IDT / ICS PCI EXPRESS JITTER ATTENUATOR
6
ICS9DB202CK-01 REV. B FEBRUARY 18, 2009
ICS9DB202-01
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
FIGURE 1. POWER SUPPLY FILTERING
24
Ω
V
DDA
10
μF
.01
μF
3.3V
.01
μF
V
DD
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter perfor-
mance, power supply isolation is required. The ICS9DB202-01
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD and VDDA should be
individually connected to the power supply plane through vias,
and 0.01F bypass capacitors should be used for each pin.
Fig-
ure 1 illustrates this for a generic V
DD pin and also shows that
V
DDA requires that an additional 24Ω resistor along with a 10F
bypass capacitor be connected to the V
DDA pin.