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
  Spurs
• 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
    VCO)
  • 9-mA Typical PLL Mode (External VCO)
• 24-Bit Fractional-N Delta Sigma Modulator