The LMX2364 integrates a high performance 2.6 GHz fractional frequency synthesizer with a 850 MHz low power Integer-N frequency synthesizer. Designed for use in a local oscillator subsystem of a radio transceiver, the LMX2364 generates very stable, low noise control signals for UHF and VHF voltage controlled oscillators. It is fabricated using National's high performance BiCMOS process. The RF Synthesizer supports both fractional and integer modes. The N counter contains a selectable, quadruple modulus prescaler and can support fractional denominators from 1 to 128. A flexible, 4 level programmable charge pump supplies output current magnitudes ranging from 1 mA to 16 mA. Only a single word write is required to power up and tune the synthesizer to a new frequency. High performance FastLockTM technology makes the LMX2364 an excellent choice for applications requiring aggressive lock time while maintaining excellent phase noise and spurious performance. The combination of the improved FastLock circuitry, the enhanced fractional compensation engine, and the programmable charge pump architecture gives the designer maximum freedom to optimize the performance of the synthesizer for the target application. Integrated timeout counters greatly simplify the programming aspects of FastLock. These timeout counters reduce the demands on the microcontroller by automatically disengaging FastLock after a perscribed number of reference cycles of the phase detector.