Layout Guidelines for SmartFusion2- and IGLOO2-Based Board Design
AC393 Application Note Revision 14.0 61
• t2: Post-cursor tap. The range is from -0.5 to -0.01, default value is -0.01.
• TapsFromFile: Explicit feed forward equalizer (FFE) coefficients can be set through this file. If a file
is used, it overrides the manual tap settings and automatic generation.
• TapsToFile: Output FFE tap coefficients to this file when automatic generation coefficients is used.
3.9.3.2 RX AMI Model
SerDes supports the programmable single pole continuous time linear equalization (CTLE) at the
receiver. The linear equalization comprises of amplifying higher frequency components that have been
more severely attenuated by the Interconnect, or attenuating the lower frequency components to a
greater degree than the higher frequency components.
The low-frequency attenuation level and the low-frequency flat-band bandwidth are programmable, as
shown in the following figure.
Figure 58 • Continuous Time Linear Equalization Response
Both ALF and ω
c
(f0) can be set to maximize the signal quality of the receiver for achieving the highest
possible bit error rate (BER).
• Alf: Low-frequency dB loss of the filter. The range is from 0 to 50, default value is 6.
• f0: High pass cut-off frequency. The range is from 1e
6
to 5e
10
, default value is 1e
9
.
3.9.4 Step 4: Results
Qualification of simulation results is done based on the eye-height, eye-width, and BER curves. Check
the eye-height and eye-width at target BER of 10e
-12
. These results are found in the report generated by
the simulation tool. For example, the Sigrity tool gives the following information at RX:
At BER of 10e
-12
, running at 5 Gbps bit rate
• The eye-width is 0.68 UI (Unit Interval)
• The eye-height is 213 mV
0 dB
A
LF
dB
Gain (dB)
Frequencyω
c
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