DS92LV2421_16 Datasheet, PDF (25/59 Pages) Texas Instruments – 10-MHz to 75-MHz, 24-Bit Channel Link II Serializer And Deserializer

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DS92LV2421, DS92LV2422
SNLS321C – MAY 2010 – REVISED MAY 2016
Feature Description (continued)
7.3.3.1.2 Serializer Spread Spectrum Compatibility
The serializer CLKIN is capable of tracking spread spectrum clocking (SSC) from a host source. The CLKIN
accepts spread spectrum tracking up to 35-kHz modulation and ±0.5, ±1, or ±2% deviations (center spread). The
maximum conditions for the CLKIN input are: a modulation frequency of 35 kHz and amplitude deviations of ±2%
(4% total).
7.3.3.2 Signal Quality Enhancers
7.3.3.2.1 Serializer VOD Select (VODSEL)
The serializer differential output voltage may be increased by setting the VODSEL pin high. When VODSEL is
low, the DC VOD is at the standard (default) level. When VODSEL is high, the VOD is increased in level. The
increased VOD is useful in extremely high noise environments and also on extra long cable length applications.
When using de-emphasis, TI recommends setting VODSEL = H to avoid excessive signal attenuation, especially
with the larger de-emphasis settings. This feature may be controlled by the external pin or by register.
Table 2. Differential Output Voltage
INPUT
VODSEL
H
L
VOD (mV)
±420
±280
EFFECT
VOD (mV_p-p)
840
560
7.3.3.2.2 Serializer De-Emphasis (De-Emph)
The de-emphasis pin controls the amount of de-emphasis beginning one full bit time after a logic transition that
the serializer drives. This is useful to counteract loading effects of long or lossy cables. This pin must be left
open for standard switching currents (no de-emphasis) or if controlled by register. De-emphasis is selected by
connecting a resistor on this pin to ground, with R value between 0.5 kΩ to 1 MΩ, or by register setting. When
using de-emphasis, TI recommends to set VODSEL = H.
Table 3. De-Emphasis Resistor Value
RESISTOR VALUE (kΩ)
Open
0.6
1
2
5
DE-EMPHASIS SETTING
Disabled
–12 dB
–9 dB
–6 dB
–3 dB
0.00
-2.00
VDD = 1.8V,
T_A = 25^oC
-4.00
-6.00
-8.00
-10.00
-12.00
-14.00
1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06
R VALUE - LOG SCALE (:)
Figure 25. De-Emphasis vs R Value
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