GS3471 datasheet(174/179 Pages) SEMTECH

174 / 179 page

GS3471

Final Data Sheet Rev.4

PDS-060498

September 2017

174 of 179

Semtech

www.semtech.com

6.2 Layout Considerations

General best practices for high-speed board layout should be followed when designing

with the GS3471. These general best practices can be found in a number of Semtech

design guides including:

•

GS3471 Receiver Design Guide (TBD)

•

GS2972 Transmitter Design Guide (GENDOC-048581)

•

Multi-Gigabit Serial Routing Products (PDS-060967)

•

GS2989 Cable Driver Design Guide (GENDOC-052070)or most recent CD design

guide available

The following layout considerations are specific to the GS3471:

•

GS3471's analog supplies, particularly its 1.2V VCC supply, are sensitive to noise. For

optimal performance, it is recommended that the power supplies are isolated to

avoid external noise coupling. DDI_VDD and DDO_VDD may be combined if they

are powered at the same supply level. However, PLL_VDD, CORE_VDD and

IO_VDD should be routed separately.

•

Linearly regulated power supplies are recommended wherever possible as they

provide the cleanest power.

•

Critical components such as power supply decoupling capacitors, LF capacitor,

RBIAS resistor, CT0 and CT1 capacitors and VCO filter should be placed as close as

possible to the GS3471.

•

DDI/DDI, SDI/SDI, and DDO/DDO differential inputs and outputs should be routed

using 100Ω differential controlled impedance transmission lines.

•

When paired with a compatible cable equalizer or cable driver, it is possible to

DC-couple the differential high-speed inputs and outputs. In cases requiring

AC-coupling, anti-pads should be used underneath AC-coupling capacitors to

minimize the parasitic capacitance associated with these components. Details on

the use of anti-pads can be found in the Semtech video design guides referenced

above.

•

The parallel data outputs and timing signals should be electrically phase matched

to within 1/20th of a wavelength. For 300MHz, this is approximately equivalent to

1" of FR4 micro-strip.

•

Serial termination on the parallel data outputs and timing signals may be required

for very long traces or traces going through connectors.

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