PDS-060930 Rev.0 December 2014
GX3246
IBIS-AMI Model
User Guide (First Draft)
PDS-060930 Rev.0 December 2014
1. Introduction
The GX3246 is a low-power, high-speed 290×146 crosspoint switch, with robust signal conditioning
circuits for driving and receiving high-speed signals through backplanes. This document describes the
contents, features, and use of the GX3246 IBIS-AMI model. The model includes all equalization, de-
emphasis and swing settings of the GX3246 and facilitates simulation of the GX3246 in EDA platforms
compliant with IBIS 5.0.
2. GX3246 IBIS-AMI Model
The GX3246 IBIS-AMI model comprises of RX and TX models. The RX model applies the equalization
on signal received from a channel. The received signal is then transmitted into another channel using the
TX model. Note that the switching core is not included in the model. Therefore, the RX and TX models
have to be used in two separate testbenches to optimize the chip different settings and board design as
shown in Figure 2-1.
Figure 2-1: The receiver and transmitter testbenches in order to use GX3246 IBIS-AMI model.
Please be advised that the receiver output signal represents the signal at the output of the on-chip equalizer
and the transmitter input is the signal after the switching core. In order to meet the receiver sensitivity
specifications, the signals at the equalizer output should have more than 100mVppd vertical eye opening.
The user should optimize the equalizer output to have the maximum vertical and horizontal eye opening.
Please note that this eye diagram will be sliced before going into the switching core and its shape is not
very important as long as it has low jitter and high vertical eye opening. The slicers have not been included
in the receiver model in order to build a linear model.
2.1 GX3246 Receiver IBIS-AMI Model
The GX3246 Receiver IBIS-AMI model consists of three parts: (1) the Analog Termination IBIS model,
(2) the Receiver AMI model and (3) the QFN package model. The block diagram in Figure 2-2 shows the
sequence of signal flow and the individual parts of the model. The external S-parameter file for the QFN
Package model extends the accuracy of the package effects beyond which can be described by R, L and C
components in the current IBIS 5.0 standard. The external S-parameter data is processed as part of the
channel by the EDA platforms.
PDS-060930 Rev.0 December 2014
Figure 2-2: GX3246 Receiver IBIS-AMI Model
2.1.1 GX3246 Receiver IBIS Model
The receiver IBIS model provides the characterized GX3246 Receiver input termination which is used by
the EDA platform to determine the time-domain impulse response for the channel. The model is based on a
single-ended non-inverting characterization of the GX3246 Receiver and the EDA platform develops a
differential model from complimentary copies of the single-ended model. Two different sub-models have
been employed for different termination modes. The appropriate sub-model has to be selected based on
EQ_termination parameter in the datasheet (page 21). Table 2-1 summarizes the use of GX3246 receiver
sub-models.
Table 2-1: Receiver sub-model selection based on EQ_termination parameter.
EQ_Termination
Input Termination Common Mode Point
Switch to VCC_IN1, VCC_IN_2
Sub-Model
Termination
0
Open (Figure3-1 in datasheet)
Sdi_pd0_cm25
Differential
1
Closed (Figure3-1 in datasheet)
Sdi_pd0_cm12
Single-Ended
Note that the IBIS model only contains the DC termination impedance of the receiver (I-V tables in IBIS
file) and doing frequency dependent simulations (e.g. return loss simulations) using the IBIS file is not very
accurate. It is recommended to use “GX3246_RX_Term.s2p” S-parameter file instead of the IBIS file in
order to do input return loss (IRL) simulations.
2.1.2 GX3246 Receiver AMI Model
The GX3246 Receiver model features adjustable trace equalization for PCB trace dielectric losses up to
half the maximum supported data rate, or 1.5GHz. The equalization setting can be adjusted by the
following model specific parameter:
EQ_Boost: The equalization has four different settings to compensate from 0 to 47 inches (119 cm) of FR4
trace at 3Gb/s. The boost at the 1.5GHz Nyquist frequency, and recommended trace length range, is shown
in Table 2-1.
