Multi-phase Touch Scanning with Zero-sum Sequences
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Solution Overview
Problem
Large capacitance-sensing touch panels face challenges with excessive radiated electromagnetic emission and susceptibility to external common-mode noise, limiting their performance and compliance with electromagnetic emission standards, especially in larger screen sizes.
Innovation Solution
Implementing multi-phase scanning with zero-sum sequences that minimize electromagnetic emission by using a combination of in-phase, opposite-phase, and reference signals, allowing for simultaneous excitation of multiple electrodes with different phases, and applying appropriate filtering techniques to suppress noise and reconstruct touch signals effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional single-phase or two-phase scanning is used in large capacitance-sensing touch panels, then the circuit design is simpler, but radiated electromagnetic emission becomes excessive and the device is susceptible to external common-mode noise
Solution Approach 1:
The patent divides the electrode excitation into multiple phases (at least three phases) with different excitation sequences. Each phase excites a different subset of electrodes with specific timing, segmenting the overall excitation process to reduce peak electromagnetic emissions through time-diversified excitation patterns.
Solution Approach 2:
The patent employs periodic multi-phase excitation sequences where electrodes are excited in repeating cycles with specific phase relationships. This periodic multi-phase action creates a more distributed electromagnetic emission profile over time, reducing peak emissions compared to continuous single-phase excitation.
2Device complexity
If traditional scanning methods are used, then the implementation is simpler, but susceptibility to external common-mode noise increases
Solution Approach 1:
The patent segments the excitation and sensing operations into multiple phases with different timing sequences. By distributing the excitation across multiple phases rather than using a single continuous excitation, the system creates temporal diversity that helps differentiate touch signals from common-mode noise, improving noise rejection.
Solution Approach 2:
The patent implements a feedback mechanism where the system measures capacitance changes during multi-phase scanning and uses this information to reconstruct touch signals while filtering out common-mode noise. The multi-phase measurements provide redundant information that can be processed to eliminate noise components.
3Object-generated harmful factors
If multi-phase scanning with zero-sum sequences is implemented, then electromagnetic emission is reduced and electromagnetic immunity is enhanced, but the scanning and excitation process becomes more complex
Solution Approach 1:
The patent changes the excitation parameters by introducing multiple phases with specific phase relationships and zero-sum sequences. This parameter change transforms the excitation pattern from simple continuous signaling to structured multi-phase sequences, reducing electromagnetic emission through controlled parameter variation.
4Measurement precision
If multi-phase scanning is used, then signal-to-noise ratio is improved, but the processing and reconstruction of touch signals becomes more complex
Solution Approach 1:
The patent uses feedback-based signal reconstruction where multi-phase capacitance measurements are processed to reconstruct touch signals. The system measures capacitance during each phase, compares measurements, and reconstructs the touch signal while filtering out noise, using the redundant phase information to improve measurement precision.
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 electromagnetic emission while enhancing electromagnetic immunity, supporting both mutual and self-capacitance sensing, and enabling reliable operation on large touch screens with improved signal-to-noise ratio and noise reduction.
Implementation Method 1
capacitance-sensing devices are intended to replace mechanical buttons, knobs, and other similar mechanical user-interface controls. Capacitance-sensing devices eliminate the complicated mechanical switches and buttons, providing reliable operation under harsh conditions.
Implementation Method 2
The mutual capacitance change is detected in the mutual capacitance-sensing mode. Each sensor element uses at least two electrodes: one is a transmitter (TX) electrode (also referred to herein as transmitter electrode) and the other is a receiver (RX) electrode. When a finger touches a sensor element or is in close proximity to the sensor element, the capacitive coupling between the receiver and the transmitter of the sensor element is decreased as the finger shunts part of the electric field to ground
Data Source
AI summary
Apparatuses and methods of multi-phase scanning of a touch panel are described. One apparatus selects a sequence having a number of one values, negative one values, and zero values. The one values correspond to an in-phase drive signal, the negative one values correspond to an opposite-phase drive signal, and the zero values correspond to a reference signal (e.g., reference voltage or ground). A sum of the sequence is equal to zero. The apparatus applies one of the in-phase drive signal, the opposite-phase drive signal, or the reference signal to each of a first set of electrodes at a first stage according to the sequence. The apparatus rotates the sequence to obtain a rotated sequence and applies one of the signals according to the rotated sequence. The apparatus receives sense signals to detect a presence of an object on the touch panel.