ICS843002I-41

700MHZ, FEMTOCLOCKS™ VCXO BASED SONET/SDH JITTER ATTENUATOR

IDT™ / ICS™ VCXO BASED SONET/SDH JITTER ATTENUATOR

17

ICS843002AKI-41 REV. A OCTOBER 25, 2007

Choosing the correct external components and having a proper

printed circuit board (PCB) layout is a key task for quality operation

of the VCXO-PLL. In choosing a crystal, special precaution must

frequency, accuracy and temperature range must also be

considered. Since the pulling range of a crystal also varies with

the package, it is recommended that a metal-canned package like

HC49 be used. Generally, a metal-canned package has a larger

pulling range than a surface mounted device (SMD). For crystal

selection information, refer to the VCXO Crystal Selection

Application Note.

resonating frequency and is closely related to the VCXO tuning

range. The total external capacitance seen by the crystal when

installed on a board is the sum of the stray board capacitance, IC

package lead capacitance, internal varactor capacitance and any

VCXO will oscillate at a higher frequency than the crystal

capacitance, the VCXO will oscillate at a lower frequency than the

crystal specification. In either case, the absolute tuning range is

Parameter Table balances the tuning range by centering the

tuning curve.

configurations. The device has been characterized using these

parameters. For other configurations, refer to the Loop Filter

Component Selection for VCXO Based PLLs Application Note.

The crystal and external loop

filter components should be

kept as close as possible to the

device. Loop filter and crystal

traces should be kept short and

separated from each other.

Other signal traces should be

kept separate and not run

underneath the device, loop

filter or crystal components.

VCXO Characteristics Table

VCXO-PLL Loop Bandwidth Selection Table

Crystal Characteristics

LF0

LF1

ISET

XTAL_IN

XTAL_OUT

C

S

C

P

R

SET

C

TUNE

C

TUNE

19.44MHz

Symbol

Parameter

Typical

Units

VCXO Gain

5800

Hz/V

Low Varactor Capacitance

12.6

pF

High Varactor Capacitance

24.5

pF

Bandwidth

Crystal Frequency (MHz)

10Hz (Low)

19.44

5

1.0

0.10

9.5

70Hz (Mid)

19.44

10

1.0

0.01

4.75

100Hz (High)

19.44

15

1.0

0.01

4.75

Symbol

Parameter

Test Conditions

Minimum

Typical

Maximum

Units

Mode of Oscillation

Fundamental

Frequency

19.44

MHz

Frequency Tolerance

±20

ppm

Frequency Stability

±20

ppm

Operating Temperature Range

-40

+85

Load Capacitance

12

pF

Shunt Capacitance

4

pF

Pullability Ratio

220

240

ESR

Equivalent Series Resistance

50

Ω

Drive Level

1mW

±3 per year

ppm