Capacitive Sensor Circuit With Boxcar Integration for Low-Noise Linearity
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Solution Overview
Problem
Existing capacitive sensor circuits face challenges in achieving high linearity, low noise sensitivity, and compact design while managing power consumption and complexity, particularly in open-loop and closed-loop architectures.
Innovation Solution
A circuit configuration that alternates between two modes, utilizing a GM stage to convert sensor voltage to current, charging a boxing capacitor, and an integrator to integrate voltage over time, with a hold circuit to provide feedback voltage and reset the capacitor, thereby reducing noise and enhancing linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a force feedback architecture is used to improve linearity and sensitivity, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The circuit operates in two distinct time intervals: a first time interval for charging the boxing capacitor with the sensor current, and a second time interval for discharging the boxing capacitor and integrating the voltage. This temporal segmentation allows the circuit to achieve force feedback-like measurement precision without the continuous complexity of traditional force feedback architectures.
Solution Approach 2:
The circuit employs periodic switching between two operational modes: charging mode during the first time interval and discharging/integrating mode during the second time interval. This periodic action enables the boxing capacitor to accumulate charge proportional to the sensor output while maintaining circuit simplicity through alternating operations rather than continuous feedback.
2Device complexity
If an open-loop architecture is used to reduce complexity and power consumption, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The circuit implements a feedback mechanism through the hold circuit that provides feedback voltage to the capacitive sensor based on the integrated output from the second time interval. This feedback improves linearity and measurement precision while maintaining the simpler open-loop structural framework, combining benefits of both architectures.
Solution Approach 2:
The boxing capacitor serves as an intermediary element that converts the sensor voltage output into accumulated charge during the first time interval, which is then converted to voltage by the integrator during the second time interval. This intermediary mechanism enables precise measurement without requiring complex continuous feedback circuitry.
3Measurement precision
If boxcar sampling is implemented to reduce noise, then output noise is reduced, but device complexity increases
Solution Approach 1:
The circuit merges the boxcar sampling function with the integration function by using the same boxing capacitor and integrator circuitry. During the first time interval, the capacitor accumulates charge through boxcar sampling; during the second time interval, the integrator processes this charge. This merging achieves noise reduction without adding separate dedicated circuits.
Solution Approach 2:
The boxcar sampling operation is implemented through periodic charging of the boxing capacitor during the first time interval, followed by periodic discharging and integration during the second time interval. This periodic boxcar sampling reduces noise by averaging effects over the charging period while maintaining circuit simplicity through time-division operation.
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 achieves high linearity, stability against vibrations and electromagnetic interference, low output noise, and a compact sensor device with reduced surface area, meeting automotive requirements.
Implementation Method 1
The GM stage is configured to receive a sensor voltage of the capacitive sensor at the first input contact of the GM stage and to convert the sensor voltage into a sensor current
Implementation Method 2
charge a first boxing capacitor with the sensor current in the second time interval
Implementation Method 3
the integrator is configured, in the second time interval, to integrate a voltage applied across the first boxing capacitor over its time curve and to output an output voltage resulting therefrom
Implementation Method 4
The hold voltage is configured to tap the output voltage of the integrator in the second time interval and to hold it as a hold voltage at an output of the hold circuit
Implementation Method 5
A circuit according to an example embodiment of the present invention for operating a capacitive sensor
Data Source
AI summary
A circuit for operating a capacitive sensor configured to be operated alternately in a first mode over a first time interval and in a second mode over a second time interval. The circuit includes a GM stage configured to receive a sensor voltage of the capacitive sensor at a first input contact and convert the sensor voltage into a sensor current to charge a first boxing capacitor with the sensor current in the second time interval, an integrator that is configured to, in the second interval, integrate a voltage applied across the first boxing capacitor over its time curve and output a resulting output voltage at a first output, and a hold circuit configured to tap the output voltage of the integrator in the second interval and hold it as a hold voltage.