Differential Capacitance Measurement With Reset Phases for Precision
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current capacitive sensor measurement systems, particularly those using the Charge-Based Capacitance Measurement (CBCM) technique, face challenges such as sensitivity degradation due to temperature and process variations, and require high voltages that can push the differential amplifier into a nonlinear region, limiting resolution and accuracy.
Innovation Solution
A measurement system with a switching circuit and differential integrator that uses control signals to manage capacitance charging and discharging cycles, incorporating a comparator with hysteresis and decoupling capacitances to mitigate noise and offset issues, and an asynchronous reset mechanism to improve sensitivity and detection speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high voltages are used to charge the capacitance, then the charging speed and detection sensitivity are improved, but the differential amplifier is pushed into a nonlinear region which limits resolution and accuracy
Solution Approach 1:
The patent implements periodic charging and discharging cycles of the capacitance through controlled switching phases. The capacitance is charged during specific phases and discharged during other phases, creating a periodic action that enables measurement while preventing continuous high voltage exposure that would cause nonlinear distortion in the differential amplifier.
Solution Approach 2:
The patent dynamically controls the voltage applied to the capacitance by using switching circuits to alternate between charging and discharging states. This dynamic approach allows the system to apply high voltage only when necessary for charging, then switch to low voltage or ground for discharge and measurement, thereby maintaining amplifier linearity while achieving fast charging.
2Reliability
If temperature and process variations are present, then the measurement stability deteriorates, but adding compensation circuits increases system complexity
Solution Approach 1:
The patent employs self-service mechanisms where the measurement system automatically compensates for temperature and process variations through its inherent switching and integration architecture. The differential integrator and switching circuitry work together to naturally reject common-mode variations, providing temperature compensation without requiring external compensation circuits or additional components.
Solution Approach 2:
The patent implements feedback mechanisms through the differential integrator that continuously monitors and adjusts for variations. The integration process inherently averages out temperature and process variations over the measurement cycle, providing automatic compensation that maintains measurement stability without adding complex external feedback circuits.
3Productivity
If switching operations are performed to charge and discharge the capacitance, then the measurement speed is improved, but noise and charge injection mismatch increase
Solution Approach 1:
The patent extracts and separates the harmful effects of switching operations by using dedicated discharge phases and reset mechanisms. The switching circuitry is designed to complete discharge operations before measurement phases, extracting charge injection artifacts and noise from the measurement signal path. This separation allows fast switching for charging while preventing noise contamination during the actual measurement.
Solution Approach 2:
The patent implements rapid discharge and reset phases that quickly skip through the potentially noisy transition periods. By rushing through the discharge phase and completing switching operations in minimal time, the system reduces the duration during which noise and charge injection mismatch can affect the measurement, thereby maintaining high measurement speed while minimizing harmful effects.
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 system achieves improved sensitivity and faster detection of capacitance differences, reducing the impact of temperature and process variations, and maintaining accuracy while minimizing thermal noise and charge injection mismatch.
Implementation Method 1
a first terminal of the first capacitance to a first voltage and a first terminal of the second capacitance to a second voltage
Data Source
AI summary
A measurement system, featuring first and second capacitances, and switching, control, and measurement circuits, charges/discharges the capacitances during normal operation. The switching and control circuits periodically connect a first terminal of the first capacitance to a first voltage and a reference voltage, and a first terminal of the second capacitance to a second voltage and the reference voltage. The second terminal of the first capacitance and the second terminal of the second capacitance are connected to the input terminals of the differential integrator, the charge difference between the capacitances being transferred to the differential integrator. A comparator triggers when the output signal of the differential integrator exceeds the hysteresis threshold of the comparator. Two decoupling capacitances are connected between the input of the comparator and the output of the differential integrator, and two reset phases are used to store various disturbances to these decoupling capacitances, improving precision.