REVISION A 4/20/15
841654 DATA SHEET
9 FEMTOCLOCKS™ CRYSTAL-TO-HCSL
CLOCK GENERATOR
PARAMETER MEASUREMENT INFORMATION, CONTINUED
SE MEASUREMENT POINTS FOR ABSOLUTE CROSS POINT/SWING
APPLICATION INFORMATION
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. To achieve optimum jitter
performance, power supply isolation is required. The 841654
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD,
V
DDA,
V
DDOA
and
V
DDOB
should be individually connected to the power supply
plane through vias, and 0.01µF bypass capacitors should be
used for each pin. Figure 1 illustrates this for a generic V
DD
pin and also shows that V
DDA
requires that an additional10Ω
resistor along with a 10µF bypass capacitor be connected to the
V
DDA
pin.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
10Ω
V
DDA
10μF
.01μF
3.3V
.01μF
V
DD
INPUTS:
CRYSTAL INPUTS
For applications not requiring the use of the crystal oscillator input,
both XTAL_IN and XTAL_OUT can be left fl oating. Though not
required, but for additional protection, a 1kΩ resistor can be tied
from XTAL_IN to ground.
REF_IN I
NPUT
For applications not requiring the use of the reference clock,
it can be left fl oating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the REF_IN to ground.
LVCMOS C
ONTROL PINS
All control pins have internal pull-ups or pull-downs; additional
resistance is not required but can be added for additional protection.
A 1kΩ resistor can be used.
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
OUTPUTS:
HCSL OUTPUTS
All unused HCSL outputs can be left fl oating. We recommend that
there is no trace attached. Both sides of the differential output pair
should either be left fl oating or terminated.
LVCMOS O
UTPUT
The unused LVCMOS output can be left fl oating. We recommend
that there is no trace attached.
