Capacitive Touch Pad Sensing Without Negative Voltage Measurement
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Solution Overview
Problem
Capacitive touch pads face challenges in detecting objects due to the need to measure negative voltages, which complicates the measuring circuit and limits detection sensitivity, and integrating a proximity detection function increases system complexity, size, cost, and current consumption.
Innovation Solution
A method that charges the sampling capacitor between two voltages, allowing charge transfer between electrodes and the capacitor, and measures capacitance based on the voltage at the capacitor's terminals after a fixed number of cycles or until a threshold is reached, simplifying the circuit and enabling proximity detection without increasing system complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the touch pad measures negative voltages to detect capacitance changes, then detection capability is maintained, but the measuring circuit becomes more complex and detection sensitivity is limited
Solution Approach 1:
The patent inverts the traditional measurement approach by measuring positive voltage drops instead of negative voltage rises. The sampling capacitor is charged to a reference voltage and then allowed to discharge through the electrode capacitance during transfer cycles. The voltage drop from the reference level is measured as a positive value, eliminating the need for complex negative voltage measurement circuitry while maintaining detection accuracy.
Solution Approach 2:
The patent applies preliminary action by pre-charging the sampling capacitor to a known reference voltage before the charge transfer process. This initial charging establishes a baseline from which subsequent voltage drops can be easily measured. The reference voltage is maintained throughout the measurement process, allowing for straightforward comparison and simplifying the measuring circuit design.
2Adaptability or versatility
If a dedicated proximity detection electrode is integrated into the system, then proximity detection function is added, but system complexity, size, cost, and current consumption increase
Solution Approach 1:
The patent makes the existing electrode structure multi-functional by enabling it to serve both as a touch detection electrode and a proximity detection electrode. The same electrode pairs used for contactless touch detection can detect proximity by measuring capacitance changes at greater distances. This eliminates the need for dedicated proximity detection electrodes and their associated circuitry, reducing system complexity, size, and cost.
Solution Approach 2:
The patent merges the touch detection function and proximity detection function into a single integrated system. By using the same electrode structure and control circuitry for both functions, the system achieves versatility without increasing complexity. The control circuit can switch between touch detection mode and proximity detection mode using the same hardware resources.
3Measurement precision
If multiple charge and transfer cycles are executed to improve measurement accuracy, then measurement precision improves, but measurement time increases
Solution Approach 1:
The patent maintains continuity of useful action by executing charge and transfer cycles in rapid succession without idle periods between cycles. The sampling capacitor is continuously charged and transferred through the electrode capacitance multiple times, with each cycle building upon the previous one. This continuous operation accumulates measurement information efficiently, improving accuracy without significant time penalty.
Solution Approach 2:
The patent employs periodic action by repeating the charge and transfer cycles at regular intervals. A fixed number of cycles are executed in sequence, with each cycle following the same timing pattern. This periodic repetition allows for consistent and reliable measurements while maintaining a predictable measurement time that can be optimized by adjusting the number of cycles.
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 simplifies the measuring circuit, enhances detection sensitivity, and integrates proximity detection without increasing system size, cost, or current consumption, allowing for effective object detection and position determination on capacitive touch pads.
Implementation Method 1
a sampling capacitor (Cs) the other terminal of which is connected to the ground. The ports P1 to Pn are connected to the row electrodes R1-Rn
Implementation Method 2
the presence of an object on the touch pad can change the capacitance of pairs of electrodes located near the object
Data Source
AI summary
The present disclosure relates to a method for measuring a capacitance of a pair of electrodes including charging the pair of electrodes and transferring the charge between the pair of electrodes and a sampling capacitor, and a measuring step representative of the capacitance of the pair of electrodes according to the voltage at the terminals of the sampling capacitor according to the number of cycles executed so that the voltage at the terminals of the sampling capacitor reaches a threshold voltage. According to the present disclosure, the method comprises an initial step of charging the sampling capacitor between a first voltage and a second intermediate voltage in between the first voltage and a third voltage greater than or equal to a ground voltage, the pair of electrodes being charged between the second voltage and the third voltage. The present disclosure applies in particular to the control of a touch pad.