Abstract
The LMX2350/2352 is part of a family of monolithic integrated fractional N/ Integer N frequency synthesizers designed to be used in a local oscillator subsystem for a radio transceiver. It is fabricated using National’s 0.5μ ABiC V silicon BiCMOS process. The LMX2350/2352 contains dual modulus prescalers along with modulo 15 or 16 fractional compensation circuitry in the RF divider. A 16/17 or 32/33 prescale ratio can be selected for the LMX2350, and the LMX2352 provides 8/9 or 16/17 prescale ratios. The IF circuitry for both the LMX2350 and LMX2352 contains an 8/9 prescaler, and is fully programmable. Using a fractional N phase locked loop technique, the LMX2350 /52 can generate very stable low noise control signals for UHF and VHF voltage controlled oscillators (VCOs).
For the RF PLL, a highly flexible 16 level programmable charge pump supplies output current magnitudes from 100μA to 1.6mA. Two uncommitted CMOS outputs can be used to provide external control signals, or configured to FastLock mode. Serial data is transferred into the LMX2350/2352 via a three wire interface (Data, LE, Clock). Supply voltage can range from 2.7 V to 5.5 V. The LMX2350/ LMX2352 family features very low current consumption; typically LMX2350 (2.5 GHz) 6.5 mA, LMX2352 (1.2 GHz) 4.75mA at 3.0V. The LMX2350/2352 are available in a 24-pin TSSOP and 24-pin CSP surface mount plastic package.
key words：frequency synthesizers 、phase locked loop、programmable
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