Capacitive Sensor Readout Using Summed Integration Cycles
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately measuring small and variable capacitance changes due to the limited resolution of A/D converters, leading to quantization errors and reduced distinguishability between capacitance values.
Innovation Solution
The method involves an integration process where a terminal of the capacitive sensor is connected to an integration capacitor with a known larger capacitance, and the voltage at the integration capacitor is measured after a preset number of cycles, allowing for a higher resolution measurement by accumulating and evaluating the total voltage over multiple integration cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single integration cycle is used to measure capacitance, then the measurement process is fast, but the measurement resolution is low due to quantization errors
Solution Approach 1:
The patent applies periodic action by performing multiple integration cycles repeatedly to accumulate charge transfers. Instead of a single measurement, the system executes the integration process multiple times and sums the voltage values, which averages out quantization errors and improves measurement resolution while maintaining reasonable measurement time through optimized cycle numbers.
Solution Approach 2:
The patent implements continuity of useful action by continuously accumulating voltage values from successive integration cycles. The measurement process maintains continuous charge transfer accumulation from the capacitive sensor to the integration capacitor across multiple cycles, ensuring that useful measurement information is gathered continuously rather than in isolated discrete events.
2Measurement precision
If multiple integration cycles are executed to improve measurement resolution, then quantization errors are compensated, but the measurement time increases
Solution Approach 1:
The patent applies partial action by executing a predetermined optimal number of integration cycles that provides sufficient measurement resolution without excessive measurement time. Rather than indefinitely increasing cycle numbers, the system determines an appropriate cycle count that achieves the required precision threshold, balancing resolution improvement with productivity maintenance.
3Adaptability or versatility
If the capacitance value of the sensor is very small and variable, then the sensor can detect subtle touches and proximity, but the measurement becomes more difficult due to limited A/D converter resolution
Solution Approach 1:
The patent applies merging by combining multiple voltage measurements from successive integration cycles into a single accumulated result. By summing the voltage values from multiple cycles, the system amplifies the small capacitance signals from the sensor, making them detectable above the quantization noise floor of the A/D converter and thereby improving both sensitivity and measurement reliability.
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 enhances the measurement resolution, effectively compensating for quantization errors and improving the ability to distinguish between capacitance values, thereby enhancing the sensitivity of capacitive touch sensor measurements.
Implementation Method 1
an integration capacitor (2) having a known capacitance value CI greater than the capacitance value CM of the sensor
Data Source
AI summary
A method for measuring a capacitance value of a capacitive sensor uses an integration process. For the integration process, the sensor is connected to an integration capacitor having a known capacitance value greater than the capacitance value of the sensor and a voltage UCI of the integration capacitor is measured by an A/D converter after a number IZ of executed integration cycles of the integration process. The method includes carrying out the integration process until the number IZ of executed integration cycles has reached the number N of integration cycles to be executed, adding a voltage value UCI (N) of the integration capacitor, which is determined by the A/D converter, to the total voltage value Utotal, increasing the number N, and repeating until the number N exceeds a predetermined value. The final total voltage value Utotal is indicative of the capacitance value of the capacitive sensor.