CMOS Temperature Sensor with Modulated Sampling Frequency
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Solution Overview
Problem
Bipolar-based temperature sensors face challenges in integrating into digital circuits due to power supply noise, area requirements, and reduced accuracy, especially with the scaling down of semiconductor devices, as they require larger power supply rails and more area compared to CMOS-based sensors.
Innovation Solution
A CMOS-based temperature sensor with full band power supply rejection (PSR) is developed, incorporating a CMOS-based reference voltage generator, a temperature front-end circuit with a constant bias current, and a phase-rotated sigma-delta ADC that uses a low voltage digital power supply and modulates the sampling frequency to filter out power supply noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If bipolar-based temperature sensors are used, then temperature measurement capability is achieved, but power supply noise affects accuracy and larger area is required
Solution Approach 1:
The patent converts the harmful power supply noise into a beneficial filtering mechanism by using the noise itself as the modulation signal. The modulator mixes the temperature signal with the power supply noise frequency, and the notch filter selectively removes the noise frequency while preserving the temperature measurement signal, thereby turning the harmful noise into a reference for filtering.
Solution Approach 2:
The patent introduces an intermediary modulator and notch filter between the temperature sensor and the output. The modulator acts as an intermediary that shifts the temperature signal to a different frequency domain, and the notch filter serves as an intermediary that selectively removes power supply noise without affecting the temperature signal, thus mediating the harmful interaction between power supply noise and measurement accuracy.
2Measurement precision
If bipolar-based temperature sensors are used, then temperature measurement is achieved, but larger device area is required compared to CMOS-based sensors
Solution Approach 1:
The patent substitutes the bipolar-based temperature sensing mechanism with a CMOS-based mechanism. Instead of using bipolar transistors which require larger area, the invention uses CMOS transistors with a different operating principle (utilizing threshold voltage variations with temperature), achieving the same temperature measurement capability with significantly reduced device area.
3Measurement precision
If bipolar-based temperature sensors are used, then temperature sensing is achieved, but integration into digital circuits is difficult due to power supply requirements
Solution Approach 1:
The patent changes the power supply parameter from the bipolar requirement (larger voltage rails) to CMOS compatibility (standard digital circuit voltage levels). The CMOS-based temperature sensor operates from the same power supply as digital circuits, enabling seamless integration without requiring separate power supply infrastructure, thus improving adaptability to digital circuit environments.
Data Source
AI summary
The present disclosure describes embodiments of a temperature sensor with full band PSR. The temperature sensor can include a reference voltage generator, a temperature circuit, and an analog-to-digital converter (ADC). The reference voltage generator is configured to generate a reference voltage. The temperature circuit is configured to operate under a substantially constant bias current and to generate a temperature signal proportional to temperature. The ADC is electrically coupled to the reference voltage generator and the temperature circuit and configured to convert the temperature signal to a digital representation based on a sampling frequency. The ADC comprises a frequency generator configured to generate a modulation frequency having a random variation. The sampling frequency is modulated by the modulation frequency.