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.