1 Features
1• Quadruple Modulus Prescaler for Lower Divides
– RF PLL: 8/9/12/13 or 16/17/20/21
– IF PLL: 8/9 or 16/17
• Advanced Delta-Sigma Fractional Compensation
– 12-Bit or 22-Bit Selectable Fractional Modulus
– Up to 4th Order Programmable Delta-Sigma
Modulator
• Features for Improved Lock Time
– Fastlock / Cycle Slip Reduction With Integrated
Time-Out Counter Which Requires Only a
Single-Word Write
• Wide Operating Range
– LMX2485 RF PLL: 500 MHz to 3.0 GHz
– LMX2485E RF PLL: 50 MHz to 3.0 GHz
• Useful Features
– Digital Lock Detect Output
– Hardware and Software Power-Down Control
– On-Chip Input Frequency Doubler.
– RF Phase Detector Frequency up to 50 MHz
– 2.5 to 3.6 V Operation With I CC = 5.0 mA

2 Applications
• Cellular Phones and Base Stations
• Direct Digital Modulation Applications
• Satellite and Cable TV Tuners
• WLAN Standards

3 Description
The LMX2485 device is a low power, high
performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL. The device is fabricated
using Texas Instruments' advanced process.
With delta-sigma architecture, fractional spurs at
lower offset frequencies are pushed to higher
frequencies outside the loop bandwidth. The ability to
push close in spur and phase noise energy to higher
frequencies is a direct function of the modulator
order. Unlike analog compensation, the digital
feedback technique used in the LMX2485 is highly
resistant to changes in temperature and variations in
wafer processing. The LMX2485 delta-sigma
modulator is programmable up to fourth order, which allows the designer to select the optimum modulator
order to fit the phase noise, spur, and lock time
requirements of the system.
Serial data for programming the LMX2485 is
transferred through a three-line, high-speed (20-MHz)
MICROWIRE interface. The LMX2485 offers fine frequency resolution, low spurs, fast programming
speed, and a single-word write to change the
frequency. This makes it ideal for direct digital
modulation applications, where the N-counter is
directly modulated with information. The LMX2485 is
available in a 24-lead 4.0 × 4.0 × 0.8 mm WQFN package.