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.