AD9510 Analog Devices, AD9510 Datasheet - Page 39

• Manufacturer Part Number: AD9510
• Manufacturer: Analog Devices

Preliminary Technical Data
Termination at the far end of the PCB trace is a second option.
The CMOS outputs of the AD9510 do not supply enough
current to provide a full voltage swing with a low impedance
resistive, far-end termination, as shown in Figure 28. 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.
CMOS
OUT4, OUT5, OUT6, OUT7
selected as CMOS
Figure 28. Far-End Termination of CMOS Output Waveform
Figure 27. CMOS Output with Far-End Termination
10Ω
Figure 26. CMOS Output Waveforms
50Ω
100Ω
100Ω
Vpullup=3.3V
3pF
Rev. PrA | Page 39 of 41
Because of the limitations of single-ended CMOS clocking,
consider using differential outputs when driving high speed
signals over long traces. The AD9510 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.
LVPECL CLOCK DISTRIBUTION
The low voltage positive emitter coupled logic (LVPECL)
outputs of the AD9510 provide the lowest jitter clock signals
available from the AD9510. The LVPECL outputs (because they
are open emitter) require a dc termination to bias the output
transistors. A simplified equivalent circuit in Figure 29 shows
the LVPECL output stage.
In most applications, a standard LVPECL far-end termination is
recommended, as shown in Figure 30. The resistor network is
designed to match the transmission line impedance (50 Ω) and
the desired switching threshold (1.3 V). Figure 32 shows a
typical LVPECL clock waveform.
3.3V
LVPECL
LVPECL
Figure 29. Simplified LVPECL Output Stage
50Ω
50Ω
Figure 30. LVPECL Far-End Termination
single-ended (not c oupled)
Vt=Vcc - 1.3V
GND
3.3V
127Ω
83Ω
Out-
Out+
3.3V
127Ω
83Ω
AD9510
3.3V
LVPECL
LVPECL