ICS8432-101_07 Datasheet, PDF (13/20 Pages) Integrated Device Technology – 700MHZ, DIFFERENTIAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER

ICS8432-101
700MHZ, DIFFERENTIAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
The following component footprints are used in this layout
example: All the resistors and capacitors are size 0603.
POWER AND GROUNDING
Place the decoupling capacitors C14 and C15 as close as possible
to the power pins. If space allows, placing the decoupling capacitor
at the component side is preferred. This can reduce unwanted
inductance between the decoupling capacitor and the power pin
generated by the via.
Maximize the pad size of the power (ground) at the decoupling
capacitor. Maximize the number of vias between power (ground)
and the pads. This can reduce the inductance between the power
(ground) plane and the component power (ground) pins.
If V shares the same power supply with V , insert the RC filter
CCA
CC
R7, C11, and C16 in between. Place this RC filter as close to the
V as possible.
CCA
CLOCK TRACES AND TERMINATION
The component placements, locations and orientations should be
arranged to achieve the best clock signal quality. Poor clock signal
quality can degrade the system performance or cause system failure.
In the synchronous high-speed digital system, the clock signal is
less tolerable to poor signal quality than other signals. Any ringing
on the rising or falling edge or excessive ring back can cause system
failure. The trace shape and the trace delay might be restricted by
the available space on the board and the component location. While
routing the traces, the clock signal traces should be routed first and
should be locked prior to routing other signal traces.
• The traces with 50Ω transmission lines TL1 and TL2 at
FOUT and nFOUT should have equal delay and run ad-
jacent to each other. Avoid sharp angles on the clock trace.
Sharp angle turns cause the characteristic impedance to
change on the transmission lines.
• Keep the clock trace on same layer. Whenever possible,
avoid any vias on the clock traces. Any via on the trace
can affect the trace characteristic impedance and hence
degrade signal quality.
• To prevent cross talk, avoid routing other signal traces in
parallel with the clock traces. If running parallel traces is
unavoidable, allow more space between the clock trace
and the other signal trace.
• Make sure no other signal trace is routed between the
clock trace pair.
The matching termination resistors R1, R2, R3 and R4 should
be located as close to the receiver input pins as possible. Other
termination schemes can also be used but are not shown in this
example.
U1
PIN 1
C15
C14
C11
R7
C16
VCCA
TL1N
GND
VCC
VIA
Close to the input
pins of the
receiver
R4
R3
TL1
R2
TL1, TL2 are 50 Ohm traces and
equal length
R1
FIGURE 6B. PCB BOARD LAYOUT FOR ICS8432-101
IDT^™ / ICS^™ 700MHZ, 3.3V LVPECL FREQUENCY SYNTHESIZER
13
ICS8432DY-101 REV. C APRIL 10, 2007