Altera Early SSN Estimator - Manual (Page 5)

© November 2009 Altera Corporation Early SSN Estimator User Guide for Altera Programmable Devices
1. Early SSN Estimator
Use the early SSN estimator (ESE) to estimate the simultaneous switching noise (SSN)
in your designs during the early design phase. This avoids going through extensive
pre- and post-layout simulations. The early SSN estimator is a Microsoft Excel-based
spreadsheet tool for calculating the worst-case quiet low/quiet high noise seen at the
far end of the victim pin induced by multiple aggressors switching simultaneously.
The early SSN calculator assumes typical process, voltage, and temperature (PVT)
conditions for the targeted device and the PCB board under development. The
spreadsheet requires only basic design-specific information such as the I/O standard,
current strength, slew rate, and number of simultaneous switching I/Os.
1 The early SSN estimator models the SSN generated by inductive crosstalk. Current
draw of the switching buffers may create power delivery network (PDN) resonance
and cause PDN compression. PDN compression due to resonance is different from the
SSN described here. Improving PDN design reduces PDN compression.
The results obtained through the spreadsheet tool are intended only as an estimate of
the worst case noise and not as a specification. The actual results observed on your
board may vary due to differences between your PCB design and the assumed typical
design conditions used by the calculator. For designers who intend to get a very
accurate noise estimate based on their specific PCB design, Altera recommends using
a post-layout simulation approach, taking into account the various parameters such
as board stackup, via breakout, power delivery network design, and trace spacing
specific to the design.
This user guide describes how to use the early SSN estimator to estimate the far-end
noise induced on the victim pin.
Application of the Tool
The purpose of the tool is to provide a rough estimate on the amount of SSN within
the design during the early design phase. This spreadsheet tool is very useful when
exploring the various “what-if” scenarios to study the impact on the observed noise
seen using different drive strengths, various number of simultaneous switching I/Os,
different VCCIO voltage standards, and various I/O settings.
Setting up the Early SSN Estimator
The ESE spreadsheet consists of the following tabs ( Figure 1–1 ):
■ Calculator —the primary tab where you input the relevant design information to
estimate the amount of SSN noise.
■ Data Viewer —gives a schematic view of the noise profile of individual I/O
standards as a function of the number of I/Os. The Data Viewer tab is independent
of the Calculator tab. It only displays the noise profile of the I/O standard that is
set in the Data Viewer tab regardless of the I/O standards selected for the various
banks in the Calculator tab.