The LMX2470 is a low power, high performance delta-sigma fractional-N PLL with an
auxiliary integer-N PLL. The device is fabricated using TI’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 LMX2470 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 LMX2470 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 LMX2470 via a three
line MICROWIRE interface (Data, Clock, Load Enable). Nominal supply voltage is 2.5 V. The LMX2470
features a typical current consumption of 4.1 mA at 2.5 V. The LMX2470 is available in a 24 lead
3.5 X 4.5 X 0.6 mm package.
