Capacitor-Referenced Temperature Sensing With Chopped Noise Rejection
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Solution Overview
Problem
Existing temperature sensors face challenges in achieving low noise performance with high sample rates, low integrated area, and low power operation, particularly in MEMS-based clock applications, where high accuracy and low Allan deviation are required.
Innovation Solution
The use of a switched capacitor network with a digital Sigma-Delta modulator, chopping circuitry, and a pseudo-differential VCO-based analog-to-digital converter to mitigate 1/f noise and circuit offsets, along with a feedback loop that adjusts the Sigma-Delta modulator input based on error data, effectively converts the temperature-dependent resistive element's analog error into a digital code.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional temperature sensing circuits are used, then temperature measurement can be achieved, but noise performance deteriorates at high sample rates
Solution Approach 1:
The patent employs periodic chopping action at a frequency significantly higher than the temperature signal bandwidth to modulate the temperature-dependent voltage, thereby moving the signal spectrum away from low-frequency noise and offset regions. This periodic modulation enables high-precision temperature measurement at high sample rates by eliminating the harmful 1/f noise and DC offsets that would otherwise degrade measurement accuracy.
Solution Approach 2:
The patent introduces an intermediary switched-capacitor network that acts as a noise-filtering mediator between the temperature-sensitive bipolar transistors and the measurement system. This intermediary structure, combined with periodic chopping, filters out low-frequency noise components while preserving the temperature signal, thereby improving noise performance without sacrificing measurement precision.
2Object-affected harmful factors
If noise filtering techniques are applied, then noise performance improves, but circuit complexity increases
Solution Approach 1:
The patent implements a multi-functional chopped-switched-capacitor circuit that simultaneously performs noise filtering, DC offset elimination, and temperature signal modulation. By combining multiple functions into a single circuit architecture, the patent achieves superior noise performance without proportionally increasing circuit complexity, as the same structural elements serve multiple purposes in the signal processing chain.
3Productivity
If high sample rates are used, then measurement speed improves, but noise performance deteriorates
Solution Approach 1:
The patent uses high-frequency periodic chopping that operates at a frequency much higher than both the temperature signal bandwidth and the desired sample rate. This allows the system to achieve high sample rates for rapid temperature monitoring while the periodic modulation continuously rejects low-frequency noise, maintaining noise performance even at high productivity levels.
Solution Approach 2:
The patent maintains continuous periodic chopping action throughout the measurement process, ensuring that noise rejection is constantly active regardless of the sample rate. This continuous useful action allows the system to operate at high sample rates for fast temperature tracking while consistently filtering out noise, thereby decoupling the relationship between sample rate and noise performance.
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 results in a temperature sensor with improved noise performance, higher sensitivity, and reduced power consumption, enabling accurate temperature measurement across a wide range with compact design.
Implementation Method 1
a switched capacitor network that provides or creates a low noise adaptable reference resistor for comparison purposes
Implementation Method 2
the temperature dependent characteristics (and/or changes therein) of the temperature sensitive device is resistance or change in resistance of the temperature sensitive device
Data Source
AI summary
The temperature-dependent resistance of a MEMS structure is compared with an effective resistance of a switched CMOS capacitive element to implement a high performance temperature sensor.