Touch screen of electromagnetic interference problem

Touch screen often electromagnetic interference problem, hu and also what the solution? Charger is another potential source of interference touch screen interference power supply switch power supply of mobile phone chargers. Interfere with the coupling through the fingers to touch screen, as shown in figure 

5. Small mobile phone charger usually have the ac power line and zero line input, but no ground connection. The charger is security isolation, so the power input and the charger no dc connection between secondary coil. This, however, will still be generated by switching power supply isolation transformer capacitive coupling. The charger interference by finger touch screen to form a return path. Note: in this case, the charger interference refers to the applied voltage equipment relative to the ground. 

 This kind of interference may be due to its equivalent on the dc power supply and dc ground and was described as 'common mode' interference. In the charger output dc to dc power supply and power switch between the noise, if have not been fully filter, may affect the normal operation of the touch screen.

 The power supply rejection ratio ( PSRR) Problem is another problem, do not discuss in this paper. The charger coupled impedance through the transformer primary - charger switch interference The secondary winding leakage capacity ( About 20 pf) Coupling. 

 The weak current capacity coupling can be appear in the charger cable and from electric equipment itself relatively distributed parasitic shunt capacitance compensation. Pick up the equipment, the shunt capacitance will increase, this is usually enough to eliminate the charger switches interference, avoid the disturbance affects a touch. As portable devices connected to the charger and on the desktop, and operator's finger only contact with the touch screen, there will be a worst-case interference produced charger.
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