AD9516-5PCBZ datasheet(73/76 Pages) AD

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AD9516-5

Rev. A | Page 73 of 76

CMOS

10Ω

60.4Ω

(1.0 INCH)

MICROSTRIP

CMOS CLOCK DISTRIBUTION

The AD9516 provides four clock outputs (OUT6 to OUT9)

that are selectable as either CMOS or LVDS level outputs. When

selected as CMOS, each output becomes a pair of CMOS outputs,

each of which can be individually turned on or off and set as

noninverting or inverting. These outputs are 3.3 V CMOS

compatible.

Figure 63. Series Termination of CMOS Output

Termination at the far end of the PCB trace is a second option.

The CMOS outputs of the AD9516 do not supply enough current

to provide a full voltage swing with a low impedance resistive, far-

end termination, as shown in Figure 64. The far-end termination

network should match the PCB trace impedance and provide the

desired switching point. The reduced signal swing may still meet

receiver input requirements in some applications. This can be

useful when driving long trace lengths on less critical nets.

Whenever single-ended CMOS clocking is used, some general

guidelines should be followed.

Point-to-point nets should be designed such that a driver has

only one receiver on the net, if possible. This allows for simple

termination schemes and minimizes ringing due to possible

mismatched impedances on the net. Series termination at the

source is generally required to provide transmission line matching

and/or to reduce current transients at the driver. The value of

the resistor is dependent on the board design and timing

requirements (typically 10 Ω to 100 Ω is used). CMOS outputs

are also limited in terms of the capacitive load or trace length

that they can drive. Typically, trace lengths less than 3 inches

are recommended to preserve signal rise/fall times and preserve

signal integrity.

CMOS

10Ω

50Ω

100Ω

Figure 64. CMOS Output with Far-End Termination

Because of the limitations of single-ended CMOS clocking,

consider using differential outputs when driving high speed

signals over long traces. The AD9516 offers both LVPECL and

LVDS outputs that are better suited for driving long traces where

the inherent noise immunity of differential signaling provides

superior performance for clocking converters.

AD9516-5PCBZ Datasheet(PDF) 73 Page - Analog Devices

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