3.2 Types of Inputs
Each of the four different inputs IN0-IN3 can be configured as ac-coupled differential formats such as LVDS, LVPECL, HCSL, CML, and
ac-coupled single-ended CMOS formats. The standard format inputs have a nominal 50% duty cycle, must be ac-coupled and use the
“Standard” input buffer selection as these pins are internally dc-biased to approximately 0.83 V.
Floating clock inputs are noise sensitive. Add a cap to ground for all non-CMOS unused clock inputs. To place the input into Standard
Mode make sure IN_PULSED_CMOS_EN 0x949 [7:4] = 0. Bit 7 = IN3, Bit 6 = IN2, Bit 5 = IN1 and Bit 4 = IN0. Make sure the corre-
sponding input bit is set to 0 for Standard Mode. If this bit is 1 this will turn on dc-coupled CMOS Mode. Setting IN_PULSED_CMO_EN
enables all dc-coupled CMOS modes described below.
50
100
INx
INxb
50
Standard AC-Coupled Differential
LVDS, LVPECL, CML
Standard AC-Coupled Single-Ended
INx
3.3 V, 2.5 V, 1.8 V
LVCMOS
R1
R
2
50
RS
RS matches the CMOS driver to a
50 ohm transmission line (if used)
C1
INxb
*This cap should have less than ~20 ohms of capacitive reactance at the clock input
frequency.
** Only when 3.3 V LVCMOS driver is present, use R2 = 845 ohm and R1 = 267 ohm if
needed to keep the signal at INx < 3.6 Vpp_se. Including C1 = 6 pf may improve the
output jitter due to faster input slew rate at INx. If attenuation is not needed for
Inx<3.6Vppse, make R1 = 0 ohm and omit C1, R2 and the capacitor below R2. C1, R1,
and R2 should be physically placed as close as practical to the device input pins.
0.1uF
*
0.1uF
*
* These caps should have < ~5 ohms capacitive reactance at the clock input frequency.
0.1uF
*
0.1uF
0.1uF
Clock IC
Standard
Clock IC
Standard
**
Figure 3.1. AC-Coupled Standard Input Termination Diagrams
Si5386 Rev. E Reference Manual • Clock Inputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
19
Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
19