LMX2491 6.4GHz Low Noise Fractional N PLL With Ramp/Chirp Generation | TI.com

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6.4GHz Low Noise Fractional N PLL With Ramp/Chirp Generation



The LMX2491 device is a low-noise, 6.4-GHz wideband delta-sigma fractional N PLL with ramp and chirp generation. It consists of a phase frequency detector, programmable charge pump, and high frequency input for the external VCO. The LMX2491 supports a broad and flexible class of ramping capabilities, including FSK, PSK, and configurable piecewise linear FM modulation profiles of up to 8 segments. It supports fine PLL resolution and fast ramp with up to a 200-MHz phase detector rate. The LMX2491 allows any of its registers to be read back. The LMX2491 can operate with a single 3.3-V supply. Moreover, supporting up to 5.25-V charge pump can eliminate the need of external amplifier, leading to a simpler solution with improved phase noise performance.


  • –227-dBc/Hz Normalized PLL Noise
  • 500-MHz to 6.4-GHz Wideband PLL
  • 3.15-V to 5.25-V Charge Pump PLL Supply
  • Versatile Ramp / Chirp Generation
  • 200-MHz Maximum Phase Detector Frequency
  • FSK / PSK Modulation Pin
  • Digital Lock Detect
  • Single 3.3-V Supply Capability


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Part number Order Output frequency (Min) (MHz) Output frequency (Max) (MHz) Normalized PLL phase noise (dBc/Hz) 1/f noise (10-kHz offset at 1-GHz carrier) (dBc/Hz) Current consumption (mA) VCC (V) Integrated VCO
LMX2491 Order now 500     6400     -227     -120     60     3.15 to 3.45     No    
LMX2485E Order now 50     3000     -210     -104     3.3     2.5 to 3.6     No