Input Device EMI Reduction via Constant Voltage Data Lines
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Solution Overview
Problem
Existing input devices face challenges in reducing electromagnetic interference (EMI) during the transition from display updating to input sensing, which affects the accuracy and reliability of capacitive sensing operations.
Innovation Solution
The solution involves controlling the slew rate of voltage transitions on sensor electrodes by driving data lines with a constant voltage, specifically transitioning from a common voltage to a first constant voltage before applying a sensing signal, and then back to the common voltage, while outputting a guard signal with varying voltage characteristics during non-display update periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the display updates and sensor electrode transitions voltage simultaneously, then device complexity is reduced, but electromagnetic interference increases affecting sensing accuracy
Solution Approach 1:
The non-display update period is divided into multiple portions: a first portion for sensing operations with varying voltage on the sensor electrode, and second and third portions for transitioning to and from constant voltage states. This temporal segmentation allows sensing to occur during periods when display data lines are stable, reducing EMI without requiring separate dedicated slew rate control circuitry.
Solution Approach 2:
The source driver outputs a guard signal during the first portion of the non-display update period before the sensor electrode voltage transition occurs. This preliminary action prepares the sensing circuitry and establishes a reference signal that accounts for capacitive coupling effects, enabling accurate sensing while the display data lines are held at constant voltage and minimizing EMI interference.
2Object-affected harmful factors
If slew rate control circuitry is added to reduce EMI, then electromagnetic interference decreases, but device complexity and manufacturing cost increase
Solution Approach 1:
The source driver is designed to perform multiple functions: driving display data lines during display update periods, holding data lines at constant voltage during non-display update periods, and outputting guard signals during sensing operations. This multi-functionality eliminates the need for separate dedicated slew rate control circuitry, reducing device complexity and manufacturing cost while still achieving EMI reduction through coordinated voltage control.
3Measurement precision
If the sensor electrode uses varying voltage for sensing, then sensing capability is improved, but electromagnetic interference increases
Solution Approach 1:
The guard signal acts as an intermediary during the first portion of the non-display update period. It is output by the source driver during the same time the sensor electrode receives the varying sensing signal. The guard signal compensates for capacitive coupling effects between the data lines and sensor electrode, allowing accurate sensing to proceed while the data lines are held at constant voltage, thereby maintaining sensing accuracy without generating additional EMI.
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 reduces EMI generated by the input device, enhances sensing accuracy, and allows for the integration of capacitive sensing and display updating without the need for dedicated slew rate control circuitry, thereby reducing manufacturing costs and increasing the device's applicability in various electronic systems.
Implementation Method 1
capacitive sensing devices
Implementation Method 2
reduces EMI generated by the input device
Data Source
AI summary
An input device comprises a plurality of data lines of a display panel, a plurality of sensor electrodes, and a processing system. The processing system drives a sensor electrode with a sensing signal during a first portion of a non-display update period of a display frame. In certain embodiments, a source driver of the processing system drives a data line with a first constant voltage during at least one of a second portion of the non-display update period and a third portion of the non-display update period. In certain embodiments, the source driver outputs a guard signal during the first portion of the non-display update period. The first portion of the non-display update period occurs after the second portion of the non-display update period and before the third portion of the non-display update period.