Checkpoint Systems Inc. EVOLVES10 Manual De Usuario
Chapter 1 – Universal Socket Connectivity
Multi-Tech Systems, Inc. Universal Socket Hardware Guide for Developers (S000342D)
14
Electromagnetic Interference (EMI) Considerations
The following guidelines are offered to specifically help minimize EMI generation. Some of these guidelines are
the same as, or similar to, the general guidelines but are mentioned again to reinforce their importance. In order
to minimize the contribution of the SocketModem-based design to EMI, the designer must understand the major
sources of EMI and how to reduce them to acceptable levels.
the same as, or similar to, the general guidelines but are mentioned again to reinforce their importance. In order
to minimize the contribution of the SocketModem-based design to EMI, the designer must understand the major
sources of EMI and how to reduce them to acceptable levels.
1.
Keep traces carrying high frequency signals as short as possible.
2.
Provide a good ground plane or grid. In some cases, a multilayer board may be required with full layers for
ground and power distribution.
ground and power distribution.
3.
Decouple power from ground with decoupling capacitors as close to the SocketModem module power pins
as possible.
as possible.
4.
Eliminate ground loops, which are unexpected current return paths to the power source and ground.
5.
Decouple the telephone line cables at the telephone line jacks. Typically, use a combination of series
inductors, common mode chokes, and shunt capacitors. Methods to decouple telephone lines are similar to
decoupling power lines; however, telephone line decoupling may be more difficult and deserves additional
attention. A commonly used design aid is to place footprints for these components and populate as
necessary during performance/EMI testing and certification.
inductors, common mode chokes, and shunt capacitors. Methods to decouple telephone lines are similar to
decoupling power lines; however, telephone line decoupling may be more difficult and deserves additional
attention. A commonly used design aid is to place footprints for these components and populate as
necessary during performance/EMI testing and certification.
6.
Decouple the power cord at the power cord interface with decoupling capacitors. Methods to decouple
power lines are similar to decoupling telephone lines.
power lines are similar to decoupling telephone lines.
7.
Locate high frequency circuits in a separate area to minimize capacitive coupling to other circuits.
8.
Locate cables and connectors so as to avoid coupling from high frequency circuits.
9.
Lay out the highest frequency signal traces next to the ground grid.
10.
If a multilayer board design is used, make no cuts in the ground or power planes and be sure the ground
plane covers all traces.
plane covers all traces.
11.
Minimize the number of through-hole connections on traces carrying high frequency signals.
12.
Avoid right angle turns on high frequency traces. Forty-five degree corners are good; however, radius turns
are better.
are better.
13.
On 2-layer boards with no ground grid, provide a shadow ground trace on the opposite side of the board to
traces carrying high frequency signals. This will be effective as a high frequency ground return if it is three
times the width of the signal traces.
traces carrying high frequency signals. This will be effective as a high frequency ground return if it is three
times the width of the signal traces.
14.
Distribute high frequency signals continuously on a single trace rather than several traces radiating from one
point.
point.
Handling Precautions
All electronic devices should be handled with certain precautions to avoid damage due to the accumulation of
static charge. Although input protection circuitry has been incorporated into the devices to minimize the effect of
this static buildup, proper precautions should be taken to avoid exposure to electrostatic discharge during
handling and mounting.
static charge. Although input protection circuitry has been incorporated into the devices to minimize the effect of
this static buildup, proper precautions should be taken to avoid exposure to electrostatic discharge during
handling and mounting.