© 2014 Exar Corporation

XR81112

Universal Clock - High Frequency

LVCMOS/LVDS/LVPECL Clock Synthesizer

exar.com/XR81112

Rev 1A

1 / 12

General Description

The XR81112 is a family of Universal Clock synthesizer devices in a com-

pact QFN-12 package. The devices generate ANY frequency in the range of

10 MHz to 1.5GHz by utilizing a highly flexible delta sigma modulator and a

wide ranging VCO. The outputs are configurable for single ended LVCMOS

or differential LVDS or LVPECL. The clock 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 an 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 equivalent devices in the market.

The XR81112 is a clock synthesizer with Integer/fractional divider, LVCMOS/

LVDS/LVPECL driver, 3.3V/2.5V supply, taking a Xtal input and providing

one of four selectable output frequencies. The device is optimized for use

with a fundamental mode 10MHz to 60MHz crystal (or system clock) and

generates a selection of output frequencies from 10MHz to 1.5GHz in either

integer or fractional mode. In fractional mode, frequency resolution of less

than 1Hz steps can be achieved.

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. The typical

noise for the integration range of 1.875MHz to 20MHz is sub 200fs which is

important for LAN applications. These clock devices show a very good high

frequency noise floor below -150dB.

FEATURES

• Small footprint 3mm x 3mm QFN package

• Configurable - As one differential LVPECL/LVDS

output pair or as a single ended LVCMOS output

• Crystal oscillator interface which can also be

overdriven using a single-ended reference clock

• Output frequency range: 10MHz - 1500MHz

• Crystal/input frequency: 10MHz to 60MHz, paral-

lel 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

XR81112 PHASE NOISE (dBc/Hz) @ 156.25MHz

100Hz

1KHz

10KHz

100KHz

1MHz

10MHz

-120db

-160db

-140db

-100db

-80db

-60db

-180db

-40db

RMS Jitter = 542.0fs

Int Range 12KHz to 20MHz

2.5V or 3.3V

Q

10MHz to 1.5GHz

Q

OE

XTAL_IN

XTAL_OUT

FSEL1

FSEL0

10MHz to60MHz

Enable

Freq Select

XR81112