LMX2364

The LMX2364 integrates a high performance 2.6 GHz frac-tional frequency synthesizer with a 850 MHz low powerInteger-N frequency synthesizer. Designed for use in a localoscillator subsystem of a radio transceiver, the LMX2364generates very stable, low noise control signals for UHF andVHF voltage controlled oscillators. It is fabricated using Na-tional's high performance BiCMOS process.

The RF Synthesizer supports both fractional and integermodes. The N counter contains a selectable, quadruplemodulus prescaler and can support fractional denominatorsfrom 1 to 128. A flexible, 4 level programmable charge pumpsupplies output current magnitudes ranging from 1 mA to 16mA. Only a singleword write is required to power up andtune the synthesizer to a new frequency.

High performance FastLock™ technology makes theLMX2364 an excellent choice for applications requiring ag-gressive lock time while maintaining excellent phase noiseand spurious performance. The combination of the improvedFastLock circuitry, the enhanced fractional compensationengine, and theprogrammable charge pump architecturegives the designer maximum freedom to optimize the perfor-mance of the synthesizer for the target application. Inte-grated timeout counters greatly simplify the programmingaspects of FastLock. These timeout counters reduce thedemands on the microcontroller by automatically disengag-ing FastLock after a perscribed number of reference cyclesof the phase detector.

The IF synthesizer includes a fixed 8/9 dual modulus pres-caler, a two level programmable charge pump, and dedi-cated FastLock circuitry with an integrated timeout counter.The LMX2364 offers many performance enhancements overthe LMX2354. Improvements in the fractional compensationmake the spurs on the LMX2364 approximately 6 dB betterin a typical application. The higher and more flexible frac-tional modulus combined with the higher charge pump cur-rents result in phase noise improvements on the order of 10dB. The cycle slip reduction circuitry of the LMX2364 is botheasy to use and effective in reducing cycle slipping andallows one to use very high phase detector frequencieswithout degrading lock times.

Serial data is transferred to the device via a three-wireinterface (DATA, LE, CLK). The low voltage logic interfaceallows direct connection to 1.8 Volt and 3.0 Volt devices.Supply voltages from 2.7V to 5.5V are supported. Indepen-dent charge pump supplies for each synthesizer allows thedesigner to optimize the bias level for the selected VCO. TheLMX2364 consumes 5.0 mA (typical) of current in integermode and 7.2 mA (typical) in fractional mode. The LMX2364is available in a 24 Pin Ultra Thin CSP package and 24 PinTSSOP Package.