84427 Datasheet, PDF (7/16 Pages) Integrated Device Technology – Crystal-to-LVDS Integrated Frequency Synthesizer/Fanout Buffer

84427 DATA SHEET
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply
pins are vulnerable to random noise. The 84427 provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL.V_DD and V_DDA should be
individually connected to the power supply plane through vias,
and bypass capacitors should be used for each pin. To achieve
optimum jitter performance, power supply isolation is required.
Figure 1 illustrates how a 24Ω resistor along with a 10μF and a
.01μF bypass capacitor should be connected to each V_DDA pin.
V_DD
V_DDA
3.3V
.01μF 24Ω
.01μF
10 μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The 84427 has been characterized with 18pF parallel resonant
crystals. The capacitor values, C1 and C2, shown in Figure 2
below were determined using an 18pF parallel resonant crystal
and were chosen to minimize the ppm error. The optimum C1
and C2 values can be slightly adjusted for different board layouts.
REVISION B 5/6/15
X1
18pF Parallel Crystal
XTAL_IN
C1
18p
XTAL_OUT
C2
22p
Figure 2. CRYSTAL INPUt INTERFACE
7
CRYSTAL-TO-LVDS
INTEGRATED FREQUENCY SYNTHESIZER/FANOUT BUFFER