描述 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.特性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