Xilinx VC709 User Manual page 28

Chapter 1: VC709 Evaluation Board Features
GTH SMA Clock (SMA_MGT_REFCLK_P and SMA_MGT_REFCLK_N)
[Figure
The VC709 board includes a pair of SMA connectors for a GTH clock wired to GTH Quad
bank 113. This differential clock has signal names SMA_MGT_REFCLK_P and
SMA_REFCLK_N, which are connected to FPGA U1 pins AK8 and AK7 respectively.
Figure 1-10
•
•
X-Ref Target - Figure 1-10
Jitter-Attenuated Clock
[Figure
The VC709 board includes a Silicon Labs Si5324 jitter attenuator U24 on the back side of the
board. FPGA user logic can implement a clock recovery circuit and then output this clock
to a differential I/O pair on I/O bank 13 (REC_CLOCK_C_P, FPGA U1 pin AW32 and
REC_CLOCK_C_N, FPGA U1 pin AW33) for jitter attenuation. The jitter-attenuated clock
(Si5324_OUT_C_P, Si5324_OUT_C_N) is then routed as a reference clock to GTH Quad 113
inputs MGTREFCLK0P (FPGA U1 pin AH8) and MGTREFCLK0N (FPGA U1 pin AH7).
The primary purpose of this clock is to support CPRI/OBSAI applications that perform
clock recovery from a user-supplied SFP/SFP+ module and use the jitter-attenuated
recovered clock to drive the reference clock inputs of a GTH transceiver. The
jitter-attenuated clock circuit is shown in
28
1-2, callout 8]
shows this AC-coupled clock circuit.
External user-provided GTH reference clock on SMA input connectors
1.8V differential input
J25
SMA_MGT_REFCLK_C_P
SMA
Connector
J26 GND
SMA_MGT_REFCLK_C_N
SMA
Connector
GND
Figure 1-10: GTH SMA Clock Source
1-2, callout 9]
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C25
SMA_MGT_REFCLK_P
0.01 μF 25V
X7R
C24
SMA_MGT_REFCLK_N
0.01 μF 25V
X7R
Figure 1-11.
VC709 Evaluation Board
UG887 (v1.0) February 4, 2013
UG887_c1_10_090612