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LMX2470SLEX
2.6 GHz Delta-Sigma Fractional-N PLL with 800 MHz Integer-N PLL
LMX2470
2.6 GHz Delta-Sigma Fractional-N PLL with 800 MHz
Integer-N PLL
General DescriptionThe LMX2470isa low power, high performance delta-sigma
fractional-N PLL withan auxiliary integer-N PLL. The device fabricated using National Semiconductor’s advanced BiC-
MOS process.
With delta-sigma architecture, fractional spur compensation achieved with noise shaping capabilityof the delta-sigma
modulator andthe inherent low pass filteringofthe PLL loop
filter. Fractional spursat lower frequencies are pushedto
higher frequencies outsidethe loop bandwidth. Unlike ana-
log compensation, the digital feedback techniques usedin
the LMX2470are highly resistantto changesin temperature
and variationsin wafer processing. With delta-sigma archi-
tecture, the abilityto push closein spur and phase noise
energyto higher frequenciesisa direct functionofthe modu-
lator order. The higherthe order,the more this energy canbe
spreadto higher frequencies. The LMX2470 hasa program-
mable modulatorupto order four, which allowsthe designer selectthe optimum modulator ordertofitthe phase noise,
spur, and lock time requirementsofthe system.
Programmingis fast and simple. Serial datais transferred
into the LMX2470 viaa three line MICROWIRE interface
(Data, Clock, Load Enable). Nominal supply voltageis2.5V.
The LMX2470 featuresa typical current consumptionof 4.1at2.5V. The LMX2470is availableina24 lead3.5X4.5 0.6 mm package.
Features Low in-band phase noise and low fractional spurs12bitor22bit selectable fractional modulus Upto4th order programmable delta-sigma modulator Enhanced Anti-Cycle Slip Fastlock Circuitry
Fastlock
Cycle slip reduction
Integrated timeout counters Digital lock detect output Prescalers allow wide rangeofN values PLL: 16/17/20/21 PLL:8/9or 16/17 Crystal Reference Frequencyupto 110 MHz On-chip crystal reference frequency doubler. Phase Comparison Frequencyupto30 MHz Hardware and software power-down control Ultra low consumption: ICC= 4.1 mA (typical)
Applications Cellular Phones and Base Stations
CDMA, WCDMA, GSM/GPRS, TDMA, EDGE, PDC Applications requiring fine frequency resolution Satellite and CableTV Tuners WLAN Standards
Functional Block DiagramApril 2003
LMX2470
GHz
Delta-Sigma
Fractional-N
PLL
with
MHz
Integer-N
PLL
