Capacitor Sensing With Charge Equalization
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Solution Overview
Problem
Capacitive sensing systems face challenges in reducing the number of external terminals required for integrated circuits and efficiently determining sensor activation, especially when dealing with multiple capacitive sensors in concurrent phases.
Innovation Solution
The system employs a method where a second capacitive sensor is used for charge equalization, allowing a single external terminal per capacitive sensor, and utilizes a multiplexed ADC to perform multiple phases concurrently, enabling efficient digitization of voltage values indicative of capacitance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitive sensing systems use separate external terminals for each sensor, then each sensor can be independently measured, but the number of external terminals increases and system complexity increases
Solution Approach 1:
The patent merges the functions of multiple external terminals into a single shared terminal. By using a time-division multiplexing approach where capacitive sensors are charged and measured in sequential phases, the system eliminates the need for separate external terminals for each sensor, reducing terminal count while maintaining measurement capability
Solution Approach 2:
The single external terminal serves multiple functions: it charges different capacitive sensors at different times, measures voltage for multiple sensors sequentially, and facilitates charge equalization between sensors. This multi-functional use of a single terminal resolves the contradiction between terminal reduction and measurement capability
2Productivity
If multiple capacitive sensors are measured simultaneously with separate ADCs, then measurement speed increases, but device complexity and cost increase
Solution Approach 1:
The system uses periodic time-division multiplexing where capacitive sensors are charged and measured in alternating phases. Each sensor undergoes charge equalization with its partner, then voltage measurement occurs in a periodic sequence, enabling multiple sensors to be measured efficiently with a single ADC without simultaneous measurement requirements
Solution Approach 2:
The measurement process is segmented into distinct phases: charge equalization phase where sensors exchange charge with their partners, and measurement phase where voltage is read by the ADC. This temporal segmentation allows a single ADC to handle multiple sensors sequentially while maintaining measurement integrity
3Measurement precision
If charge equalization is performed between capacitive sensors, then measurement accuracy improves, but additional time and phases are required
Solution Approach 1:
The charge equalization process is integrated into the normal measurement cycle rather than being a separate preparatory step. Sensors continuously undergo charge equalization with their partners during designated phases, ensuring measurement accuracy is maintained without requiring additional time beyond the regular measurement periodicity
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 reduces the number of external terminals needed, allows for concurrent phase execution, and effectively determines sensor activation, enhancing the efficiency and sensitivity of capacitive sensing systems.
Implementation Method 1
A capacitive sensor is a device that becomes capacitively coupled with a conductive or dielectric external object and whose capacitance changes with the movement of the external object with respect to the capacitive sensor
Data Source
AI summary
As disclosed herein, circuitry and a method for providing a digitized voltage value of one capacitive sensor in which a second capacitive sensor is utilized for charge equalization. After charge equalization, an analog to digital converter (ADC) provides a digital value representative of the voltage of the one sensor.