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PCB Design Rules for Sensitive Circuits to avoid EMI problems

PCB designing is usually done on the very popular E-CAD software called OrCAD. Imagine a circuit like that of Ethernet kit using ENC28J60 that has different voltage level such as Low-voltage (3.3V), TTL/CMOS voltage level (5V) and the LAN standard signals levels. It also has the high frequency signals of SPI interface with clock of 10MHz and the LAN standard signals with modulation rate of 20MHz. All these signals may interfere with each other if the tracks of the PCB are not properly routed and the components are not placed to appropriate location due to EMI, this interference may cause the malfunctioning of the circuit. Some rules should be followed to avoid the EMI problems
  • Keep the tracks length as short as possible
  •  Do not route the analog signal and the digital signal together
  •  Keep the clock track separate from the other signal
  • Keep the high frequency signals tracks separate from the other signals.
  • Keep the Ground track as short as possible.
  • Keep the lengths of the connector short of high frequency signals such as SPI clock (!important)
  •  Do not turn the route at 90o.
  •  Never run the clock signal tracks to outer edge of the PCB
  • No unrelated component should be closer than 1 inch to the crystal
  • Put the crystal not farther than 1 cm form oscillator pin
  • Put RBIAS resistor as close as possible to pin.

Posted by Muhammad Ahmed on 16:22. Filed under , , . You can follow any responses to this entry through the RSS 2.0. Feel free to leave a response

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