Table 2-2: EQ_Boost parameter in the receiver AMI model.
EQ_Boost
Boost Applied @ 1.5GHz
Recommended Trace Length
0
0dB
0” to 6” (15cm)
1
3.5dB
6” (15cm) to 16” (40cm)
2
7.6dB
16” (40cm) to 35” (89cm)
PDS-060930 Rev.0 December 2014
3
12dB
35” (89cm) to 47” (119cm)
2.1.3 GX3246 Receiver Package Model
The GX3246 FCBGA package model is provided as a 4-Port S-parameter file (GX3246_RX_Pkg.s4p) in
standard touchstone format from 0 to 20 GHz with 2001 data points. This model has been developed for
one pair of differential input pins and the package model for the rest of input pins may be slightly different
from this model.
2.2 GX3246 Transmitter IBIS-AMI Model
The GX3246 Transmitter IBIS-AMI model consists of three parts: (1) the Analog Driver IBIS model, (2)
the Transmitter AMI model, and (3) the QFN package model. The block diagram in Figure 2-3 shows the
sequence of the signal flow and the individual parts of the model.
Figure 2-3: GX3246 Transmitter IBIS-AMI Model
2.2.1 GX3246 Analog Driver IBIS Model
The Analog Driver IBIS model receives processed signal information from the Transmitter AMI model and
applies the analog characteristics of the GX3246 Transmit driver. The model is based on a single-ended
non-inverting characterization of the GX3246 Receiver and the EDA platform develops a differential
model from complimentary copies of the single-ended model. Eight different sub-models have been
employed for different output swing settings. The appropriate sub-model has to be selected based on the
transmitter output swing and supply voltage. Table 2-3 summarizes the use of GX3246 receiver sub-
models.
Table 2-3: Transmitter sub-model selection based on the output swing and power supply.
Supply Voltage (V)
Output Swing (mVppd)
Sub-Model
1.2/1.8
200
Sdo_12_000
1.2/1.8
400
Sdo_12_001
1.2/1.8
800
Sdo_12_011
2.5
200
Sdo_25_000
2.5
400
Sdo_25_001
2.5
800
Sdo_25_011
2.5
1200
Sdo_25_110
PDS-060930 Rev.0 December 2014
2.5
1600
Sdo_25_111
Note that the IBIS model only contains the DC termination impedance of the receiver (I-V tables in IBIS
file) and doing frequency dependent simulations (e.g. return loss simulations) using the IBIS file is not very
accurate. It is recommended to use “GX3246_TX_Term.s2p” S-parameter file instead of the IBIS file in
order to do output return loss (ORL) simulations.
2.2.2 GX3246 Transmitter AMI Model
The GX3246 Transmitter AMI model consists of different de-emphasis settings which can be adjusted by a
model specific parameter. These parameters are described in the following. Note that these parameters are
the same as the registers in the datasheet. It is highly recommended that the user study the datasheet of
GX3246 and the register descriptions carefully before using the model.
1. Output_DeEmphasis: Selects the output de-emphasis level.
Table 2-4: Output_DeEmphasis in Transmitter AMI model.
Output_DeEmphasis
Register Value
Level of De-emphasis
0
000
Off
1
100
12” (30 cm) nominal
2
101
24” (60 cm) nominal
3
110
36” (90 cm) nominal
4
111
48” (120 cm) nominal
2. Active_Signal_Invert: Inverts the polarity of the signal when it is set to 1.
2.2.3 GX3246 Transmitter Package Model
The GX3246 FCBGA package model is provided as a 4-Port S-parameter file (GX3246_TX_Pkg.s4p) in
standard touchstone format from 0 to 20GHz with 2001 data points. This model has been developed for one
pair of differential output pins and the package model for the rest of output pins may be slightly different
from this model.
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