No-Ground Plane Differential Touchscreen Display for Noise Rejection
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Solution Overview
Problem
Existing sensor technologies face challenges in accurately detecting small changes and are prone to noise interference, particularly in touch screen applications, due to the use of single sensor circuits that are not sensitive enough and introduce common mode noise.
Innovation Solution
The implementation of differential drive-sense circuits (DDSCs) that utilize differential electrode pairs and phase-shifted reference signals to enhance sensitivity and reduce noise, allowing for precise detection of touch inputs by canceling out common mode noise and increasing signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single sensor circuits are used for touch detection, then device complexity is reduced, but measurement precision deteriorates due to insufficient sensitivity and common mode noise
Solution Approach 1:
The patent divides the sensing system into differential pairs of electrodes and corresponding differential sensor circuits. Each touch screen is segmented into multiple independent sensing channels, where each channel uses a differential electrode pair (first and second electrodes) with associated drive-sense circuits. This segmentation enables independent noise cancellation in each channel while maintaining overall system simplicity.
Solution Approach 2:
The patent changes the electrical parameters by using phase-shifted reference signals (e.g., 180 degrees out of phase) applied to differential electrode pairs. By modulating the drive signals with different phases and frequencies, the system can distinguish between common mode noise and actual touch signals, significantly improving measurement precision without requiring overly complex circuitry.
2Measurement precision
If differential drive-sense circuits with phase-shifted signals are implemented, then measurement precision improves through noise cancellation, but device complexity increases
Solution Approach 1:
The patent creates equipotential conditions by applying phase-shifted reference signals to differential electrode pairs. During non-touch periods, the drive-sense circuits maintain balanced potentials that cancel common mode noise. This equipotential approach allows simple circuit implementations to achieve high noise rejection ratios without requiring complex shielding or filtering networks.
Solution Approach 2:
The patent employs periodic switching of drive signals between different phases and frequencies. The drive-sense circuits alternately apply reference signals at different phases (e.g., in-phase and quadrature phases) to the electrode pairs. This periodic action enables time-multiplexed noise cancellation, where common mode noise is rejected during reference signal periods and touch detection occurs during sensing periods, simplifying the overall circuit architecture.
3Measurement precision
If traditional single-ended sensor circuits are used, then power consumption is lower, but measurement precision deteriorates due to noise susceptibility
Solution Approach 1:
The patent replaces traditional single-ended sensing mechanisms with differential sensing based on electromagnetic field interactions. By using capacitance changes between differential electrode pairs and applying phase-shifted AC signals, the system detects touch-induced impedance changes through field coupling rather than direct voltage measurements. This substitution enables high-precision detection with lower power consumption by exploiting natural electromagnetic phenomena rather than requiring high-power amplification circuits.
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 DDSCs provide enhanced sensitivity to small impedance changes, reducing noise and power consumption, thereby improving the accuracy and responsiveness of touch screen systems.
Implementation Method 1
differential electrode pairs...enhance sensitivity...detection of touch inputs by canceling out common mode noise
Data Source
AI summary
A no-ground plane differential touch screen display includes a display, a plurality of differential electrode pairs integrated into the display, a plurality of differential drive-sense circuits, and a processing module. When enabled, a set of differential drive-sense circuits of the plurality of differential drive-sense circuits is operable to provide a set of differential electrode signals to a set of differential electrode pairs of the plurality of differential electrode pairs and generate a set of sensed signals representative of electrical characteristic changes of the set of differential electrode pairs. The processing module is operable to interpret the electrical characteristic changes as one or more of a column mutual capacitance of a column differential electrode pair, a row mutual capacitance of a row differential electrode pair, and a cross mutual capacitance at a crossing between one or more row differential electrode pairs and column differential electrode pairs.