signal to generate the digital output signal.