13. Appendix—Custom Differential Amplitude Controls
In some customer applications, it may be desirable to have larger or smaller differential amplitudes than those produced by the stand-
ard LVPECL and LVDS settings generated by ClockBuilder Pro. For example, "CML" format is sometimes desired for an application,
but CML is not a defined standard, and, hence, the input amplitude of CML signals may differ between receivers. In these cases, the
following information describes how to implement non-standard differential amplitudes. All output driver settings in this Appendix must
have the differential driver ac-coupled or else the signal integrity may be severely compromised.
The differential output driver has two basic modes of operation as well as variable output amplitude capability. The Normal mode has
an internal impedance of 100 Ω differential, while the Low Power mode has an internal impedance of >500 Ω differential. In both cases,
when properly terminated with 100 Ω differential externally, the typical amplitudes listed in the table below result. Each differential output
driver can be configured for the amplitudes listed in the table below using the Format selection field on the CBPro Define Output Clocks
page.
Table 13.1. Differential Output Amplitude Typical Values
OUTx_AMPL
Normal Mode
OUTx_FORMAT = 1
(mVpp-SE)
Low-Power Mode
OUTx_FORMAT = 2
(mVpp-SE)
0
130
200
1
230
400
2
350
620
3
450
820
4
575
1010
5
700
1200
6
810
1350
1
7
920
1600
1
Note:
1. In Low-Power mode with VDDO=1.8 V, OUTx_AMPL may not be set to 6 or 7.
2. These amplitudes are based upon 100 Ω differential termination.
For applications using a custom differential output amplitude, the common mode voltage should be selected as shown in the table
below. These selections, along with the settings given in
4.5.4 Recommended Settings for Differential LVPECL, LVDS, HCSL, and
, have been verified to produce good signal integrity. No other combinations of amplitude and common mode settings are allowed
unless they are set by CBPro to implement LVPECL, LVDS, HCSL or High Speed Differential configurations as signal integrity may be
compromised.
Also, in cases where the receiver is dc-biased, either internally or through an external network, the outputs of the device must be
ac-coupled. Output driver performance is not guaranteed when dc-coupled to a biased-input receiver.
Table 13.2. Differential Output Common Mode Voltage Selections
VDDO (Volts)
Differential Format
OUTx_FORMAT
Common Mode Voltage
(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
Si5386 Rev. E Reference Manual • Appendix—Custom Differential Amplitude Controls
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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