LMX2487E Datasheet, PDF (1/38 Pages) Texas Instruments – Low-Power Dual PLLatinum Frequency Synthesizers

May 2007
LMX2487E
7.5 GHz High Performance Delta-Sigma Low Power Dual
PLLatinum™ Frequency Synthesizers with 3.0 GHz Integer
PLL
General Description
■ ^{WLAN Standards}
The LMX2487E is a low power, high performance delta-sigma
fractional-N PLL with an auxiliary integer-N PLL. It is fabricat-
ed using National Semiconductor’s 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 mod-
ulator order. Unlike analog compensation, the digital feed-
back technique used in the LMX2487E is highly resistant to
changes in temperature and variations in wafer processing.
The LMX2487E delta-sigma modulator is programmable up
to fourth order, which allows the designer to select the opti-
mum modulator order to fit the phase noise, spur, and lock
time requirements of the system.
Serial data for programming the LMX2487E is transferred via
a three line high speed (20 MHz) MICROWIRE interface. The
LMX2487E 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 LMX2487E is available in a 24 lead
4.0 X 4.0 X 0.8 mm LLP package.
Applications
■ ^{Cellular phones and base stations}
■ ^{Direct digital modulation applications}
■ ^{Satellite and cable TV tuners}
Features
Quadruple Modulus Prescalers for Lower Divide Ratios
■ ^{RF PLL: 16/17/20/21 or 32/33/36/37}
■ ^{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 Times and Programming
■ ^{Fastlock / Cycle slip reduction}
■ ^{Integrated time-out counter}
■ ^{Single word write to change frequencies with Fastlock}
Wide Operating Range
■ ^{LMX2487E RF PLL: 3.0 GHz to 7.5 GHz}
Useful Features
■ ^{Digital lock detect output}
■ ^{Hardware and software power-down control}
■ ^{On-chip crystal reference frequency doubler.}
■ ^{RF phase comparison frequency up to 50 MHz}
■ ^{2.5 to 3.6 volt operation with I}_CC ^{= 8.5 mA at 3.0 V}
Functional Block Diagram
PLLatinum™ is a trademark of National Semiconductor Corporation.
© 2007 National Semiconductor Corporation 300139
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