Wideband Frequency Synthesizer with Integrated VCO

Wideband Frequency Synthesizer with Integrated VCO - LMX2581

Recommended alternative parts

  • LMX2541  - The device has SIMILAR FUNCTIONALITY but is not functionally equivalent to the compared device.   RF Synthesizer With Extremely Low Spurs
  • LMX2531  - The device has SIMILAR FUNCTIONALITY but is not functionally equivalent to the compared device.   Very Low Power RF Synthesizer


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.


  • 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

View more

Parametrics Compare all products in RF PLLs and Synthesizers

Output Frequency (Min) (MHz)
Output Frequency (Max) (MHz)
Normalized PLL Phase Noise (dBc/Hz)
VCO Phase Noise (Nom) (dBc/Hz)
1/f Noise (10 kHz offset at 1 GHz carrier) (dBc/Hz)
Current Consumption (mA)
Integrated VCO
LMX2581 LMX2485E LMX2571 LMX2581E LMX2582 LMX2592 TRF3765
50    50    10    50    20    20    300   
3760    3000    1344    3800    5500    9800    4800   
-229    -210    -231    -229    -231    -231    -221   
-121    N/A    -115    -121    -129    -129    -133   
-125    -104    -124    -125    -126    -126    -106   
178    3.3    39    178    250    250    115   
3.15 to 3.45    2.5 to 3.6    3.15 to 5    3.15 to 3.45    3.15 to 3.45    3.15 to 3.45    3.3   
Yes    No    Yes    Yes    Yes    Yes    Yes   
32WQFN    24WQFN      32WQFN    40VQFN    40VQFN    32VQFN   

WEBENCH® Designer LMX2581

Recommend Input Frequency Tunable Output Frequency
Input Frequency Min Output Frequency
 MHz  MHz
Max Output Frequency
Channel Spacing