Capacitive Touch Sensing With Differential Signal Subtraction
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately distinguishing genuine capacitance changes from noise interference, leading to unreliable touch detection, and existing solutions to enhance signal amplitude increase costs and circuit board footprint.
Innovation Solution
A touch-sensitive apparatus using a differential amplifier to subtract a reference signal from a sensor signal, improving noise immunity and resolution by enhancing the signal-to-noise ratio without increasing signal amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amplitude of the signal applied to the electrode array is increased to improve noise immunity, then the signal-to-noise ratio is improved, but the cost and circuit board footprint increase
Solution Approach 1:
The patent changes the temporal characteristics of the signal rather than increasing amplitude. By applying a time-varying drive signal and analyzing the time-varying response, the system achieves improved noise immunity through signal processing in the time domain rather than amplitude enhancement, thus avoiding increased circuit board footprint
Solution Approach 2:
The patent replaces the physical approach of increasing signal amplitude with a signal processing approach using time-varying signals and temporal analysis. This substitution allows noise filtering through temporal characteristics rather than relying on higher amplitude signals, reducing the need for larger circuits
2Measurement precision
If signal processing techniques are applied to distinguish genuine capacitance changes from noise, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic time-varying drive signals applied to the electrode array. By using periodic excitation and analyzing the periodic response characteristics, the system can distinguish genuine capacitance changes from noise through temporal pattern recognition, achieving improved measurement precision with relatively simple periodic signal generation and analysis
Solution Approach 2:
The patent implements a feedback mechanism where the time-varying drive signal is applied and the resulting time-varying response is analyzed. The control circuitry uses this feedback information to determine genuine capacitance changes versus noise, improving touch detection accuracy through iterative temporal analysis without requiring complex processing
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
The differential amplifier effectively filters out noise, enhancing the accuracy and reliability of touch detection while maintaining a compact circuit design.
Implementation Method 1
a differential amplifier comprising: a first input configured to receive a time-varying sensor signal from an electrode of the electrode array, the sensor signal indicative of a capacitive coupling associated with the at least one electrode; a second input configured to receive a time-varying reference signal; a first output configured to output a first output signal from the differential amplifier based on a difference between the time-varying sensor signal and the time-varying reference signal
Implementation Method 2
capacitive touch sensors for overlying a display screen to provide a touch-sensitive display (touch screen)... measure changes in the electrical capacitance of each of the electrodes or the mutual-capacitance between combinations of the electrodes
Data Source
AI summary
Described is a touch-sensitive apparatus for sensing the presence of an object relative to a touch-sensitive surface using capacitance measurements. The apparatus includes an electrode array comprising at least one electrode, the electrode array providing the touch-sensitive surface; a signal generating module for generating a time-varying drive signal to be applied to the electrode array; a differential amplifier comprising: a first input configured to receive a time-varying sensor signal from an electrode of the electrode array, the sensor signal indicative of a capacitive coupling associated with the at least one electrode; a second input configured to receive a time-varying reference signal; a first output configured to output a first output signal from the differential amplifier based on a difference between the time-varying sensor signal and the time-varying reference signal; and control circuitry configured to determine the presence of an object, wherein the apparatus further comprises a subtractor for subtracting a signal from the first output signal from the differential amplifier to generate a subtracted signal, wherein the control circuitry is configured to receive a signal based on the subtracted signal and to determine the presence of an object based on the received signal. Further disclosed is a method for sensing the presence of an object relative to a touch-sensitive surface using capacitance measurements of a touch sensitive apparatus.