LMH0344

SNLS233O – APRIL 2007 – REVISED JULY 2015

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10 Layout

10.1 Layout Guidelines

For information on layout and soldering of the WQFN package, please refer to the following application note: AN-

1187 Leadless Leadframe Package (LLP) (SNOA401).

The ST 424, 292, and 259 standards have stringent requirements for the input return loss of receivers, which

essentially specify how closely the input must resemble a 75-

Ω network. Any non-idealities in the network

between the BNC and the equalizer will degrade the input return loss. Take care to minimize impedance

discontinuities between the BNC and the equalizer to ensure that the characteristic impedance of this trace is 75

Ω.

Please consider the following PCB recommendations:

•

Use surface-mount components, and use the smallest components available. In addition, use the smallest

size component pads.

•

Select trace widths that minimize the impedance mismatch between the BNC and the equalizer.

•

Select a board stack up that supports both 75-

Ω single-ended traces and 100-Ω loosely-coupled differential

traces.

•

Place return loss components closest to the equalizer input pins.

•

Maintain symmetry on the complementary signals.

•

Route 100-

Ω traces uniformly (keep trace widths and trace spacing uniform along the trace).

•

Avoid sharp bends in the signal path; use 45° or radial bends.

•

Place bypass capacitors close to each power pin, and use the shortest path to connect equalizer power and

ground pins to the respective power or ground planes.

14

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