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DESIGN CONSIDERATIONS

Design Considerations

USB Design

Multi-Tech recommends that you review Intel's High Speed USB Platform Design Guidelines for information about

USB signal routing, impedance, and layer stacking. Also:

■ Shield USB cables with twisted pairs (especially those containing D+/D-).

■ Use a single 5V power supply for USB devices. See the Power Draw section in your model’s Device Guide for

current (ampere) requirements.

■ Route D+/D- together in parallel with the trace spacing needed to achieve 90 ohms differential impedance

for the USB pair and to maintain a 20 mil space from the USB pair and all other signals.

■ If power is provided externally, use a common ground between the carrier board and the device.

Noise Suppression Design

Adhere to engineering noise-suppression practices when designing a printed circuit board (PCB) containing the

MultiConnect PCIe. Noise suppression is essential to the proper operation and performance of the modem and

surrounding equipment.

Any OEM board design that contains the MultiConnect PCIe must consider both on-board and off-board generated

noise that can affect digital signal processing. Both on-board and off-board generated noise that is coupled on-

board can affect interface signal levels and quality. Noise in frequency ranges that affect modem performance is of

particular concern.

On-board generated electromagnetic interference (EMI) noise that can be radiated or conducted off-board is

equally important. This type of noise can affect the operation of surrounding equipment. Most local government

agencies have certification requirements that must be met for use in specific environments.

Proper PC board layout (component placement, signal routing, trace thickness and geometry, and so on)

component selection (composition, value, and tolerance), interface connections, and shielding are required for the

board design to achieve desired modem performance and to attain EMI certification.

Other aspects of proper noise-suppression engineering practices are beyond the scope of this guide. Consult noise

suppression techniques described in technical publications and journals, electronics and electrical engineering text

books, and component supplier application notes.

Electromagnetic Interference

The following guidelines are offered specifically to help minimize EMI generation. Some of these guidelines are the

same as, or similar to, the general guidelines. To minimize the contribution of device-based design to EMI, you

must understand the major sources of EMI and how to reduce them to acceptable levels.

■ Keep traces carrying high frequency signals as short as possible.

■ Provide a good ground plane or grid. In some cases, a multilayer board may be required with full layers for

ground and power distribution.

■ Decouple power from ground with decoupling capacitors as close to the device's power pins as possible.

■ Eliminate ground loops, which are unexpected current return paths to the power source and ground.

6 QuickCarrier™ USB-E MT100UCC-C2 Developer Guide

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