LMK03200EVAL National Semiconductor, LMK03200EVAL Datasheet - Page 35

• Manufacturer Part Number: LMK03200EVAL
• Description: BOARD EVALUATION LMK03200
• Manufacturer: National Semiconductor

Specifications of LMK03200EVAL

• Main Purpose: Timing, Clock Conditioner
• Embedded: No
• Utilized Ic / Part: LMK03200
• Primary Attributes: 3 LVDS & 5 LVPECL Outputs, Integrated PLL & VCO
• Secondary Attributes: 3.15 V ~ 3.45 V Supply
• Silicon Manufacturer: National
• Silicon Core Number: LMK03200
• Kit Application Type: Clock & Timing
• Application Sub Type: Precision Clock Conditioner
• Kit Contents: Board, Cable
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FIGURE 10. Differential LVPECL Operation, DC Coupling,
FIGURE 9. 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. One way to do this is with the termination circuitry in
Figure
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 12. Differential LVPECL Operation, AC Coupling,
FIGURE 11. Differential LVDS Operation, AC Coupling
Figure
11.
10.
12. For proper receiver operation, the signal should
Thevenin Equivalent
Figure 12
for Vcc = 3.3 V. Note this
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