Passive Filtering; Figure 4-7: Power Filtering Network For One Transceiver - Xilinx RocketIO User Manual

R
for the adjustable version of the LT1963 device with values for a 2.5 V supply, as would be
used for AVCCAUXRX and AVCCAUXTX. Alternatively, fixed output voltage devices in
the same series may be used, such as the LT1963-2.5. If the fixed version is used, SENSE
should be connected to OUT.
Termination voltages V
In cases where the RocketIO transceiver is interfacing with a transceiver from another
vendor, termination voltage may be dictated by the specifications of the other transceiver.
In cases where the RocketIO transceiver is interfacing with another RocketIO transceiver,
any termination voltage my be used. The logical choice is 2.5 V, as this voltage is already
available on the board for the AVCCAUXTX and AVCCAUXRX supplies.
The LT1963 circuit's output capacitors (100 µF and 1 µF) may be placed anywhere on the
board, preferably close to the output of the LT1963 device.
Refer to the manufacturer's Web page at
information about this device.

Passive Filtering

To achieve the necessary isolation from high-frequency power supply noise, passive filter
networks are required on the power supply pins. The topology of these capacitor and
ferrite bead circuits is given in
Each transceiver power pin requires one capacitor and one ferrite bead. The capacitors
must be of value 0.22 µF in an 0603 SMT package of X7R dielectric material at 10%
tolerance, rated to at least 5 V. These capacitors must be placed within 1 cm of the pins they
are connected to. The ferrite bead is the Murata BLM18AG102SN1. These components may
not be shared under any circumstances.
Figure 4-8
transceivers. The device is in an FF672 package, which has eight transceivers total—four
on the top edge and four on the bottom edge.
lands for the capacitors and ferrite beads of the VTTX and VTRX supplies. The ferrite
beads are L1, L2, L3, L4, L9, L11, L12, and L21; the capacitors are C85, C90, C94, C96, C98,
C100, C119, and C124.
and ferrite beads of the AVCCAUXTX and AVCCAUXRX supplies. The ferrite beads are
L10, L13, L15, L16, L19, L33, and L34; the capacitors are C141, C144, C211, C221, C223,
C225, C227, and C229.
90
and V
TTX TRX
Figure
2.5V
BLM18AG102SN1
BLM18AG102SN1
V
TT
BLM18AG102SN1
V
TR
BLM18AG102SN1

Figure 4-7: Power Filtering Network for One Transceiver

and Figure 4-9 show an example layout of the power filtering network for four
Figure 4-9 shows the bottom PCB layer, with lands for the capacitors
www.xilinx.com
1-800-255-7778
Chapter 4: Analog Design Considerations
may be of any value in the range of 1.8 V to 2.625 V.
http://www.linear-tech.com
4-7.
AVCCAUXRX
0.22µF
AVCCAUXTX
0.22µF
VTTX
0.22µF
VTRX
0.22µF
GNDA
UG024_20_022002
Figure 4-8 shows the top PCB layer, with
UG024 (v1.5) October 16, 2002
RocketIO™ Transceiver User Guide
for further