Resistive Sensor Interface With Stable Frequency Readout
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Solution Overview
Problem
High-cost and high-power consumption of existing resistive sensors limit their deployment in dense networks for applications like air quality monitoring, as they are not economically viable for widespread use due to their size and power requirements.
Innovation Solution
A low-power, low-cost universal resistive sensor interface with an analog front end and a Smart Digital Controller (SDC) that oscillates at a frequency proportional to sensor resistance, featuring variable integrator capacitance and gain to stabilize and compute sensor resistance, allowing for efficient interfacing with resistive sensors and reducing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-cost and high-power consumption resistive sensors are used, then measurement precision is improved, but device cost and power consumption increase
Solution Approach 1:
The patent replaces traditional high-power analog signal conditioning circuits with a digital oscillator-based measurement system. The sensor resistance is converted to an oscillation frequency through an RC integrator circuit, allowing digital measurement instead of analog processing. This substitution reduces power consumption while maintaining measurement precision through frequency-based digital readout.
Solution Approach 2:
The patent transforms the sensor resistance parameter into an oscillation frequency parameter through the RC integrator circuit. By measuring frequency instead of resistance directly, the system achieves high precision measurement with lower power consumption, as frequency measurement can be performed digitally with minimal power requirements.
2Measurement precision
If high-cost and high-power consumption resistive sensors are used, then measurement precision is improved, but device cost increases
Solution Approach 1:
The patent replaces expensive precision analog measurement circuits with a digital oscillator and counter system. The use of standard digital components (oscillator, counter, comparator) instead of precision analog instruments reduces manufacturing cost while achieving comparable or superior measurement precision through frequency-based measurement.
Solution Approach 2:
The patent employs inexpensive RC components (resistors and capacitors) to create the oscillation circuit, replacing expensive precision measurement instruments. The system uses readily available, low-cost components that can be easily manufactured and replaced, significantly reducing device cost.
3Productivity
If sampling frequency is increased, then productivity is improved, but measurement error increases
Solution Approach 1:
The patent uses digital frequency measurement with counters to achieve high-speed sampling without the measurement errors associated with analog systems. The digital counter can accurately measure oscillation cycles even at high sampling rates, eliminating analog noise and drift issues that typically increase measurement error at higher frequencies.
Solution Approach 2:
The patent employs periodic oscillation from the RC integrator circuit, where each oscillation cycle represents a measurement period. By counting complete cycles over a fixed time interval, the system achieves high sampling frequency with accurate measurement, as the periodic nature provides inherent synchronization and eliminates timing errors.
4Adaptability or versatility
If dynamic range is increased, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent achieves wide dynamic range by measuring oscillation frequency, which can be accurately measured across a broad range of RC time constants. By varying the integration time or oscillation period rather than using multiple gain stages or complex amplification circuits, the system extends dynamic range while maintaining relatively simple circuit architecture.
Solution Approach 2:
The periodic oscillation allows the system to measure both very small and very large resistance values by adjusting the measurement window or integration time. The counter can accurately count cycles whether the oscillation is fast (low resistance) or slow (high resistance), providing wide dynamic range through temporal integration rather than spatial complexity.
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 enables a fivefold improvement in sampling frequency and a threefold decrease in measurement error, with a 20 dB increase in dynamic range, making it suitable for dense networks of low-cost sensors, such as those used in air quality monitoring, while maintaining power consumption below 5.5 mW.
Implementation Method 1
An integration stage is coupled to the analog I/O sensor port to oscillate at an oscillation frequency proportional to a sensor resistance of the resistive sensor
Data Source
AI summary
A sensor interface for a resistive sensor has an analog front end comprising. The analog front end has an analog input/output (I/O) sensor port to be coupled to the resistive sensor. An integration stage is coupled to the analog I/O sensor port to oscillate at an oscillation frequency proportional to a sensor resistance of the resistive sensor. The integration stage has a variable integrator capacitance to vary the oscillation frequency. A gain stage is coupled to the integration stage and has a variable gain to vary the oscillation frequency of the integration stage. The sensor interface also has a smart digital controller (SDC) coupled to the analog front end to compute the sensor resistance of the resistive sensor based on the oscillation frequency. In addition, the SDC automatically detects unstable oscillation in the integration stage and causes the variable gain and the variable integrator capacitance to change.