DS32ELX0421SQX/NOPB National Semiconductor, DS32ELX0421SQX/NOPB Datasheet - Page 13

• Manufacturer Part Number: DS32ELX0421SQX/NOPB
• Description: IC SERIALIZER 312.5GBPS 48LLP
• Manufacturer: National Semiconductor

Specifications of DS32ELX0421SQX/NOPB

• Function: Serializer
• Data Rate: 3.125Gbps
• Input Type: LVDS
• Output Type: CML
• Number Of Inputs: 5
• Number Of Outputs: 2
• Voltage - Supply: 2.5V, 3.3V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LLP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: DS32ELX0421SQX

SCRAMBLER and NRZI Encoder
The CDR of the DS32EL0124 and the DS32ELX0124 expect
a transition density of 20% for a period of 200 μs. If the scram-
bler and NRZI encoder are enabled, the raw or DC-balanced
serialized data is scrambled to improve transition density. The
scrambler accepts 20 bits of data and encodes it using the
polynomial X
to-NRZI converter before being output.
Enabling the scrambler can help to lower EMI emissions by
spreading the spectrum of the data. Scrambling also creates
transitions for the deserializer’s CDR to properly lock onto.
The scrambler and NRZI encoder are enabled or disabled by
default depending on how the DC_B and RS pins are config-
ured. To override the default scrambler setting two register
writes must be performed. First, write to register 22’h and set
bit 3 to unlock the scrambler register. Next write to register
21’h and change bit 4 to the desired value. The NRZI encoder
can be enabled or disabled independently of the scrambler by
controlling bit 7 of register 21'h and bit 4 of register 22'h.
CML OUTPUT DATA INTERFACING
The serial outputs provide low-skew differential signals. In-
ternal resistors connected from TxOUTn+ and TxOUTn- to
VDD25 terminate the outputs. The output level can be pro-
grammed by adjusting the pull-down resistor to the
VOD_CTRL pin. The output terminations can also be pro-
grammed to be either 50 Ω or 75 Ω.
The output buffer consists of a current mode logic (CML) driv-
er with user configurable de-emphasis control, which can be
used to optimize performance over a wide range of transmis-
sion line lengths and attenuation distortions resulting from low
cost CAT(-5, -6, -7) cable or FR–4 backplane. Output de-em-
9
+ X
4
+ 1. The data can then be sent to the NRZ-
FIGURE 7. Serializer State Diagram
13
phasis is user programmable through either device pins
DE_EMPH0 and DE_EMPH1 or SMBus interface. Users can
control the strength of the de-emphasis to optimize for a spe-
cific system environment. Please see the De-Emphasis Con-
trol Table for details.
De-Emphasis Control Table
The DS32ELX0421 provides a secondary serial output, sup-
porting redundancy applications. The redundant output driver
can be enabled by setting TXOUT1_EN pin to HIGH or by
activating it through the SMBus reigsters.
DEVICE CONFIGURATION
There are four ways to configure the DS32EL0421 and
DS32ELX0421 serializers, these combinations are shown in
Table
RS and DC_B pins change the link startup behavior of the
serializers. When connecting to a deserializer other than the
DS32EL0124 or DS32ELX0124, Remote Sense should be
disabled. The scrambler and NRZI encoder shown in
1
When Remote Sense is enabled, with RS pin tied low, the
serializer must be connected directly to a DS32EL0124 or
DS32ELX0124 deserializer without any active components
between them. The Remote Sense module features an up-
stream communication method for the serializer and deseri-
DE_EMPH[1:0]
00'b
01'b
10'b
11'b
can be enabled or disabled through register programming.
1. Refer to
Figure 7
30032115
Output De-Emphasis Level
Off
Low
Medium
High
to see how the combinations of the
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Table