Design And Analysis Of In-cell Capacitive Touch Sensor

As the most direct human-computer interface,touch screen performance is decisive for user experience.Based on different principles,touchscreen can be designed in different ways.Current handheld touch screen devices are mainly using capacitive touch technology.Touch sensor design can be divided into two kinds,i.e.discrete and embedded.As a standalone component,discrete touchscreen is assembled by lamination technology.Abandoning the discrete touch sensor,In-Cell sensor can be directly integrated into the LCD.In-Cell design eliminates the need for a separate touch module,not only reduces system cost,leaves more space for the battery but also able to further optimize the touch and display performance.This paper is about sensor design and analysis of In-Cell capacitive touchscreen.The content includes the following aspects: In-Cell touch sensor design,touch signal processing,and touchscreen performance verification.The design principle of In-Cell sensor is analyzed at the beginning.The touch platform is built with Synaptics' S3320 touch controller IC,R6345 X display driver IC and IPS displayer.The VCOM electrode in the display is segmented into the stripes which are share used as touch sensor's transmitter electrode,and the fork shaped electrode that arranged on the display color filter glass are acting as the receiver electrode.In order to further determine the pitch parameter of the sensor receiver electrode,this paper uses COMSOL Multiphysics to perform the finite element analysis.By calculating the influence of the pitch parameter on the mutual capacitance and SNR,and by simulating the influence of different size of fingers on the specific sensor,combining with the general touch application,the reasonable range of the sensor receiver electrode pitch setting is determined.For sensor signal acquisition and processing,this paper studied the touch and display synchronization mechanism,touch operation can be done during the blank time of displayer.The application of interpolation method in touch coordinates positioning is also studied in this paper.Based on the results of finite element model,the application limits of several positioning algorithms are analyzed,and the conclusion that for different application scenarios positioning algorithms can be chosen respectively was drawn.Based on the performance requirements,this paper studied some specific test items and gave test results by demo board test.