SFP + High-Speed Channel Performance Simulation And Measure
Pan Jiang
1
, Runjing Zhou
2
, Jialu Zhou
3
Department of Automation
College of Electronic Information Engineering
Inner Mongolia University
Hohhot, China
E-mail: scandalsoul@163.com
1
; auzhourj@163.com
2
; imuzhoujl@163.com
3
Abstract—The 10Gbps high-speed serial interface has been
used in data transmission widely. As the bandwidth
demanding for high-speed communication network sharply
increases, it is increasingly important to investigate the
interconnection of high-speed serial interface. In this paper,
the SFP+ interface signal integrity(SI) were analyzed with
EM simulation and the lab measurement. The 2.5D and 3D
modeling methodologies were introduced for the interest
transmission line in the frequency domain. We measured its
differential mode (DM) reflection and transmission
coefficients, subsequently observed the variation of DM
impedance and analyzed the causes of impedance
discontinuity by the utilization of TDR measurement, and
finally put forward several methods to improve the SI. It is
notable that the simulation results of the 2.5D and 3D model
are almost identical by comparison, which means that 2.5D
modeling methodologies also can achieve high accuracy
around 10Ghz. Additionally, we optimized the SI simulation
results by varying the output voltage and pre-emphasis
parameters. Finally, the SFP+ compliance test shows the
simulation has good agreement with lab measurement in the
time domain.
Keywords—SFP+ interface; 2.5D model; 3d model; SI
simulation; the differential transmission
I. INTRODUCTION
With the increases of bandwidth demanding of data
communication, more and more high-speed serial
interfaces gradually are replacing the traditional parallel
interfaces. There are many popular high-speed serial
interfaces in using like PCIe,USB3.0,SFP+,etc.Their
maximum data rates are showed in the Table1[1].
Especially, the SFP+ interface has become the mainstream
of 10Gbps high-speed channel, which has the advantages
of small volume and low cost [2]. The SFP+ is the
pluggable serial receivers, it’s module can be divided into
two types, limiting and linear. The SFP+ module does not
need to integrate the clock and data recovery (CDR) and
SerDes in the module, which is moved to the host ASICs
where the cost of electronics is lower and higher
integration is feasible [3]. In general, when the signal
transmission rate is more than 5Gbps, a CDR with
advanced electronic dispersion compensation technology
on the receive (Rx) path and a CDR with pre-emphasis,
slew rate and output amplitude adjustments on the
transmit (Tx) path should be required . Despite the
technology breakthrough of fibre-optic over traditional
wiring communications, there is still in need for
converting optical signal into electrical signal to feed in
frontend of server computer for further processing[4], so
high-speed connectors now become the most critical
factor for signal integrity requirements[5].
TABLE1 HIGH-SPEED SERIAL INTERFACE DATA RATE TRENDS
The evaluation board was used to validate the 10Gbps
channel modeling SI simulation flow, as shown in Fig1.
This board is based on Altera StratixV GX with
5SGXEA7N2F40C2N FPGA chip, which has one
12.5Gbps SFP+TX/RX channel.
Fig1. StratixV GX SI Evaluation Board
II. FREQ-DOMAIN CHANNEL MODELING
Generally, before checking the waveform in the time
domain, the model of interest object should be introduced
in the frequency domain. The PCB was fabricated by FR4
material with 20 layers, it’s thickness was 3.5mm. The
interest SFP+ TX signals were routed as microstrip lines
in the top layer and bottom layer with a via stub. The
length of line was about 3inch.
The differential pair transmission was applied to SFP+
connector, the 2.5D and 3D modeling methodologies were
introduced for the interest microstrip lines in the
frequency domain to get S-param model accurately. The
3D modeling was introduced by HFSS software, as shown
in Fig2a,Fig2b. The 2.5D modeling was introduced by
SIwave software .Undoubtedly, HFSS has been the
industry standard of simulation because of the most
978-1-4799-0641-3/13/$31.00: copyright: 2013 IEEE