1 Features
1• Output Frequency from 50 to 3760 MHz
• Input Clock Frequency up to 900 MHz
• Phase Detector Frequency up to 200 MHz
• Supports Fractional and Integer Modes
• –229 dBc/Hz Normalized PLL Phase Noise
• –120.8 dBc/Hz Normalized PLL 1/f Noise
• –137 dBc/Hz VCO Phase Noise @ 1 MHz offset
for a 2.5 GHz Carrier
• 100 fs RMS Jitter in Integer Mode
• Programmable Fractional Modulator Order
• Programmable Fractional Denominator
• Programmable Output Power up to +12 dBm
• Programmable 32 Level Charge Pump Current
• Programmable Option to Use an External VCO
• Digital Lock Detect
• 3-Wire Serial Interface and Readback
• Single Supply Voltage from 3.15 V to 3.45 V
• Supports Logic Levels down to 1.6 V

2 Applications
• Wireless Infrastructure (UMTS, LTE, WiMax,
Multi-Standard Base Stations)
• Broadband Wireless
• Test and Measurement
• Clock Generation

3 Description
The LMX2581 is a low noise wideband frequency
synthesizer that integrates a delta-sigma fractional N PLL, multiple core VCO, programmable output
divider, and two differential output buffers. The VCO
frequency range is from 1880 to 3760 MHz and can
be sent directly to the output buffers or divided down by even values from 2 to 38. Each buffer is capable
of output power from -3 to +12 dBm at 2700 MHz.
Integrated low noise LDOs are used for superior
noise immunity and consistent performance.
This synthesizer is a highly programmable device and
it enables the user to optimize its performance. In
fractional mode, the denominator and the modulator order are programmable and can be configured with
dithering as well. The user also has the ability to
directly specify a VCO core or entirely bypass the
internal VCO. Finally, many convenient features are
included such as power down, Fastlock, auto mute,
and lock detection. All registers can be programmed
through a simple 3 wire interface and a read back
feature is also available.
The LMX2581 operates on a single 3.3 V supply and
comes in a 32 pin 5.0 mm × 5.0 mm WQFN package.