38-640MHz Low Phase Noise XO
47745 Fremont Blvd., Fremont, California 94538 Tel (510) 492-0990 Fax (510) 492-0991 www.phaselink.com Rev 11/14/07 Page 8
LAYOUT RECOMMENDATIONS
PCB LAYOUT CONSIDERATIONS FOR PERFORMANCE OPTIMIZATION
The following guidelines are to assist you with a performance optimized PCB design:
- Keep all the PCB traces to PL680 as short as
possible, as well as keeping all other traces as
far away from it as possible.
- Place the crystal as close as possible to both
crystal pins of the device. This will reduce the
cross-talk between the crystal and the other
signals.
- Separate crystal pin traces from the other signals
on the PCB, but allow ample distance between
the two crystal pin traces.
- Place a 0.01µF~0.1µF decoupling capacitor
between VDD and GND, on the component side
of the PCB, close to the VDD pin. It is not
recommended to place this component on the
backside of the PCB. Going through vias will
reduce the signal integrity, causing additional
jitter and phase noise.
- It is highly recommended to keep the VDD and
GND traces as short as possible.
- When connecting long traces (> 1 inch) to a
CMOS output, it is important to design the traces
as a transmission line or ‘stripline’, to avoid
reflections or ringing. In this case, the CMOS
output needs to be matched to the trace
impedance. Usually ‘striplines’ are designed for
50Ω impedance and CMOS outputs usually have
lower than 50Ω impedance so matching can be
achieved by adding a resistor in series with the
CMOS output pin to the ‘stripline’ trace.
- Please contact PhaseLink for the application note
on how to design outputs driving long traces or
the Gerber files for the PL680 layout.
