SI5335 Datasheet, PDF (29/47 Pages) Silicon Laboratories – WEB-CUSTOMIZABLE, ANY-FREQUENCY, ANY-OUTPUT QUAD CLOCK GENERATOR/BUFFER

Si5335
3.10.3.2. AC Coupled LVPECL Outputs
AC coupling is necessary when a receiver and a driver have compatible voltage swings but different common-
mode voltages. AC coupling works well for dc-balanced signals, such as for 50% duty cycle clocks. Figure 18
describes two methods for ac coupling the standard LVPECL driver. The Thevenin termination shown in Figure 18a
is a convenient and common approach when a V_BB (V_DD – 1.3 V) supply is not available; however, it does
consume additional power. The termination method shown in Figure 18b consumes less power. A V_BB supply can
be generated from a simple voltage divider circuit as shown in Figure 18b.
3.3 V, 2.5 V
Si5335
V_DDOx
0.1 µF
CLKxA
50
LVPECL
CLKxB
50
Rb Rb
0.1 µF
V_DDO V_DDO
R₁
R₁
Keep termination close to
the receiver
3.3 V LVPECL
2.5 V LVPECL
R₂
R₂
V_DDO – 1.3 V
R₁ // R₂ = 50 
3.3 V LVPECL
R₁ = 82.5 
R₂ = 127 
Rb = 130  (2.5 V LVPECL)
Rb = 200 
(3.3 V LVPECL)
a. AC-Coupled with Thevenin Termination
2.5 V LVPECL
R₁ = 62.5 
R₂ = 250 
Si5335
3.3 V, 2.5 V
V_DDOx
LVPECL
CLKxA
CLKxB
Rb = 130  (2.5 V LVPECL)
Rb = 200  (3.3 V LVPECL)
Rb Rb
Keep termination close to
the receiver
0.1 µF
50
0.1 µF
50
V_BB
50
50
V_DDO – 1.3 V
3.3 V LVPECL
2.5 V LVPECL
V_DDO
R₁
V_BB
0.1 µF
R₂
b. AC Coupled with 100  Termination
Figure 18. Interfacing to an LVPECL Receiver Using AC Coupling
Rev. 1.4
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