15. Appendix—Setting the Differential Output Driver to Non-Standard Amplitudes
In some applications it may be desirable to have larger or smaller differential amplitudes than produced by the standard LVPECL and
LVDS settings, as selected by CBPro. In these cases, the following information describes how to implement these amplitudes by writing
to the OUTx_CM and OUTx_AMPL setting names. Contact Silicon Labs for assistance if you want your custom configured device to be
programmed for any of the settings in this appendix.
The differential output driver has a variable output amplitude capability and 2 basic formats, normal and low power format. The
difference between these two formats is that the normal format has an output impedance of ~100 ohms differential and the low power
format has an output impedance of > 500 Ω differential. Note that the rise/fall time is slower when using the Low Power Differential
Format. See the Si5341/40 data sheet for the rise/fall time specifications.
If the standard LVDS or LVPECL compatible output amplitudes will not work for a particular application, the variable amplitude capability
can be used to achieve higher or lower amplitudes. For example, a “CML” format is sometimes desired for an application. However,
CML is not a defined standard and hence the amplitude of a CML signal for one receiver may be different than that of another receiver.
When the output amplitude needs to be different than standard LVDS or LVPECL, the Common Mode Voltage settings must be
set as shown in the table below. No settings other than the ones in the table below are supported as the signal integrity could be
compromised. In addition the output driver should be ac-coupled to the load so that the common mode voltage of the driver is not
affected by the load.
Table 15.1. Output Differential Common-Mode Voltage Settings
VDDOx(Volts)
Differential Format
OUTx_FORMAT
Common Mode Volt-
age(Volts)
OUTx_CM
3.3
Normal
0x1
2.0
0xB
3.3
Low Power
0x2
1.6
0x7
2.5
Normal
0x1
1.3
0xC
2.5
Low Power
0x2
1.1
0xA
1.8
Normal
0x1
0.8
0xD
1.8
Low Power
0x2
0.8
0xD
The differential amplitude can be set as shown in the following table:
OUTx_AMPL
Normal Differential Format(Vpp SE mV–Typi-
cal)
Low Power Differential
Format(Vpp SE mV – Typical)
0
130
200
1
230
400
2
350
620
3
450
820
4
575
1010
5
700
1200
6
810
13501
7
920
16001
See the register map portion of this document for additional information about OUTx_FORMAT, OUTx_CM and OUTx_AMPL. Contact
for assistance at if you require a factory-programmed device to be configured for any of the output driver settings in this
appendix.
Si5341, Si5340 Rev D Family Reference Manual • Appendix—Setting the Differential Output Driver to Non-Standard Amplitudes
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.3 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • July 26, 2021
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