RGB classification of LCD display EMI problems and solutions of RGB screen part two

Four EMI solution recommendations

1. Add RC filtering or magnetic beads and capacitor filtering to DCLK (the parameter size needs to be determined by referring to the clock size); the cutoff frequency of the filter 1/πtr is greater than or 10 times the clock frequency, set a resistance value, according to f0 =1/2πRc can obtain the filter capacitor parameters, and the filter should be placed as close to the connector as possible. 2. Add RC filtering or magnetic beads and capacitor filtering to the RGB signal, or add magnetic rows and resistors; because there will be clock interference on the RGB signal, it needs to be filtered.

3. Board modification suggestion: Ground-cover the CLK clock trace; the clock energy of the RGB signal is relatively high, to avoid clock noise from interfering with other signal lines, the clock trace can be ground-wrapped, which can also make the clock more efficient. With a good return path, the high-frequency loop area is minimized. Things to note when covering the ground: The width of the ground line is equal to the width of the clock line; the spacing between ground vias is 1/20 of the signal wavelength, and the signal wavelength is the actual frequency of the noise.

4. Interference on FPC cables; Wire harnesses with poor shielding or no shielding effect will cause radiation to exceed the standard. A magnetic ring can be added for verification, and the cables should be shielded and grounded.

5. A spread spectrum IC can be added to the clock or a spread spectrum crystal oscillator can be added to the main clock. The appropriate spread spectrum IC can be selected according to the clock frequency.

Five summary

RGB TFT LCD screens are a troublesome issue, especially the clock issue. Issues that must be considered when designing the PCB board in the early stage, such as port placement, wiring design, reserved device locations, etc., can reduce many detours for engineers. , face the source of the problem, and control it in the cradle, so that engineers can move towards the bright road of EMC.