IDT / ICS PCI EXPRESS JITTER ATTENUATOR
7
ICS9DB202CG REV B JULY 14, 2006
ICS9DB202
PCI EXPRESS JITTER ATTENUATOR
APPLICATION INFORMATION
Figure 2 shows how the differential input can be wired to accept
single ended levels. The reference voltage V_REF = V
DD
/2 is
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
FIGURE 2. SINGLE ENDED SIGNAL DRIVING DIFFERENTIAL INPUT
WIRING THE DIFFERENTIAL INPUT TO ACCEPT SINGLE ENDED LEVELS
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
DD
= 3.3V, V_REF should be 1.25V
and R2/R1 = 0.609.
V_REF
R1
1K
C1
0.1u
R2
1K
Single Ended Clock Input
CLK
nCLK
VDD
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 VDDA 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 24
resistor along with a 10F and a .01F bypass
capacitor should be connected to each V
DDA pin. The 10 resis-
tor can also be replaced by a ferrite bead.
FIGURE 1. POWER SUPPLY FILTERING
24
V
DDA
10
F
.01
F
3.3V
.01
F
V
DD