LMK03033CISQE National Semiconductor, LMK03033CISQE Datasheet - Page 25

• Manufacturer Part Number: LMK03033CISQE
• Manufacturer: National Semiconductor

Specifications of LMK03033CISQE

• Lead Free Status / Rohs Status: Not Compliant

FIGURE 8. Differential LVPECL Operation, DC Coupling,
FIGURE 7. Differential LVPECL Operation, DC Coupling
Thevenin Equivalent
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3.7.2 Termination for AC Coupled Differential Operation
AC coupling allows for shifting the DC bias level (common
mode voltage) when driving different receiver standards.
Since AC coupling prevents the driver from providing a DC
bias voltage at the receiver it is important to ensure the re-
ceiver is biased to its ideal DC level.
When driving LVDS receivers with an LVDS driver, the signal
may be AC coupled by adding DC blocking capacitors, how-
ever the proper DC bias point needs to be established at the
receiver. If the receiver does not automatically bias its input,
one way to do this is with the termination circuitry in
9.
When using AC coupling with LVDS outputs, there may be a
startup delay observed in the clock output due to capacitor
charging.
need to be adjusted to meet the startup requirements for a
particular application.
LVPECL drivers require a DC path to ground. When AC cou-
pling an LVPECL signal use 120 Ω emitter resistors close to
the LVPECL driver to provide a DC path to ground as shown
in
be biased to the DC bias level (common mode voltage) spec-
ified by the receiver. The typical DC bias voltage (common
mode voltage) for LVPECL receivers is 2 V. A Thevenin
equivalent circuit (82 Ω resistor connected to Vcc and a 120
Ω resistor connected to ground with the driver connected to
the junction of the 82 Ω and 120 Ω resistors) is a valid termi-
nation as shown in
Thevenin circuit is different from the DC coupled example in
Figure
FIGURE 10. Differential LVPECL Operation, AC Coupling,
FIGURE 9. Differential LVDS Operation, AC Coupling
Figure
8.
10. For proper receiver operation, the signal should
Figure 9
employs 0.1 µF capacitors. This value may
Thevenin Equivalent
Figure 10
for Vcc = 3.3 V. Note this
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Figure