ICS8430002 Datasheet, PDF (15/27 Pages) Integrated Device Technology – High-Performance Fractional-N Frequency Synthesizer

ICS8430002 Data Sheet
Application Information
Power Supply Filtering Technique
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 ICS8430002 provides
separate power supplies to isolate any high switching noise from the
outputs to the internal PLL. V_CC, V_CCA, and V_{CCO_X} should be
individually connected to the power supply plane through vias, and
0.01µF bypass capacitors should be used for each pin. Figure 2
illustrates this for a generic V_CC pin and also shows that V_CCA
requires that an additional 10Ω resistor along with a 10µF bypass
capacitor be connected to the V_CCA pin.
HIGH-PERFORMANCE FRACTIONAL-N FREQUENCY SYNTHESIZER
3.3V
V_CC
.01µF _10Ω
V_CCA
.01µF
10µF
Figure 2. Power Supply Filtering
Wiring the Differential Input to Accept Single-Ended Levels
Figure 3 shows how the differential input can be wired to accept
single ended levels. The reference voltage V_REF = V_CC/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 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_CC = 3.3V, V_REF should be 1.25V and R2/R1 =
0.609.
Single Ended Clock Input
VCC
R1
1K
PCLK
V_REF
C1
0.1u
nPCLK
R2
1K
Figure 3. Single-Ended Signal Driving Differential Input
ICS8430002AY REVISION C NOVEMBER 12, 2009
15
©2009 Integrated Device Technology, Inc.