AD9877-EB datasheet(35/37 Pages) AD

35 / 37 page

AD9877

Rev. B | Page 34 of 36

SIGNAL ROUTING

The digital Rx and Tx signal paths should be kept as short as

possible. Also, these traces should have a controlled impedance

of about 50 Ω. This prevents poor signal integrity and the high

currents that can occur during undershoot or overshoot caused

by ringing. If the signal traces cannot be kept shorter than

approximately 1.5 inches, then series termination resistors

(33 Ω to 47 Ω) should be placed close to all signal sources. It is a

good idea to series terminate all clock signals at their source

regardless of trace length.

The receive (I IN, Q IN, and RF IN) signals are the most

sensitive signals on the board. Careful routing of these signals is

essential for good receive path performance. The Rx± signals

form a differential pair and should be routed together as a pair.

By keeping the traces adjacent to each other, noise coupled onto

the signals appears as common-mode and is largely rejected by

the MxFE receive input. Keeping the driving point impedance

of the receive signal low and placing any low-pass filtering of

the signals close to the MxFE further reduces the possibility of

noise corrupting these signals.

AD9877-EB Datasheet(PDF) 35 Page - Analog Devices