ICS9DB202_06 Datasheet, PDF (7/13 Pages) Integrated Device Technology – PCI EXPRESS JITTER ATTENUATOR

ICS9DB202
PCI EXPRESS JITTER ATTENUATOR
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. The ICS9DB202 provides separate
power supplies to isolate any high switching noise from the out-
puts to the internal PLL. V_DD and V_DDA should be individually con-
nected to the power supply plane through vias, and bypass ca-
pacitors should be used for each pin. To achieve optimum jitter
performance, power supply isolation is required. Figure 1 illus-
trates how a 24Ω resistor along with a 10µF and a .01µF bypass
capacitor
should
be
connected
to
each
V
DDA
pin.
The
10Ω
resis-
tor can also be replaced by a ferrite bead.
3.3V
V
DD
.01µF 24Ω
V_DDA
.01µF
10µF
FIGURE 1. POWER SUPPLY FILTERING
WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS
Figure 2 shows how the differential input can be wired to accept
single ended levels. The reference voltage V_REF = V /2 is
DD
generated by the bias resistors R1, R2 and C1. This bias circuit
should be located as close as possible to the input pin. The ratio
of R1 and R2 might need to be adjusted to position the V_REF in
the center of the input voltage swing. For example, if the input
clock swing is only 2.5V and V = 3.3V, V_REF should be 1.25V
DD
and R2/R1 = 0.609.
VDD
Single Ended Clock Input
V_REF
C1
0.1u
R1
1K
CLK
nCLK
R2
1K
FIGURE 2. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
IDT^™ / ICS^™ PCI EXPRESS JITTER ATTENUATOR
7
ICS9DB202CG REV B JULY 14, 2006