Si4133 is a monolithic integrated circuit that performs both IF and dual-band RF synthesis for wireless communications applications. The Si4133 includes three VCOs, loop filters, reference and VCO dividers, and phase detectors. Divider and power-down settings are programmable through a three-wire serial interface. Features include dual-band RF synthesizers, IF synthesizer, integrated VCOs, loop filters, varactors, and resonators, minimal external components required, low phase noise, programmable power down modes, 1µA standby current, 18mA typical supply current, 2.7V to 3.6V operation, and 24-pin TSSOP and 28-lead MLP packages.