OBSOLETE
LMX2471
www.ti.com
SNAS213A –MAY 2004–REVISED MAY 2004
LMX2471 3.6 GHz Delta-Sigma Fractional-N PLL with 1.7 GHz Integer-N PLL
Check for Samples: LMX2471
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FEATURES
– IF PLL: 8/9 or 16/17
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Crystal Reference Frequency up to 110 MHz
On-chip crystal reference frequency doubler.
Phase Comparison Frequency up to 50 MHz
Hardware and software power-down control
Ultra low consumption: ICC = 5.6 mA (typical)
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Low in-band phase noise and low fractional
spurs
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12 bit or 22 bit selectable fractional modulus
Up to 4th order programmable delta-sigma
modulator
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Enhanced Anti-Cycle Slip Fastlock Circuitry
APPLICATIONS
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Fastlock
Cycle slip reduction
Integrated timeout counters
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Cellular Phones and Base Stations
Applications requiring fine frequency
resolution
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Digital lock detect output
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Satellite and Cable TV Tuners
WLAN Standards
Prescalers allow wide range of N values
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RF PLL: 16/17/20/21
DESCRIPTION
The LMX2471 is a low power, high performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL.
The device is fabricated using National Semiconductor’s advanced BiCMOS process.
With delta-sigma architecture, fractional spur compensation is achieved with noise shaping capability of the delta-
sigma modulator and the inherent low pass filtering of the PLL loop filter. Fractional spurs at lower frequencies
are pushed to higher frequencies outside the loop bandwidth. Unlike analog compensation, the digital feedback
techniques used in the LMX2471 are highly resistant to changes in temperature and variations in wafer
processing. With delta-sigma architecture, the ability to push close in spur and phase noise energy to higher
frequencies is a direct function of the modulator order. The higher the order, the more this energy can be spread
to higher frequencies. The LMX2471 has a programmable modulator up to order four, which allows the designer
to select the optimum modulator order to fit the phase noise, spur, and lock time requirements of the system.
Programming is fast and simple. Serial data is transferred into the LMX2471 via a three line MICROWIRE
interface (Data, Clock, Load Enable). Nominal supply voltage is 2.5 V. The LMX2471 features a typical current
consumption of 5.6 mA at 2.5 V. The LMX2471 is available in a 24 lead 3.5 X 4.5 X 0.6 mm package.
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PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004, Texas Instruments Incorporated