LMX2471 Datasheet, PDF (1/36 Pages) National Semiconductor (TI) – 3.6 GHz Delta-Sigma Fractional-N PLL with 1.7 GHz Integer-N PLL

November 2003
LMX2471
3.6 GHz Delta-Sigma Fractional-N PLL with 1.7 GHz
Integer-N PLL
General 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 BiC-
MOS 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 ana-
log compensation, the digital feedback techniques used in
the LMX2471 are highly resistant to changes in temperature
and variations in wafer processing. With delta-sigma archi-
tecture, the ability to push close in spur and phase noise
energy to higher frequencies is a direct function of the modu-
lator order. The higher the order, the more this energy can be
spread to higher frequencies. The LMX2471 has a program-
mable 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.
Features
n Low in-band phase noise and low fractional spurs
n 12 bit or 22 bit selectable fractional modulus
n Up to 4th order programmable delta-sigma modulator
n Enhanced Anti-Cycle Slip Fastlock Circuitry
Fastlock
Cycle slip reduction
Integrated timeout counters
n Digital lock detect output
n Prescalers allow wide range of N values
RF PLL: 16/17/20/21
IF PLL: 8/9 or 16/17
n Crystal Reference Frequency up to 110 MHz
n On-chip crystal reference frequency doubler.
n Phase Comparison Frequency up to 50 MHz
n Hardware and software power-down control
n Ultra low consumption: I_CC = 5.6 mA (typical)
Applications
n Cellular Phones and Base Stations
n Applications requiring fine frequency resolution
n Satellite and Cable TV Tuners
n WLAN Standards
Functional Block Diagram
© 2003 National Semiconductor Corporation DS200721
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