LMX2491 Low-Noise Fractional N PLL Texas Instruments LMX2491 Low-Noise Fractional-N PLL is a 6.4GHz wideband delta-sigma fractional-N PLL with ramp and chirp generation. This device consists of a phase-frequency detector, programmable charge pump, and high-frequency input for the external VCO. The LMX2491 supports a broad and flexible class of ramping capabilities, including FSK, PSK, and configurable piecewise linear FM modulation profiles of up to 8 segments. The device supports fine PLL resolution and fast ramp with a phase detector rate of up to 200MHz. The LMX2491 allows any of its registers to be read back. The LMX2491 can operate with a single 3.3V supply. Moreover, supporting up to a 5.25V charge pump can eliminate the need for an external amplifier, leading to a simpler solution with improved phase noise performance.