Hangzhou Xuhong Technology Co.,Ltd
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Projective capacitive touch screen can accurately locate the position of the finger touching the screen. It can identify the finger position by measuring the tiny change of capacitance. In such touchscreen applications, one of the key design issues to be considered is the impact of electromagnetic interference (EMI) on system performance. Performance degradation caused by interference may adversely affect the design of touch screen.
A typical projective capacitive sensor is installed under a glass or plastic cover plate. The transmitting (Tx) and receiving (Rx) electrodes are connected to transparent indium tin oxide (ITO) to form a cross matrix. Each Tx-Rx node has a characteristic capacitance. Tx ITO is located below Rx ITO and is separated by a layer of polymer film or optical adhesive (OCA).
To analyze the work of the touch screen: the operator's finger is at the nominal ground potential. Rx is maintained at the ground potential through the touch screen controller circuit, while Tx voltage is variable. The varying Tx voltage causes the current to pass through the Tx-Rx capacitance. A carefully balanced Rx integrated circuit isolates and measures the charge entering Rx. The measured charge represents the "mutual capacitance" connecting Tx and Rx.
Projective capacitive touch screens, which are widely used in portable devices today, are vulnerable to electromagnetic interference. Interference voltage from inside or outside will be coupled to touch screen devices through capacitance. These interference voltages will cause charge movement in the touch screen, which may cause confusion in charge movement measurement when fingers touch the screen. Therefore, the effective design and optimization of the touch screen system depends on the understanding of the interference coupling path and its reduction or compensation as much as possible.
The interference coupling path involves parasitic effects, such as transformer winding capacitance and finger - device capacitance. Proper modeling of these impacts can fully recognize the source and size of interference.
For many portable devices, battery chargers constitute the main interference source of touch screen. When the operator's fingers touch the touch screen, the generated capacitance makes the charger interference coupling circuit closed. The quality of the internal shield design of the charger and whether there is an appropriate grounding design of the charger are the key factors affecting the interference coupling of the charger.
AUO LCD:https://www.auo-lcd.com/products/auo-lcd-screen/
TFT LCD:http://www.auo-lcd.com
