Capacitive Field Sensor With Sigma-Delta Linearized Readout
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional capacitance sensors face challenges in accurately calculating capacitance due to the exponential rise of voltage on the summing capacitor over time/cycles, requiring linearization, which complicates the measurement process.
Innovation Solution
A capacitive sensor with a sigma-delta modulator is introduced, which converts the capacitance measurement into a substantially linear duty cycle of a feedback pulse signal, using a switching capacitor circuit, sigma-delta modulator, and measurement circuit to determine capacitance changes effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If charge transfer technique is used to measure capacitance, then noise immunity is improved, but measurement linearity deteriorates due to exponential voltage rise on summing capacitor
Solution Approach 1:
The patent changes the measurement parameter from exponential voltage accumulation to linear voltage accumulation by modifying the charge transfer mechanism. Instead of directly accumulating charge on a summing capacitor, the invention uses a controlled charge transfer process where charge is transferred in discrete steps proportional to the input capacitance, creating a linear relationship between the number of transfer cycles and the measured capacitance value.
Solution Approach 2:
The patent introduces an intermediary charge transfer mechanism between the sensing capacitor and the measurement system. A transfer capacitor and controlled switching network serve as intermediaries that convert the exponential charge accumulation process into a linear counting process, where each transfer cycle moves a fixed amount of charge proportional to the input capacitance, enabling linear measurement while maintaining noise immunity.
2Measurement precision
If voltage accumulation on summing capacitor is used for capacitance measurement, then measurement capability is improved, but calculation complexity increases due to exponential relationship requiring linearization
Solution Approach 1:
The patent replaces the mathematical linearization process with a physical linear charge transfer mechanism. Instead of measuring exponential voltage accumulation and applying software or circuit-based linearization, the invention uses a controlled switching network that physically transfers charge in linear increments, making the measurement process inherently linear and eliminating the need for complex calculation or correction algorithms.
3Measurement precision
If conventional capacitance sensing is used, then basic measurement function is achieved, but accuracy deteriorates under environmental interference
Solution Approach 1:
The patent implements a feedback mechanism where the charge transfer process is controlled by comparing the accumulated charge against a reference threshold. The switching network monitors the voltage on the summing capacitor and automatically controls the charge transfer cycles, providing feedback that ensures accurate measurement even under environmental interference. This closed-loop approach maintains measurement accuracy by continuously adjusting the transfer process based on actual circuit conditions.
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 provides a linear relationship between the duty cycle and capacitance, simplifying the calculation and improving the accuracy of capacitance measurement, while also offering noise immunity and robustness against environmental interference.
Implementation Method 1
Capacitance sensors are used to implement a variety of useful functions including touch sensors, determining the presence of an object, accelerometers
Implementation Method 2
A capacitive sensor with a sigma-delta modulator is introduced, which converts the capacitance measurement into a substantially linear duty cycle of a feedback pulse signal
Data Source
AI summary
A capacitive sensor includes a switching capacitor circuit, a comparator, and a charge dissipation circuit. The switching capacitor circuit reciprocally couples a sensing capacitor in series with a modulation capacitor during a first switching phase and discharges the sensing capacitor during a second switching phase. The comparator is coupled to compare a voltage potential on the modulation capacitor to a reference and to generate a modulation signal in response. The charge dissipation circuit is coupled to the modulation capacitor to selectively discharge the modulation capacitor in response to the modulation signal.