EMC Design Guide for Printed Circuit Boards
Frame 64 of 78
Printed copies are uncontrolled
5.4. Analog Circuits
59. Analog or peripheral circuitry should be located as close to the I/O connector as
possible, and be kept away from high speed digital, high current, or power switching
circuits. Figure 52.
60. Routing of low level analog signals should be confined to analog section of PCB
61. Low pass filtering should always be used on all analog inputs.
62. Printed circuit board traces which terminate at the device connector should be
decoupled of RF at the connector.
63. Ground guard tracks should always be routed adjacent to analog signals. Attach the
guard tracks at both ends with vias to sending and receiving circuits' ground.
64. If using suppression device across coils of relays and/or solenoids the suppressor
should be placed as close to the coil terminals as possible.
65. If a PWM signal is used to drive a solenoid, resistor suppression may be used. This
will prevent high rate of change of current (di/dt), which can cause excessive
magnetic field radiation.
66. Biasing resistors when placed as close as physically possible to the base of transistors
may prevent RF from coupling in and turning the transistor on or off. (Figure 517)
67. Base and emitter bypass capacitors should be located very close to transistors (Figure
517). They should be connected to ground with low impedance connection to
minimize inductance and loop area.
Figure 517. Transistor Circuit Routing
68. Treat every trace carrying sensitive signals (especially into high input impedance
loads i.e. higher than 10 k) as a receiving antenna when considering its routing.