LMX2541 - Ultra-Low Noise PLLatinum Frequency Synthesizer with Integrated VCO

The LMX2541 is an ultra low-noise frequency synthesizer which integrates a high performance delta-sigma fractional N PLL, a VCO with fully integrated tank circuit, and an optional frequency divider. The PLL offers an unprecedented normalized noise floor of -225 dBc/Hz and can be operated with up to 104 MHz of phase-detector rate (comparison frequency) in both integer and fractional modes. The PLL can also be configured to work with an external VCO.

The LMX2541 integrates several low-noise, high precision LDOs and output driver matching network to provide higher supply noise immunity and more consistent performance, while reducing the number of external components. When combined with a high quality reference oscillator, the LMX2541 generates a very stable, ultra low-noise signal.

The LMX2541 is offered in a family of 6 devices with varying VCO frequency range from 1990 MHz up to 4 GHz. Using a flexible divider, the LMX2541 can generate frequencies as low as 31.6 MHz.

The LMX2541 is a monolithic integrated circuit, fabricated in a proprietary BiCMOS process. Device programming is facilitated using a three-wire MICROWIRE interface that can operate down to 1.6 volts. Supply voltage ranges from 3.15 V to 3.45 V. The LMX2541 is available in a 36-pin 6-mm × 6-mm × 0.8-mm WQFN Package.

• Multiple Frequency Options Available
  (See Device Comparison Table)
• Frequencies from 31.6 MHz to 4000 MHz
• Very Low RMS Noise and Spurs
• –225 dBc/Hz Normalized PLL Phase Noise
• Integrated RMS Noise (100 Hz – 20 MHz)
  • 2 mRad (100 Hz – 20 MHz) at 2.1 GHz
  • 3.5 mRad (100 Hz - 20 MHz) at 3.5 GHz
• Ultra Low-Noise Integrated VCO
• External VCO Option (Internal VCO Bypassed)
• VCO Frequency Divider 1 to 63 (all values)
• Programmable Output Power
• Up to 104-MHz Phase Detector Frequency
• Integrated Low-Noise LDOs
• Programmable Charge Pump Output
• Partially Integrated Loop Filter
• Digital Frequency Shift Keying (FSK) Modulation Pin
• Integrated Reference Crystal Oscillator Circuit
• Hardware and Software Power Down
• FastLock Mode and VCO-Based Cycle Slip Reduction
• Analog and Digital Lock Detect
• 1.6-V Logic Compatibility