ICS813001I Datasheet, PDF (9/18 Pages) Integrated Circuit Systems – DUAL VCXO W/3.3V, 2.5V LVPECL FEMTOCLOCK-TM PLL

Integrated
Circuit
Systems, Inc.
ICS813001I
DUAL VCXO W/3.3V, 2.5V LVPECL
FEMTOCLOCK™ PLL
VCXO CRYSTAL SELECTION
Choosing a crystal with the correct characteristics is one of
the most critical steps in using a Voltage Controlled Crystal
Oscillator (VCXO). The crystal parameters affect the tuning
range and accuracy of a VCXO. Below are the key variables
and an example of using the crystal parameters to calculate
the tuning range of the VCXO.
➤ ^VC
Control Voltage
C_V
➤
C
S1
Oscillator
VCXO (Internal)
XTAL
V_C
- Control voltage used to tune
frequency
C_V
- Varactor capacitance, varies due to
➤_CV
the
change in control voltage
C C - Load tuning capacitance used for fine
L1, L2
tuning or centering nominal
frequency
C_S1, C_{S2 - Stray Capacitance caused by pads,}
C
S2
vias, and other board parasitics
C_L1
C_L2
➤
Optional
FIGURE 3. VCXO OSCILLATOR CIRCUIT
TABLE 6. EXAMPLE CRYSTAL PARAMETERS
Symbol Parameter
f_N
Nominal Frequency
f_T
Frequency Tolerance
f
Frequency Stability
S
Operating Temperature Range
C_L
C_O
C_1, C₂
ESR
Load Capacitance
Shunt Capacitance
Pullability Ratio
Equivalent Series Resistance
Drive Level
Aging @ 25°C
Mode of Operation
Test Conditions
Minimum Typical Maximum
14
24
±20
±20
0
70
12
4
220
240
20
1
±3 per year
Fundamental
Units
MHz
ppm
ppm
°C
pF
pF
mW
ppm
813001AGI
www.icst.com/products/hiperclocks.html
9
REV. A SEPTEMBER 2, 2005