The LMX233xU devices are high performance frequency synthesizers with integrated dual modulus prescalers. The LMX233xU devices are designed for use as RF and IF local oscillators for dual conversion radio transceivers. A 32/33 or a 64/65 prescale ratio can be selected for the 2.5 GHz LMX2330U RF synthesizer. A 64/65 or a 128/129 prescale ratio can be selected for both the LMX2331U and LMX2332U RF synthesizers. The IF circuitry contains an 8/9 or a 16/17 prescaler. Using a proprietary digital phase locked loop technique, the LMX233xU devices generate very stable, low noise control signals for RF and IF voltage controlled oscillators. Both the RF and IF synthesizers include a two-level programmable charge pump. The RF synthesizer has dedicated Fastlock circuitry.