In-Cell Touch Controller Waveforms for Low-Emission Sensing
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Solution Overview
Problem
Existing touch-sensing technologies, such as multiphase self-capacitance and floating ground methods, face challenges in achieving high sensitivity and noise rejection, especially in in-cell touch controllers for automotive applications with strict emission requirements, due to high panel capacitance and sensitivity to external noise.
Innovation Solution
The implementation of a windowed sinusoidal waveform and custom transition waveform between display and sensing functions, combined with a signal generator using a multi-level sigma-delta modulator and phase adjustments of sense channel signals, reduces emissions and improves signal-to-noise ratio (SNR) for capacitive sensing in in-cell touch displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional multiphase self-capacitance or floating ground methods are used, then touch sensing functionality is achieved, but emissions are high and sensitivity is insufficient
Solution Approach 1:
The patent implements separate display function intervals and touch scanning intervals with periodic switching between them. During display intervals, display signals are driven; during scanning intervals, touch sensing is performed. This periodic separation prevents simultaneous emission of display signals and radiated emissions from sensing, thereby reducing overall radiated emissions while maintaining reliable touch detection through dedicated scanning periods
Solution Approach 2:
The patent applies a windowed sinusoidal waveform to the sense electrode before actual touch scanning begins. This preliminary excitation signal with smooth envelope (windowing function) prepares the sensing circuit and reduces transient emissions compared to abrupt signal switching, while the sinusoidal nature provides stable frequency reference for accurate capacitive measurement, improving both emission reduction and sensing reliability
2Measurement precision
If high excitation energy is used to improve signal-to-noise ratio, then sensing sensitivity improves, but emissions increase
Solution Approach 1:
The patent concentrates excitation energy into dedicated touch scanning intervals rather than continuous excitation. During these periodic scanning intervals, high-energy sinusoidal excitation signals are applied to achieve sufficient signal-to-noise ratio for accurate capacitive measurement. Between scanning intervals, during display periods, excitation is minimized or stopped, reducing overall radiated emissions while maintaining measurement precision when needed
Solution Approach 2:
The patent dynamically adjusts the excitation signal characteristics by using windowed sinusoidal waveforms with variable envelope functions. The windowing allows smooth amplitude modulation of the excitation signal, concentrating energy where needed for sensing while reducing energy during transitions and idle periods. This dynamic control optimizes the balance between achieving sufficient excitation energy for good signal-to-noise ratio and minimizing overall emissions
Data Source
AI summary
Technology directed to low-emissions touch controller in in-cell touch display systems is described. One in-cell touch controller includes a signal generator circuit that is configured to generate a sense signal according to a sensing function, the sense signal including a windowed sinusoidal waveform. The controller generates a transition signal to transition the in-cell touch display between a display function and the sensing function. The controller drives the sense signal and the transition signal on common voltage (VCOM) layer of electrodes during a touch scanning interval. During a display function interval an integrated display driver is configured to drive a first signal on the VCOM layer of electrodes during a display function interval.