Micrel, Inc.

SY69753AL

August 2007

12

M9999-082107-E

hbwhelp@micrel.com or (408) 955-1690

Appendix A

Layout and General Suggestions

1.

Establish controlled impedance stripline, microstrip, or

coplanar construction techniques.

2.

Signal paths should have approximately the same width

as the device pads.

3.

All differential paths are critical timing paths, where

skew should be matched to within ±10ps.

4.

Signal trace impedance should not vary more than

±5%. If in doubt, perform TDR analysis of all high-speed

signal traces.

5.

Maintain compact filter networks as close to filter pins

as possible. Provide ground plane relief under filter path

to reduce stray capacitance. Be careful of crosstalk

coupling into the filter network.

6.

Maintain low jitter on the REFCLK input. Isolate the

XTAL oscillator from power supply noise by adequately

decoupling. Keep XTAL oscillator close to device, and

minimize capacitive coupling from adjacent signals.

7.

Higher speed operation may require use of

fundamental-tone (third-overtone typically has more

jitter) crystal-based oscillator for optimum performance.

Evaluate and compare candidates by measuring

TXCLK jitter.

8.

All unused outputs require termination. To conserve

power, unused PECL outputs can be terminated with a

1kΩ resistor to VEE.