780MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER
84320-01 DATA SHEET
10 REVISION D 5/26/16
CRYSTAL INPUT INTERFACE
A crystal can be characterized for either series or parallel mode
operation. The 84320-01 has a built-in crystal oscillator circuit.
This interface can accept either a series or parallel crystal
without additional components and generate frequencies with
FIGURE 3. CRYSTAL INPUt INTERFACE
accuracy suitable for most applications. Additional accuracy
can be achieved by adding two small capacitors C1 and C2 as
shown in Figure 3.
LVCMOS TO XTAL INTERFACE
The XTAL_IN input can accept a single-ended LVCMOS signal
through an AC coupling capacitor. A general interface diagram is
shown in Figure 4. The XTAL_OUT pin can be left fl oating. The
input edge rate can be as slow as 10ns. For LVCMOS inputs,
it is recommended that the amplitude be reduced from full
swing to half swing in order to prevent signal interference with
the power rail and to reduce noise. This confi guration requires
FIGURE 4. GENERAL DIAGRAM FOR LVCMOS DRIVER TO XTAL INPUT INTERFACE
that the output impedance of the driver (Ro) plus the series
resistance (Rs) equals the transmission line impedance. In
addition, matched termination at the crystal input will attenuate
the signal in half. This can be done in one of two ways. First, R1
and R2 in parallel should equal the transmission line impedance.
For most 50Ω applications, R1 and R2 can be 100Ω. This can
also be accomplished by removing R1 and making R2 50Ω.
