8.4.8 Output Driver Settings for LVPECL, LVDS, HCSL, and CML
Each differential output has four settings for control:
• Normal or Low Power Format
• Amplitude (sometimes called Swing)
• Common Mode Voltage
• Stop High or Stop Low
The normal Format setting has a 100 Ω internal resistor between the plus and minus output pins. The Low Power Format setting
removes this 100 Ω internal resistor and then the differential output resistance will be > 500 Ω. However as long as the termination
impedance matches the differential impedance of the pcb traces the signal integrity across the termination impedance will be good.
For the same output amplitude the Low Power Format will use less power than the Normal Format. The Low Power Format also has
a lower rise/fall time than the Normal Format. See the Si5391/Si5391P data sheet for the rise/fall time specifications. For LVPECL and
LVDS standards, ClockBuilder Pro does not support the Low Power Differential Format. Stop High means that when the output driver is
disabled the plus output will be high and the minus output will be low. Stop Low means that when the output driver is disabled the plus
output will be low and the minus output will be high.
The Format, Amplitude and Common Mode settings for the various supported standards are shown in
Table 8.10. Settings for LVDS, LVPECL, and HCSL
OUTx_FORMAT
Standard
VDDO Volts
OUTx_CM
(Decimal)
OUTx_AMPL
(Decimal)
001 = Normal Differential
LVPECL
3.3
11
6
001 = Normal Differential
LVPECL
2.5
11
6
002 = Low Power Differential
LVPECL
3.3
11
3
002 = Low Power Differential
LVPECL
2.5
11
3
001 = Normal Differential
LVDS
3.3
3
3
001 = Normal Differential
LVDS
2.5
11
3
001 = Normal Differential
Sub-LVDS
1.8
13
3
002 = Low Power Differential
LVDS
3.3
3
1
002 = Low Power Differential
LVDS
2.5
11
1
002 = Low Power Differential
Sub-LVDS
1.8
13
1
002 = Low Power Differential
3.3
11
3
002 = Low Power Differential
2.5
11
3
002 = Low Power Differential
1.8
13
3
Note:
1. The low-power format will cause the rise/fall time to increase by approximately a factor of two. See the Si5391/Si5391P data
sheet for more information.
2. The common-mode voltage produced is not compliant with LVDS standards; therefore ac coupling the driver to an LVDS receiver
is highly recommended.
3. Creates HCSL compatible signal.
The output differential driver can produce a wide range of output amplitudes that includes CML amplitudes. See Section
the Differential Output Driver to Non-Standard Amplitudes
for additional information.
Si5391 Reference Manual • Outputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 0.5 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2022
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