8.4.3 Programmable Common Mode Voltage for Differential Outputs
The common mode voltage (VCM) for the differential Normal and High Swing modes is programmable in 100 mV increments from 0.7
to 2.3 V depending on the voltage available at the output's VDDO pin. Setting the common mode voltage is useful when dc coupling the
output drivers. High swing mode may also cause an increase in the rise/fall time.
Table 8.5. Differential Output Common Mode Voltage Control Registers
Setting Name
Hex Address [Bit
Field]
Function
Si5391/Si5391P
OUT0A_CM
0105[3:0]
Sets the common mode voltage for the differential output driver.
See
Table 8.10 Settings for LVDS, LVPECL, and HCSL on page
OUT0_CM
010A[3:0]
OUT1_CM
010F[3:0]
OUT2_CM
0114[3:0]
OUT3_CM
0119[3:0]
OUT4_CM
011E[3:0]
OUT5_CM
0123[3:0]
OUT6_CM
0128[3:0]
OUT7_CM
012D[3:0]
OUT8_CM
0132[3:0]
OUT9_CM
0137[3:0]
OUT9A_CM
013C[3:0]
8.4.4 LVCMOS Output Terminations
LVCMOS outputs are dc-coupled as shown in
Figure 8.4 LVCMOS Output Terminations on page 31
.
3.3V, 2.5V, 1.8V
LVCMOS
V
DDO
= 3.3V, 2.5V, 1.8V
50
Rs
50
Rs
DC Coupled LVCMOS
OUTx
OUTx
Figure 8.4. LVCMOS Output Terminations
8.4.5 LVCMOS Output Impedance and Drive Strength Selection
Each LVCMOS driver has a configurable output impedance to accommodate different trace impedances and drive strengths. A
source termination resistor is recommended to help match the selected output impedance to the trace impedance. There are three
programmable output impedance selections for each VDDO option as shown below. The value for the OUTx_CMOS_DRIVE bits are
given.
Si5391 Reference Manual • Outputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
31
Rev. 0.5 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • January 11, 2022
31