Differential Self-Capacitance Scanning for Touch Panel EMI Reduction
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Solution Overview
Problem
Large touch panels face challenges with excessive radiated electromagnetic emission and susceptibility to external noise, limiting their performance and increasing power consumption, especially in capacitive sensing devices using square-wave excitations.
Innovation Solution
Implementing differential self-capacitance scanning using differential waveforms to drive adjacent electrodes, which reduces electromagnetic interference (EMI) and enhances signal-to-noise ratio (SNR) by canceling parasitic charges and eliminating the need for additional baselining circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If square-wave excitations are used in capacitive sensing devices, then the sensing operation is simplified, but radiated electromagnetic emission increases and susceptibility to external noise increases
Solution Approach 1:
The patent changes the waveform parameter from square-wave to differential waveform (e.g., sine wave or triangular wave) to reduce electromagnetic radiation and improve noise immunity while maintaining sensing functionality
Solution Approach 2:
The patent uses differential signaling to convert the harmful effect of electromagnetic radiation into a beneficial effect by canceling out radiated emissions through opposite-phase signal application on adjacent electrodes
2Ease of operation
If square-wave excitations are used in capacitive sensing devices, then the sensing operation is simplified, but power consumption increases
Solution Approach 1:
The patent changes the excitation waveform from square-wave to differential waveform, which reduces power consumption while maintaining sensing operation simplicity
Solution Approach 2:
The differential waveform approach converts the high power consumption of square-wave excitations into lower power consumption by utilizing the differential nature of the signals to reduce overall energy requirements
3Area of stationary object
If large touch panels are used, then the display area is increased, but radiated electromagnetic emission increases
Solution Approach 1:
The patent applies differential signaling to large touch panels to convert the harmful radiated electromagnetic emission into a beneficial effect by canceling out emissions through opposite-phase signal application on adjacent electrodes, enabling large panel sizes without excessive EMI
4Object-generated harmful factors
If additional baselining circuitry is added to reduce EMI, then electromagnetic interference is reduced, but device complexity increases
Solution Approach 1:
The patent enables the touch panel to reduce its own EMI through differential signaling without requiring external baselining circuitry, as the differential nature of the signals inherently cancels out parasitic charges and electromagnetic emissions
Solution Approach 2:
The patent converts the harmful EMI into a beneficial effect through differential signaling, eliminating the need for additional baselining circuitry by using the differential signals themselves to cancel out parasitic charges
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 significantly reduces panel radiation, improves noise performance, and supports multi-touch capabilities without the need for additional tuning, making it suitable for various panel sizes and configurations.
Implementation Method 1
When a conductive object, such as a finger, comes in contact or close proximity with the touch-sensing surface, the capacitance of one or more capacitive touch sensor elements changes
Implementation Method 2
generates a first waveform and a second waveform that are opposite phases of each other, applies the first waveform to a first transmitter electrode and the second waveform to a second transmitter electrode adjacent to the first transmitter electrode
Data Source
AI summary
Apparatuses and methods of differential driving of adjacent electrodes for low electromagnetic interference (EMI) for scanning a touch panel are described. One apparatus generates an in-phase drive signal and an opposite-phase drive signal and applies, at a substantially same time, the in-phase drive signal to a first transmitter electrode and the opposite-phase drive signal to a second transmitter electrode adjacent to the first transmitter electrode. The apparatus receives a first sense signal from a first receiver electrode and a second sense signal from a second receiver electrode adjacent to the first receiver electrode. The apparatus combines the first sense signal and the second sense signal to obtain a third sense signal. The third sense signal represents a first self capacitance associated with the first receiver electrode. The apparatus detects a presence of an object on a touch panel using at least the first self capacitance.