Capacitive Touch Voltage Measurement With Precharged Comparator Input
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Solution Overview
Problem
Current voltage measurement techniques in capacitive touch sensors are limited by the time required to change the state of the comparator, which restricts the rate at which voltages across sampling capacitors can be measured, especially in touch-sensitive applications where rapid detection of touch or proximity is essential.
Innovation Solution
The system employs a combination of capacitive and resistive charging methods, using additional capacitors and resistors to accelerate the charging of the measurement capacitor, thereby reducing the time needed to reach the comparison voltage and improving measurement efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage measurement techniques are used in capacitive touch sensors, then measurement accuracy is maintained, but the measurement time is excessive which restricts the measurement rate
Solution Approach 1:
The patent applies preliminary action by pre-charging the measurement capacitor to a known voltage level before the actual measurement process. This preparation step allows the comparator to start from a predetermined state, significantly reducing the time required to reach the comparison threshold while maintaining measurement accuracy. The measurement capacitor is charged to a voltage close to the expected measurement value, so the comparator needs to detect only the small difference, thereby speeding up the measurement process.
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the measurement capacitor's initial voltage based on the expected touch signal range. By changing the reference voltage parameter and the measurement capacitor's charge level according to different measurement scenarios, the system optimizes the comparison process to occur within a narrower voltage range, thus reducing measurement time while preserving precision.
2Productivity
If the comparator state change time is reduced to improve measurement rate, then measurement speed increases, but measurement precision may be compromised
Solution Approach 1:
The system performs preliminary charging of the measurement capacitor to a voltage close to the expected touch signal level before measurement. This allows the comparator to detect small voltage changes rapidly without sacrificing precision, because the comparison starts from a optimized initial state rather than from zero or a far-off voltage level.
Solution Approach 2:
The measurement capacitor serves as an intermediary element that bridges the touch sensor output and the comparator input. By pre-charging this intermediary capacitor to an optimal voltage, the system enables the comparator to operate in its most sensitive range, thus achieving both high measurement rate and high precision simultaneously.
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 significantly reduces the elapsed time for voltage measurement across sampling capacitors, enhancing the system's ability to detect touch or proximity events in real-time, particularly in touch-sensitive applications like touch screens.
Implementation Method 1
a measurement capacitor CM coupled between terminal REF and terminal MEAS
Implementation Method 2
The system employs a combination of capacitive and resistive charging methods, using additional capacitors and resistors to accelerate the charging of the measurement capacitor
Implementation Method 3
The system employs a combination of capacitive and resistive charging methods, using additional capacitors and resistors to accelerate the charging of the measurement capacitor
Data Source
AI summary
In one embodiment, a method includes receiving one of a number of first voltages. Each of the first voltages results at least in part from a signal applied to an electrode of each of one or more nodes of a capacitive touch sensor. The method also includes receiving a second voltage across a measurement capacitor. The second voltage results at least in part on charging the measurement capacitor through application of a pre-determined voltage. The method also includes monitoring an output voltage during the charging of the measurement capacitor. The output voltage changes state based at least in part on a comparison of the second voltage relative to the one of the first voltages.