© 2014 Exar Corporation

XR81111

Universal Clock - High Frequency

LVPECL Clock Synthesizer

exar.com/XR81111

Rev 1B

1 / 12

General Description

The XR81111-CA04 is a clock synthesizer with Integer divider, LVPECL

driver, 3.3V/2.5V supply, taking a 25MHz Xtal input and providing one of four

selectable output frequencies. The device is optimized for use with a 25MHz

crystal (or system clock) and generates a selection of output frequencies -

156.25MHz for 10GE/XAUI, 150MHz for SAS, 125MHz for GE and 100MHz

for PCIe applications.

The application diagram below shows a typical synthesizer configuration

with any standard crystal oscillating in fundamental mode. Internal load

capacitors are optionally available to minimize/eliminate external crystal

loads. A system clock can also be used to overdrive the oscillator for a syn-

chronous timing system.

The typical phase noise plot below shows the jitter integrated over the

12KHz to 20MHz range that is widely used in WAN systems. Most LAN

applications however use the integration range of 1.875MHz to 20MHz.

These clock devices show a very good high frequency noise floor below -

150dB.

The XR81111 is a family of Universal Clock synthesizer devices in QFN-10

packages that are footprint compatible with industry standard 5mm x 7mm

oscillators. The devices generate ANY frequency in the range of 100 MHz to

1.5GHz by utilizing a highly flexible delta sigma modulator and a wide rang-

ing VCO. The high clock frequency LVPECL outputs have very low phase

noise jitter of sub 0.6ps, while consuming extremely low power. These

devices can be used with standard crystals or external system clock and can

be configured to select from four different frequency multiplier settings to

support a wide variety of applications. This family of products have an

extremely low power PLL block with core power consumption less than 40%

of the equivalent devices from competition. By second sourcing several of

the existing sockets, these devices provides a very compelling power effi-

ciency value benefit across all market segments.

Other clock multiplier and/or driver configurations are possible in this clock

family and can be requested from the factory

FEATURES

• XR81111-CA04: Factory Configured

• Footprint compatible with 5mm x 7mm differen-

tial oscillators

• One differential LVPECL output pair

• Crystal oscillator interface which can also be

overdriven using a single-ended reference clock

• Output frequency range: 100MHz - 156.25MHz

• Crystal/input frequency: 25MHz, parallel resonant

crystal

• VCO range: 2GHz - 3GHz

• RMS phase jitter @ 156.25MHz, 12kHz - 20MHz:

<0.60ps

• Full 3.3V or 2.5V operating supply

• -40°C to 85°C ambient operating temperature

• Lead-free (RoHS 6) package

APPLICATIONS

• 10GE, GE LAN/WAN

• 2.5G/10G SONET/SDH/OTN

• xDSL, PCIe

• Low-jitter Clock Generation

• Synchronized clock systems

Typical Application

2.5V or 3.3V

Q

100 MHz to 156.25MHz

Q

OE

XTAL_IN

XTAL_OUT

FSEL1

FSEL0

25MHz

Enable

Freq Select

XR81111 CA04

XR81111 PHASE NOISE (dBc/Hz)

100Hz

1KHz

10KHz

100 KHz

1MHz

10MHz

-120db

-160db

-140db

-100db

-80db

-60db

-180db

-40db

RMS Jitter = 532.3fs

Int Range 12KHz to 20MHz