Capacitive Touch Voltage Measurement Using Comparator Timing
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Solution Overview
Problem
Current capacitive touch sensors face challenges in accurately measuring voltage changes due to external influences and require improved methods for determining touch or proximity positions without surface contact.
Innovation Solution
A system comprising a controller, analog multiplexer, comparator, sampling capacitors, and a measurement resistor/capacitor, which selectively charges and discharges capacitors to compare voltages across sense electrodes, enabling precise measurement of capacitance changes and position detection through adaptive charge cancellation and resistive/capacitive charging techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage measurement methods are used for capacitive touch sensors, then the measurement process is simple, but the measurement precision is insufficient due to external influences
Solution Approach 1:
The patent introduces a measurement capacitor as an intermediary element to transfer and compare voltage signals. The measurement capacitor is charged to the voltage on the sense electrode and then compared against a reference voltage, acting as a mediator that isolates the sensing electrode from direct measurement circuitry and enables precise voltage comparison without external interference
Solution Approach 2:
The patent performs preliminary charging of the measurement capacitor to match the sense electrode voltage before进行比较 with reference voltage. This preliminary action of charging the measurement capacitor to the target voltage level allows for accurate comparison to be made subsequently, ensuring measurement precision is achieved through preparatory voltage transfer
2Measurement precision
If measurement time is increased to improve accuracy, then measurement precision improves, but productivity decreases
Solution Approach 1:
The patent employs periodic charging and discharging cycles of the measurement capacitor to repeatedly measure voltage at different sense electrodes. This periodic action allows for rapid successive measurements across the touch sensor array, maintaining high productivity while achieving accurate capacitance change detection through repeated voltage comparison cycles
Solution Approach 2:
The patent replaces slow, traditional voltage measurement mechanisms with a faster capacitor-based voltage transfer and comparison system. By using capacitive charging through resistors and comparator-based voltage comparison, the system achieves rapid measurement without the time-consuming processes of traditional voltmeters or amplifiers, thereby maintaining high measurement throughput
3Measurement precision
If external influences are reduced to improve measurement accuracy, then measurement precision improves, but device complexity increases
Solution Approach 1:
The measurement capacitor serves as an intermediary that isolates the sense electrode from external measurement circuitry, preventing external electromagnetic influences from affecting the measurement. This capacitive coupling approach blocks external interference while allowing voltage transfer, achieving accurate measurements without requiring additional shielding or isolation components
Solution Approach 2:
The measurement system uses the inherent capacitive properties of the touch sensor electrodes and measurement capacitor itself to perform the measurement, rather than requiring external reference voltages or complex isolation circuits. The system leverages the natural voltage on the sense electrode and compares it through capacitor charging, making the measurement process self-contained and resistant to external influences
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 system enhances the speed and accuracy of voltage measurement across capacitive touch sensors, allowing for precise detection of touch or proximity without surface contact and reducing measurement time.
Implementation Method 1
a measurement capacitor CM. Each of sampling capacitors CS0-CSn has a terminal coupled to a corresponding one of sense lines Y0-Yn and another terminal coupled to a corresponding one of inputs M0-Mn to analog multiplexer 104
Implementation Method 2
The voltage across selected one of sampling capacitors CS0-CSn is increased by capacitive charging through an additional capacitor Cz coupled in series with the measurement capacitor CM
Implementation Method 3
The voltage across selected one of sampling capacitors CS0-CSn is increased by resistive charging through an additional resistor RF coupled in series with the measurement capacitor CM
Implementation Method 4
The output of analog multiplexer 104 is coupled to one of the inputs of comparator 102, and a terminal of measurement capacitor CM is coupled through terminal REF to another one of the inputs to comparator 106
Data Source
AI summary
In one embodiment, a method includes, at a first input of a comparator, receiving from an analog multiplexer one of multiple first voltages. Each of the first voltages results at least in part from an interaction between an object and an electrode of each of one or more nodes of a capacitive touch sensor. The method includes, at a second input of the comparator, receiving a second voltage across a measurement capacitor that has a first terminal coupled to the second input of the comparator. The method includes charging the measurement capacitor at least in part through a measurement resistor coupled in series to the first terminal of the measurement capacitor and monitoring an output of the comparator during the charging of the measurement capacitor. The output of the comparator changes state when the second voltage becomes approximately equal to or greater than the one of the first voltages. The method includes determining an amount of time from a start of the charging of the measurement capacitor to a change in state of the output of the comparator.