LMX2571 Low Power Synthesizer with FSK Modulation - LMX2571


LMX2571 Low Power Synthesizer with FSK Modulation



The LMX2571 is a low-power, high-performance, wideband PLLatinum RF synthesizer that integrates a delta-sigma fractional N PLL, multiple core voltage-controlled oscillator (VCO), programmable output dividers and two output buffers. The VCO cores work up to 5.376 GHz resulting in continuous output frequency range of 10 MHz to 1344 MHz.

This synthesizer can also be used with an external VCO. To that end, a dedicated 5-V charge pump and an output divider are available for this configuration.

A unique programmable multiplier is also incorporated to help improve spurs, allowing the system to use every channel even if it falls on an integer boundary.

The output has an integrated SPDT switch that can be used as a transmit/receive switch in FDD radio application. Both outputs can also be turned on to provide 2 outputs at the same time.

The LMX2571 supports direct digital FSK modulation through programming or pins. Discrete level FSK, pulse shaping FSK, and analog FM modulation are supported.

A new FastLock technique can be used allowing the user to step from one frequency to the next in less than 1.5 ms even when an external VCO is used with a narrow band loop filter.


  • Any Frequency from 10 MHz to 1344 MHz
  • Low Phase Noise and Spurs
    • –123 dBc/Hz at 12.5 kHz Offset at 480 MHz
    • –145 dBc/Hz at 1 MHz Offset at 480 MHz
    • Normalized PLL Noise Floor of –231 dBc/Hz
    • Spurious Better Than –75 dBc/Hz
  • New FastLock to Reduce Lock Time
  • A Novel Technique to Remove Integer Boundary
  • Integrated 5-V Charge Pump and Output Divider
    for External VCO Operation
  • 2-, 4- and 8-Level or Arbitrary Level Direct Digital
    FSK Modulation
  • One TX/RX Output or Two Fanout Outputs
  • Crystal, XO or Differential Reference Clock Input
  • Low Current Consumption
    • 39-mA Typical Synthesizer Mode (Internal
    • 9-mA Typical PLL Mode (External VCO)
  • 24-Bit Fractional-N Delta Sigma Modulator

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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
LMX2571 LMX2485E LMX2581 LMX2581E LMX2582 LMX2592 LMX2594
10    50    50    50    20    20    10   
1344    3000    3760    3800    5500    9800    15000   
-231    -210    -229    -229    -231    -231    -236   
-115      -121    -121    -129    -129     
-124    -104    -125    -125    -126    -126    -129   
39    3.3    178    178    250    250    340 mA   
3.15 to 5    2.5 to 3.6    3.15 to 3.45    3.15 to 3.45    3.15 to 3.45    3.15 to 3.45    3.3   
Yes    No    Yes    Yes    Yes    Yes    Yes   
  24WQFN    32WQFN    32WQFN    40VQFN    40VQFN    40VQFN   

WEBENCH® Designer LMX2571

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